[PATCH v2 01/11] stm class: Introduce an abstraction for System Trace Module devices

[Alexander Shishkin]

A System Trace Module (STM) is a device exporting data in System Trace
Protocol (STP) format as defined by MIPI STP standards. Examples of such
devices are Intel Trace Hub and Coresight STM.

This abstraction provides a unified interface for software trace sources
to send their data over an STM device to a debug host. In order to do
that, such a trace source needs to be assigned a pair of master/channel
identifiers that all the data from this source will be tagged with. The
STP decoder on the debug host side will use these master/channel tags to
distinguish different trace streams from one another inside one STP
stream.

This abstraction provides a configfs-based policy management mechanism
for dynamic allocation of these master/channel pairs based on trace
source-supplied string identifier. It has the flexibility of being
defined at runtime and at the same time (provided that the policy
definition is aligned with the decoding end) consistency.

For userspace trace sources, this abstraction provides write()-based and
mmap()-based (if the underlying stm device allows this) output mechanism.

For kernel-side trace sources, we provide "stm_source" device class that
can be connected to an stm device at run time.

Cc: linux-api@xxxxxxxxxxxxxxx
Cc: Pratik Patel <pratikp@xxxxxxxxxxxxxx>
Cc: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
Signed-off-by: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
---
 Documentation/ABI/testing/configfs-stp-policy    |  44 ++
 Documentation/ABI/testing/sysfs-class-stm        |  14 +
 Documentation/ABI/testing/sysfs-class-stm_source |  11 +
 Documentation/trace/stm.txt                      |  77 ++
 drivers/Kconfig                                  |   2 +
 drivers/Makefile                                 |   1 +
 drivers/hwtracing/stm/Kconfig                    |   8 +
 drivers/hwtracing/stm/Makefile                   |   3 +
 drivers/hwtracing/stm/core.c                     | 897 +++++++++++++++++++++++
 drivers/hwtracing/stm/policy.c                   | 467 ++++++++++++
 drivers/hwtracing/stm/stm.h                      |  79 ++
 include/linux/stm.h                              | 102 +++
 include/uapi/linux/stm.h                         |  47 ++
 13 files changed, 1752 insertions(+)
 create mode 100644 Documentation/ABI/testing/configfs-stp-policy
 create mode 100644 Documentation/ABI/testing/sysfs-class-stm
 create mode 100644 Documentation/ABI/testing/sysfs-class-stm_source
 create mode 100644 Documentation/trace/stm.txt
 create mode 100644 drivers/hwtracing/stm/Kconfig
 create mode 100644 drivers/hwtracing/stm/Makefile
 create mode 100644 drivers/hwtracing/stm/core.c
 create mode 100644 drivers/hwtracing/stm/policy.c
 create mode 100644 drivers/hwtracing/stm/stm.h
 create mode 100644 include/linux/stm.h
 create mode 100644 include/uapi/linux/stm.h

diff --git a/Documentation/ABI/testing/configfs-stp-policy b/Documentation/ABI/testing/configfs-stp-policy
new file mode 100644
index 0000000000..1c7ab3dbcd
--- /dev/null
+++ b/Documentation/ABI/testing/configfs-stp-policy
@@ -0,0 +1,44 @@
+What:		/config/stp-policy
+Date:		Jan 2015
+KernelVersion:	3.20
+Description:
+		This group contains policies mandating Master/Channel allocation
+		for software sources wishing to send trace data over an STM
+		device.
+
+What:		/config/stp-policy/<policy>
+Date:		Jan 2015
+KernelVersion:	3.20
+Description:
+		Root of a policy. This name is an arbitrary string.
+
+What:		/config/stp-policy/<policy>/device
+Date:		Jan 2015
+KernelVersion:	3.20
+Description:
+		STM device to which this policy applies. Write a valid stm class
+		device name here to assign this policy to that device.
+
+What:		/config/stp-policy/<policy>/<node>
+Date:		Jan 2015
+KernelVersion:	3.20
+Description:
+		Policy node is a string identifier that software clients will
+		use to request a master/channel to be allocated and assigned to
+		them.
+
+What:		/config/stp-policy/<policy>/<node>/masters
+Date:		Jan 2015
+KernelVersion:	3.20
+Description:
+		Range of masters from which to allocate for users of this node.
+		Write two numbers: the first master and the last master number.
+
+What:		/config/stp-policy/<policy>/<node>/channels
+Date:		Jan 2015
+KernelVersion:	3.20
+Description:
+		Range of channels from which to allocate for users of this node.
+		Write two numbers: the first channel and the last channel
+		number.
+
diff --git a/Documentation/ABI/testing/sysfs-class-stm b/Documentation/ABI/testing/sysfs-class-stm
new file mode 100644
index 0000000000..186f8e66e1
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-stm
@@ -0,0 +1,14 @@
+What:		/sys/class/stm/<stm>/masters
+Date:		Jan 2015
+KernelVersion:	3.20
+Contact:	Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
+Description:
+		Shows first and last available to software master numbers on
+		this STM device.
+
+What:		/sys/class/stm/<stm>/channels
+Date:		Jan 2015
+KernelVersion:	3.20
+Contact:	Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
+Description:
+		Shows the number of channels per master on this STM device.
diff --git a/Documentation/ABI/testing/sysfs-class-stm_source b/Documentation/ABI/testing/sysfs-class-stm_source
new file mode 100644
index 0000000000..735b0d657f
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-stm_source
@@ -0,0 +1,11 @@
+What:		/sys/class/stm_source/<stm_source>/stm_source_link
+Date:		Jan 2015
+KernelVersion:	3.20
+Contact:	Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
+Description:
+		stm_source device linkage to stm device, where its tracing data
+		is directed. Reads return an existing connection or "<none>" if
+		this stm_source is not connected to any stm device yet.
+		Write an existing (registered) stm device's name here to
+		connect that device. If a device is already connected to this
+		stm_source, it will first be disconnected.
diff --git a/Documentation/trace/stm.txt b/Documentation/trace/stm.txt
new file mode 100644
index 0000000000..0ba5c9115c
--- /dev/null
+++ b/Documentation/trace/stm.txt
@@ -0,0 +1,77 @@
+System Trace Module
+===================
+
+System Trace Module (STM) is a device described in MIPI STP specs as
+STP trace stream generator. STP (System Trace Protocol) is a trace
+protocol multiplexing data from multiple trace sources, each one of
+which is assigned a unique pair of master and channel. While some of
+these masters and channels are statically allocated to certain
+hardware trace sources, others are available to software. Software
+trace sources are usually free to pick for themselves any
+master/channel combination from this pool.
+
+On the receiving end of this STP stream (the decoder side), trace
+sources can only be identified by master/channel combination, so in
+order for the decoder to be able to make sense of the trace that
+involves multiple trace sources, it needs to be able to map those
+master/channel pairs to the trace sources that it understands.
+
+For instance, it is helpful to know that syslog messages come on
+master 7 channel 15, while arbitrary user applications can use masters
+48 to 63 and channels 0 to 127.
+
+To solve this mapping problem, stm class provides a policy management
+mechanism via configfs, that allows defining rules that map string
+identifiers to ranges of masters and channels. If these rules (policy)
+are consistent with what decoder expects, it will be able to properly
+process the trace data.
+
+This policy is a tree structure containing rules (policy_node) that
+have a name (string identifier) and a range of masters and channels
+associated with it, located in "stp-policy" subsystem directory in
+configfs. From the examle above, a rule may look like this:
+
+$ ls /config/stp-policy/my-policy/user
+channels masters
+$ cat /config/stp-policy/my-policy/user/masters
+48 63
+$ cat /config/stp-policy/my-policy/user/channels
+0 127
+
+which means that the master allocation pool for this rule consists of
+masters 48 through 63 and channel allocation pool has channels 0
+through 127 in it. Now, any producer (trace source) identifying itself
+with "user" identification string will be allocated a master and
+channel from within these ranges.
+
+These rules can be nested, for example, one can define a rule "dummy"
+under "user" directory from the example above and this new rule will
+be used for trace sources with the id string of "user/dummy".
+
+Trace sources have to open the stm class device's node and write their
+trace data into its file descriptor. In order to identify themselves
+to the policy, they need to do a STP_POLICY_ID_SET ioctl on this file
+descriptor providing their id string. Otherwise, they will be
+automatically allocated a master/channel pair upon first write to this
+file descriptor according to the "default" rule of the policy, if such
+exists.
+
+Some STM devices may allow direct mapping of the channel mmio regions
+to userspace for zero-copy writing. One mappable page (in terms of
+mmu) will usually contain multiple channels' mmios, so the user will
+need to allocate that many channels to themselves (via the
+aforementioned ioctl() call) to be able to do this. That is, if your
+stm device's channel mmio region is 64 bytes and hardware page size is
+4096 bytes, after a successful STP_POLICY_ID_SET ioctl() call with
+width==64, you should be able to mmap() one page on this file
+descriptor and obtain direct access to an mmio region for 64 channels.
+
+For kernel-based trace sources, there is "stm_source" device
+class. Devices of this class can be connected and disconnected to/from
+stm devices at runtime via a sysfs attribute.
+
+Examples of STM devices are Intel Trace Hub [1] and Coresight STM
+[2].
+
+[1] https://software.intel.com/sites/default/files/managed/d3/3c/intel-th-developer-manual.pdf
+[2] http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0444b/index.html
diff --git a/drivers/Kconfig b/drivers/Kconfig
index c0cc96bab9..9850ab81cc 100644
--- a/drivers/Kconfig
+++ b/drivers/Kconfig
@@ -182,4 +182,6 @@ source "drivers/thunderbolt/Kconfig"
 
 source "drivers/android/Kconfig"
 
+source "drivers/hwtracing/stm/Kconfig"
+
 endmenu
diff --git a/drivers/Makefile b/drivers/Makefile
index 527a6da8d5..87d7c74e39 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -165,3 +165,4 @@ obj-$(CONFIG_RAS)		+= ras/
 obj-$(CONFIG_THUNDERBOLT)	+= thunderbolt/
 obj-$(CONFIG_CORESIGHT)		+= coresight/
 obj-$(CONFIG_ANDROID)		+= android/
+obj-$(CONFIG_STM)		+= hwtracing/stm/
diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
new file mode 100644
index 0000000000..90ed327461
--- /dev/null
+++ b/drivers/hwtracing/stm/Kconfig
@@ -0,0 +1,8 @@
+config STM
+	tristate "System Trace Module devices"
+	help
+	  A System Trace Module (STM) is a device exporting data in System
+	  Trace Protocol (STP) format as defined by MIPI STP standards.
+	  Examples of such devices are Intel Trace Hub and Coresight STM.
+
+	  Say Y here to enable System Trace Module device support.
diff --git a/drivers/hwtracing/stm/Makefile b/drivers/hwtracing/stm/Makefile
new file mode 100644
index 0000000000..adec701649
--- /dev/null
+++ b/drivers/hwtracing/stm/Makefile
@@ -0,0 +1,3 @@
+obj-$(CONFIG_STM)	+= stm_core.o
+
+stm_core-y		:= core.o policy.o
diff --git a/drivers/hwtracing/stm/core.c b/drivers/hwtracing/stm/core.c
new file mode 100644
index 0000000000..9e82634590
--- /dev/null
+++ b/drivers/hwtracing/stm/core.c
@@ -0,0 +1,897 @@
+/*
+ * System Trace Module (STM) infrastructure
+ * Copyright (c) 2014, Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * STM class implements generic infrastructure for  System Trace Module devices
+ * as defined in MIPI STPv2 specification.
+ */
+
+#include <linux/uaccess.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/compat.h>
+#include <linux/kdev_t.h>
+#include <linux/srcu.h>
+#include <linux/slab.h>
+#include <linux/stm.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include "stm.h"
+
+#include <uapi/linux/stm.h>
+
+static unsigned int stm_core_up;
+
+/*
+ * The SRCU here makes sure that STM device doesn't disappear from under a
+ * stm_source_write() caller, which may want to have as little overhead as
+ * possible.
+ */
+static struct srcu_struct stm_source_srcu;
+
+static ssize_t masters_show(struct device *dev,
+			    struct device_attribute *attr,
+			    char *buf)
+{
+	struct stm_device *stm = dev_get_drvdata(dev);
+	int ret;
+
+	ret = sprintf(buf, "%u %u\n", stm->data->sw_start, stm->data->sw_end);
+
+	return ret;
+}
+
+static DEVICE_ATTR_RO(masters);
+
+static ssize_t channels_show(struct device *dev,
+			     struct device_attribute *attr,
+			     char *buf)
+{
+	struct stm_device *stm = dev_get_drvdata(dev);
+	int ret;
+
+	ret = sprintf(buf, "%u\n", stm->data->sw_nchannels);
+
+	return ret;
+}
+
+static DEVICE_ATTR_RO(channels);
+
+static struct attribute *stm_attrs[] = {
+	&dev_attr_masters.attr,
+	&dev_attr_channels.attr,
+	NULL,
+};
+
+static const struct attribute_group stm_group = {
+	.attrs	= stm_attrs,
+};
+
+static const struct attribute_group *stm_groups[] = {
+	&stm_group,
+	NULL,
+};
+
+static struct class stm_class = {
+	.name		= "stm",
+	.dev_groups	= stm_groups,
+};
+
+static int stm_dev_match(struct device *dev, const void *data)
+{
+	const char *name = data;
+
+	return sysfs_streq(name, dev_name(dev));
+}
+
+/**
+ * stm_find_device() - find stm device by name
+ * @buf:	character buffer containing the name
+ * @len:	length of the name in @buf
+ *
+ * This is called from attributes' store methods, so it will
+ * also trim the trailing newline if necessary.
+ *
+ * Return:	device pointer or null if lookup failed.
+ */
+struct device *stm_find_device(const char *buf, size_t len)
+{
+	if (!stm_core_up)
+		return NULL;
+
+	return class_find_device(&stm_class, NULL, buf, stm_dev_match);
+}
+
+/*
+ * Internally we only care about software-writable masters here, that is the
+ * ones in the range [stm_data->sw_start..stm_data..sw_end], however we need
+ * original master numbers to be visible externally, since they are the ones
+ * that will appear in the STP stream. Thus, the internal bookkeeping uses
+ * $master - stm_data->sw_start to reference master descriptors and such.
+ */
+
+#define __stm_master(_s, _m)				\
+	((_s)->masters[(_m) - (_s)->data->sw_start])
+
+static inline struct stp_master *
+stm_master(struct stm_device *stm, unsigned int idx)
+{
+	if (idx < stm->data->sw_start || idx > stm->data->sw_end)
+		return NULL;
+
+	return __stm_master(stm, idx);
+}
+
+static int stp_master_alloc(struct stm_device *stm, unsigned int idx)
+{
+	struct stp_master *master;
+	size_t size;
+
+	size = ALIGN(stm->data->sw_nchannels, 8) / 8;
+	size += sizeof(struct stp_master);
+	master = kzalloc(size, GFP_ATOMIC);
+	if (!master)
+		return -ENOMEM;
+
+	master->nr_free = stm->data->sw_nchannels;
+	__stm_master(stm, idx) = master;
+
+	return 0;
+}
+
+static void stp_master_free(struct stm_device *stm, unsigned int idx)
+{
+	struct stp_master *master = stm_master(stm, idx);
+
+	if (!master)
+		return;
+
+	__stm_master(stm, idx) = NULL;
+	kfree(master);
+}
+
+static void stm_output_claim(struct stm_device *stm, struct stm_output *output)
+{
+	struct stp_master *master = stm_master(stm, output->master);
+
+	if (WARN_ON_ONCE(master->nr_free < output->nr_chans))
+		return;
+
+	bitmap_allocate_region(&master->chan_map[0], output->channel,
+			       ilog2(output->nr_chans));
+
+	master->nr_free -= output->nr_chans;
+}
+
+static void
+stm_output_disclaim(struct stm_device *stm, struct stm_output *output)
+{
+	struct stp_master *master = stm_master(stm, output->master);
+
+	bitmap_release_region(&master->chan_map[0], output->channel,
+			      ilog2(output->nr_chans));
+
+	master->nr_free += output->nr_chans;
+}
+
+/*
+ * This is like bitmap_find_free_region(), except it can ignore @start bits
+ * at the beginning.
+ */
+static int find_free_channels(unsigned long *bitmap, unsigned int start,
+			      unsigned int end, unsigned int width)
+{
+	unsigned int pos;
+	int i;
+
+	for (pos = start; pos < end + 1; pos = ALIGN(pos, width)) {
+		pos = find_next_zero_bit(bitmap, end + 1, pos);
+		if (pos + width > end + 1)
+			break;
+
+		if (pos & (width - 1))
+			continue;
+
+		for (i = 1; i < width && !test_bit(pos + i, bitmap); i++)
+			;
+		if (i == width)
+			return pos;
+	}
+
+	return -1;
+}
+
+static unsigned int
+stm_find_master_chan(struct stm_device *stm, unsigned int width,
+		     unsigned int *mstart, unsigned int mend,
+		     unsigned int *cstart, unsigned int cend)
+{
+	struct stp_master *master;
+	unsigned int midx;
+	int pos, err;
+
+	for (midx = *mstart; midx <= mend; midx++) {
+		if (!stm_master(stm, midx)) {
+			err = stp_master_alloc(stm, midx);
+			if (err)
+				return err;
+		}
+
+		master = stm_master(stm, midx);
+
+		if (!master->nr_free)
+			continue;
+
+		pos = find_free_channels(master->chan_map, *cstart, cend,
+					 width);
+		if (pos < 0)
+			continue;
+
+		*mstart = midx;
+		*cstart = pos;
+		return 0;
+	}
+
+	return -ENOSPC;
+}
+
+static int stm_output_assign(struct stm_device *stm, unsigned int width,
+			     struct stp_policy_node *policy_node,
+			     struct stm_output *output)
+{
+	unsigned int midx, cidx, mend, cend;
+	int ret = -EBUSY;
+
+	if (width > stm->data->sw_nchannels)
+		return -EINVAL;
+
+	if (policy_node) {
+		stp_policy_node_get_ranges(policy_node,
+					   &midx, &mend, &cidx, &cend);
+	} else {
+		midx = stm->data->sw_start;
+		cidx = 0;
+		mend = stm->data->sw_end;
+		cend = stm->data->sw_nchannels - 1;
+	}
+
+	spin_lock(&stm->mc_lock);
+	if (output->nr_chans)
+		goto unlock;
+
+	ret = stm_find_master_chan(stm, width, &midx, mend, &cidx, cend);
+	if (ret)
+		goto unlock;
+
+	output->master = midx;
+	output->channel = cidx;
+	output->nr_chans = width;
+	stm_output_claim(stm, output);
+	dev_dbg(stm->dev, "assigned %u:%u (+%u)\n", midx, cidx, width);
+
+	ret = 0;
+unlock:
+	spin_unlock(&stm->mc_lock);
+
+	return ret;
+}
+
+static void stm_output_free(struct stm_device *stm, struct stm_output *output)
+{
+	spin_lock(&stm->mc_lock);
+	if (output->nr_chans)
+		stm_output_disclaim(stm, output);
+	spin_unlock(&stm->mc_lock);
+}
+
+static int major_match(struct device *dev, const void *data)
+{
+	unsigned int major = *(unsigned int *)data;
+
+	return MAJOR(dev->devt) == major;
+}
+
+static int stm_char_open(struct inode *inode, struct file *file)
+{
+	struct stm_file *stmf;
+	struct device *dev;
+	unsigned int major = imajor(inode);
+	int err = -ENODEV;
+
+	dev = class_find_device(&stm_class, NULL, &major, major_match);
+	if (!dev)
+		return -ENODEV;
+
+	stmf = kzalloc(sizeof(*stmf), GFP_KERNEL);
+	if (!stmf)
+		return -ENOMEM;
+
+	stmf->stm = dev_get_drvdata(dev);
+
+	if (!try_module_get(stmf->stm->owner))
+		goto err_free;
+
+	file->private_data = stmf;
+
+	return nonseekable_open(inode, file);
+
+err_free:
+	kfree(stmf);
+
+	return err;
+}
+
+static int stm_char_release(struct inode *inode, struct file *file)
+{
+	struct stm_file *stmf = file->private_data;
+
+	stm_output_free(stmf->stm, &stmf->output);
+	module_put(stmf->stm->owner);
+	kfree(stmf);
+
+	return 0;
+}
+
+static int stm_file_assign(struct stm_file *stmf, char *id, unsigned int width)
+{
+	struct stm_device *stm = stmf->stm;
+	int ret;
+
+	mutex_lock(&stm->policy_mutex);
+	if (stm->policy)
+		stmf->policy_node = stp_policy_node_lookup(stm->policy, id);
+
+	ret = stm_output_assign(stm, width, stmf->policy_node, &stmf->output);
+	mutex_unlock(&stm->policy_mutex);
+
+	return ret;
+}
+
+static ssize_t stm_char_write(struct file *file, const char __user *buf,
+			      size_t count, loff_t *ppos)
+{
+	struct stm_file *stmf = file->private_data;
+	struct stm_device *stm = stmf->stm;
+	char *kbuf;
+	int err;
+
+	/*
+	 * if no m/c have been assigned to this writer up to this
+	 * point, use "default" policy entry
+	 */
+	if (!stmf->output.nr_chans) {
+		err = stm_file_assign(stmf, "default", 1);
+		/*
+		 * EBUSY means that somebody else just assigned this
+		 * output, which is just fine for write()
+		 */
+		if (err && err != -EBUSY)
+			return err;
+	}
+
+	kbuf = kmalloc(count + 1, GFP_KERNEL);
+	if (!kbuf)
+		return -ENOMEM;
+
+	err = copy_from_user(kbuf, buf, count);
+	if (err) {
+		kfree(kbuf);
+		return -EFAULT;
+	}
+
+	stm->data->write(stm->data, stmf->output.master,
+			 stmf->output.channel, kbuf, count);
+
+
+	kfree(kbuf);
+
+	return count;
+}
+
+static int stm_char_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct stm_file *stmf = file->private_data;
+	struct stm_device *stm = stmf->stm;
+	unsigned long size, phys;
+
+	if (!stm->data->mmio_addr)
+		return -EOPNOTSUPP;
+
+	if (vma->vm_pgoff)
+		return -EINVAL;
+
+	size = vma->vm_end - vma->vm_start;
+
+	if (stmf->output.nr_chans * stm->data->sw_mmiosz != size)
+		return -EINVAL;
+
+	phys = stm->data->mmio_addr(stm->data, stmf->output.master,
+				    stmf->output.channel,
+				    stmf->output.nr_chans);
+
+	if (!phys)
+		return -EINVAL;
+
+	vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+	vma->vm_flags |= VM_IO | VM_DONTEXPAND | VM_DONTDUMP;
+	vm_iomap_memory(vma, phys, size);
+
+	return 0;
+}
+
+static int stm_char_policy_set_ioctl(struct stm_file *stmf, void __user *arg)
+{
+	struct stm_device *stm = stmf->stm;
+	struct stp_policy_id *id;
+	int ret = -EINVAL;
+	u32 size;
+
+	if (stmf->output.nr_chans)
+		return -EBUSY;
+
+	if (copy_from_user(&size, arg, sizeof(size)))
+		return -EFAULT;
+
+	if (size >= PATH_MAX + sizeof(*id))
+		return -EINVAL;
+
+	/* size + 1 to make sure the .id string at the bottom is terminated */
+	id = kzalloc(size + 1, GFP_KERNEL);
+	if (!id)
+		return -ENOMEM;
+
+	if (copy_from_user(id, arg, size)) {
+		ret = -EFAULT;
+		goto err_free;
+	}
+
+	if (id->__reserved_0 || id->__reserved_1)
+		goto err_free;
+
+	if (id->width < 1 ||
+	    id->width > PAGE_SIZE / stm->data->sw_mmiosz)
+		goto err_free;
+
+	ret = stm_file_assign(stmf, id->id, id->width);
+	if (ret)
+		goto err_free;
+
+	if (stm->data->link)
+		stm->data->link(stm->data, stmf->output.master,
+				stmf->output.channel);
+
+	ret = 0;
+
+err_free:
+	kfree(id);
+
+	return ret;
+}
+
+static int stm_char_policy_get_ioctl(struct stm_file *stmf, void __user *arg)
+{
+	struct stp_policy_id id = {
+		.size		= sizeof(id),
+		.master		= stmf->output.master,
+		.channel	= stmf->output.channel,
+		.width		= stmf->output.nr_chans,
+		.__reserved_0	= 0,
+		.__reserved_1	= 0,
+	};
+
+	return copy_to_user(arg, &id, id.size) ? -EFAULT : 0;
+}
+
+static long
+stm_char_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct stm_file *stmf = file->private_data;
+	struct stm_data *stm_data = stmf->stm->data;
+	int err = -ENOTTY;
+
+	switch (cmd) {
+	case STP_POLICY_ID_SET:
+		err = stm_char_policy_set_ioctl(stmf, (void __user *)arg);
+		if (err)
+			return err;
+
+		return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
+
+	case STP_POLICY_ID_GET:
+		return stm_char_policy_get_ioctl(stmf, (void __user *)arg);
+
+	default:
+		if (stm_data->ioctl)
+			err = stm_data->ioctl(stm_data, cmd, arg);
+
+		break;
+	}
+
+	return err;
+}
+
+#ifdef CONFIG_COMPAT
+static long
+stm_char_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	return stm_char_ioctl(file, cmd, (unsigned long)compat_ptr(arg));
+}
+#else
+#define stm_char_compat_ioctl	NULL
+#endif
+
+static const struct file_operations stm_fops = {
+	.open		= stm_char_open,
+	.release	= stm_char_release,
+	.write		= stm_char_write,
+	.mmap		= stm_char_mmap,
+	.unlocked_ioctl	= stm_char_ioctl,
+	.compat_ioctl	= stm_char_compat_ioctl,
+	.llseek		= no_llseek,
+};
+
+int stm_register_device(struct device *parent, struct stm_data *stm_data,
+			struct module *owner)
+{
+	struct stm_device *stm;
+	struct device *dev;
+	unsigned int nmasters;
+	int err = -ENOMEM;
+
+	if (!stm_core_up)
+		return -EPROBE_DEFER;
+
+	if (!stm_data->write || !stm_data->sw_nchannels)
+		return -EINVAL;
+
+	nmasters = stm_data->sw_end - stm_data->sw_start;
+	stm = kzalloc(sizeof(*stm) + nmasters * sizeof(void *), GFP_KERNEL);
+	if (!stm)
+		return -ENOMEM;
+
+	stm->major = register_chrdev(0, stm_data->name, &stm_fops);
+	if (stm->major < 0)
+		goto err_free;
+
+	dev = device_create(&stm_class, parent, MKDEV(stm->major, 0), NULL,
+			    "%s", stm_data->name);
+	if (IS_ERR(dev)) {
+		err = PTR_ERR(dev);
+		goto err_device;
+	}
+
+	spin_lock_init(&stm->link_lock);
+	INIT_LIST_HEAD(&stm->link_list);
+
+	spin_lock_init(&stm->mc_lock);
+	mutex_init(&stm->policy_mutex);
+	stm->sw_nmasters = nmasters;
+	stm->owner = owner;
+	stm->data = stm_data;
+	stm->dev = dev;
+	stm_data->stm = stm;
+
+	dev_set_drvdata(dev, stm);
+
+	return 0;
+
+err_device:
+	device_unregister(dev);
+err_free:
+	kfree(stm);
+
+	return err;
+}
+EXPORT_SYMBOL_GPL(stm_register_device);
+
+static void stm_source_link_drop(struct stm_source_device *src);
+
+void stm_unregister_device(struct stm_data *stm_data)
+{
+	struct stm_device *stm = stm_data->stm;
+	struct stm_source_device *src, *iter;
+	int i;
+
+	spin_lock(&stm->link_lock);
+	list_for_each_entry_safe(src, iter, &stm->link_list, link_entry) {
+		stm_source_link_drop(src);
+	}
+	spin_unlock(&stm->link_lock);
+
+	synchronize_srcu(&stm_source_srcu);
+
+	unregister_chrdev(stm->major, stm_data->name);
+
+	if (stm->policy)
+		stp_policy_unbind(stm->policy);
+
+	for (i = 0; i < stm->sw_nmasters; i++)
+		stp_master_free(stm, i);
+
+	device_unregister(stm->dev);
+	kfree(stm);
+	stm_data->stm = NULL;
+}
+EXPORT_SYMBOL_GPL(stm_unregister_device);
+
+/**
+ * stm_source_link_add() - connect an stm_source device to an stm device
+ * @src:	stm_source device
+ * @stm:	stm device
+ *
+ * This function establishes a link from stm_source to an stm device so that
+ * the former can send out trace data to the latter.
+ *
+ * Return:	0 on success, -errno otherwise.
+ */
+static int stm_source_link_add(struct stm_source_device *src,
+			       struct stm_device *stm)
+{
+	int err;
+
+	spin_lock(&stm->link_lock);
+	spin_lock(&src->link_lock);
+
+	/* src->link is dereferenced under stm_source_srcu but not the list */
+	rcu_assign_pointer(src->link, stm);
+	list_add_tail(&src->link_entry, &stm->link_list);
+
+	spin_unlock(&src->link_lock);
+	spin_unlock(&stm->link_lock);
+
+	if (stm->policy) {
+		char *id = kstrdup(src->data->name, GFP_KERNEL);
+
+		if (id) {
+			src->policy_node =
+				stp_policy_node_lookup(stm->policy, id);
+
+			kfree(id);
+		}
+	}
+
+	err = stm_output_assign(stm, src->data->nr_chans,
+				src->policy_node, &src->output);
+	if (err)
+		return err;
+
+	/* this is to notify the STM device that a new link has been made */
+	if (stm->data->link)
+		stm->data->link(stm->data, src->output.master,
+				src->output.channel);
+
+	/* this is to let the source carry out all necessary preparations */
+	if (src->data->link)
+		src->data->link(src->data);
+
+	return 0;
+}
+
+/**
+ * stm_source_link_drop() - detach stm_source from its stm device
+ * @src:	stm_source device
+ *
+ * Unlinking means disconnecting from source's STM device; after this
+ * writes will be unsuccessful until it is linked to a new STM device.
+ *
+ * This will happen on "stm_source_link" sysfs attribute write to undo
+ * the existing link (if any), or on linked STM device's de-registration.
+ */
+static void stm_source_link_drop(struct stm_source_device *src)
+{
+	int idx = srcu_read_lock(&stm_source_srcu);
+
+	if (src->link && src->data->unlink)
+		src->data->unlink(src->data);
+
+	srcu_read_unlock(&stm_source_srcu, idx);
+
+	spin_lock(&src->link_lock);
+	if (src->link) {
+		stm_output_free(src->link, &src->output);
+		list_del_init(&src->link_entry);
+		rcu_assign_pointer(src->link, NULL);
+	}
+	spin_unlock(&src->link_lock);
+}
+
+static ssize_t stm_source_link_show(struct device *dev,
+				    struct device_attribute *attr,
+				    char *buf)
+{
+	struct stm_source_device *src = dev_get_drvdata(dev);
+	int idx, ret;
+
+	idx = srcu_read_lock(&stm_source_srcu);
+	ret = sprintf(buf, "%s\n",
+		      src->link ? dev_name(src->link->dev) : "<none>");
+	srcu_read_unlock(&stm_source_srcu, idx);
+
+	return ret;
+}
+
+static ssize_t stm_source_link_store(struct device *dev,
+				     struct device_attribute *attr,
+				     const char *buf, size_t count)
+{
+	struct stm_source_device *src = dev_get_drvdata(dev);
+	struct stm_device *link;
+	struct device *linkdev;
+	int err;
+
+	stm_source_link_drop(src);
+
+	linkdev = stm_find_device(buf, count);
+	if (!linkdev)
+		return -EINVAL;
+
+	link = dev_get_drvdata(linkdev);
+
+	err = stm_source_link_add(src, link);
+
+	return err ? : count;
+}
+
+static DEVICE_ATTR_RW(stm_source_link);
+
+static struct attribute *stm_source_attrs[] = {
+	&dev_attr_stm_source_link.attr,
+	NULL,
+};
+
+static const struct attribute_group stm_source_group = {
+	.attrs	= stm_source_attrs,
+};
+
+static const struct attribute_group *stm_source_groups[] = {
+	&stm_source_group,
+	NULL,
+};
+
+static struct class stm_source_class = {
+	.name		= "stm_source",
+	.dev_groups	= stm_source_groups,
+};
+
+/**
+ * stm_source_register_device() - register an stm_source device
+ * @parent:	parent device
+ * @data:	device description structure
+ *
+ * This will create a device of stm_source class that can write
+ * data to an stm device once linked.
+ *
+ * Return:	0 on success, -errno otherwise.
+ */
+int stm_source_register_device(struct device *parent,
+			       struct stm_source_data *data)
+{
+	struct stm_source_device *src;
+	struct device *dev;
+
+	if (!stm_core_up)
+		return -EPROBE_DEFER;
+
+	src = kzalloc(sizeof(*src), GFP_KERNEL);
+	if (!src)
+		return -ENOMEM;
+
+	dev = device_create(&stm_source_class, parent, MKDEV(0, 0), NULL, "%s",
+			    data->name);
+	if (IS_ERR(dev)) {
+		kfree(src);
+		return PTR_ERR(dev);
+	}
+
+	spin_lock_init(&src->link_lock);
+	INIT_LIST_HEAD(&src->link_entry);
+	src->dev = dev;
+	src->data = data;
+	data->src = src;
+	dev_set_drvdata(dev, src);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(stm_source_register_device);
+
+/**
+ * stm_source_unregister_device() - unregister an stm_source device
+ * @data:	device description that was used to register the device
+ *
+ * This will remove a previously created stm_source device from the system.
+ */
+void stm_source_unregister_device(struct stm_source_data *data)
+{
+	struct stm_source_device *src = data->src;
+
+	stm_source_link_drop(src);
+
+	device_destroy(&stm_source_class, src->dev->devt);
+
+	kfree(src);
+}
+EXPORT_SYMBOL_GPL(stm_source_unregister_device);
+
+int stm_source_write(struct stm_source_data *data, unsigned int chan,
+		     const char *buf, size_t count)
+{
+	struct stm_source_device *src = data->src;
+	struct stm_device *stm;
+	int idx;
+
+	if (!src->output.nr_chans)
+		return -ENODEV;
+
+	if (chan >= src->output.nr_chans)
+		return -EINVAL;
+
+	idx = srcu_read_lock(&stm_source_srcu);
+
+	stm = srcu_dereference(src->link, &stm_source_srcu);
+	if (stm)
+		count = stm->data->write(stm->data, src->output.master,
+					 src->output.channel + chan, buf,
+					 count);
+	else
+		count = -ENODEV;
+
+	srcu_read_unlock(&stm_source_srcu, idx);
+
+	return count;
+}
+EXPORT_SYMBOL_GPL(stm_source_write);
+
+static int __init stm_core_init(void)
+{
+	int err;
+
+	err = class_register(&stm_class);
+	if (err)
+		return err;
+
+	err = class_register(&stm_source_class);
+	if (err)
+		goto err_stm;
+
+	err = stp_configfs_init();
+	if (err)
+		goto err_src;
+
+	init_srcu_struct(&stm_source_srcu);
+
+	stm_core_up++;
+
+	return 0;
+
+err_src:
+	class_unregister(&stm_source_class);
+err_stm:
+	class_unregister(&stm_class);
+
+	return err;
+}
+
+postcore_initcall(stm_core_init);
+
+static void __exit stm_core_exit(void)
+{
+	class_unregister(&stm_source_class);
+	class_unregister(&stm_class);
+	stp_configfs_exit();
+}
+
+module_exit(stm_core_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("System Trace Module device class");
+MODULE_AUTHOR("Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>");
diff --git a/drivers/hwtracing/stm/policy.c b/drivers/hwtracing/stm/policy.c
new file mode 100644
index 0000000000..b5c59a0e0c
--- /dev/null
+++ b/drivers/hwtracing/stm/policy.c
@@ -0,0 +1,467 @@
+/*
+ * System Trace Module (STM) master/channel allocation policy management
+ * Copyright (c) 2014, Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * A master/channel allocation policy allows mapping string identifiers to
+ * master and channel ranges, where allocation can be done.
+ */
+
+#define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
+
+#include <linux/types.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/configfs.h>
+#include <linux/slab.h>
+#include <linux/stm.h>
+#include "stm.h"
+
+/*
+ * STP Master/Channel allocation policy configfs layout.
+ */
+
+struct stp_policy {
+	struct config_group	group;
+	struct stm_device	*stm;
+};
+
+struct stp_policy_node {
+	struct config_group	group;
+	struct stm_device	*stm;
+	struct stp_policy	*policy;
+	unsigned int		first_master;
+	unsigned int		last_master;
+	unsigned int		first_channel;
+	unsigned int		last_channel;
+};
+
+void stp_policy_node_get_ranges(struct stp_policy_node *policy_node,
+				unsigned int *mstart, unsigned int *mend,
+				unsigned int *cstart, unsigned int *cend)
+{
+	*mstart	= policy_node->first_master;
+	*mend	= policy_node->last_master;
+	*cstart	= policy_node->first_channel;
+	*cend	= policy_node->last_channel;
+}
+
+static inline char *stp_policy_node_name(struct stp_policy_node *policy_node)
+{
+	return policy_node->group.cg_item.ci_name ? : "<none>";
+}
+
+static inline struct stp_policy *to_stp_policy(struct config_item *item)
+{
+	return item ?
+		container_of(to_config_group(item), struct stp_policy, group) :
+		NULL;
+}
+
+static inline struct stp_policy_node *
+to_stp_policy_node(struct config_item *item)
+{
+	return item ?
+		container_of(to_config_group(item), struct stp_policy_node,
+			     group) :
+		NULL;
+}
+
+static ssize_t stp_policy_node_masters_show(struct stp_policy_node *policy_node,
+					    char *page)
+{
+	ssize_t count;
+
+	count = sprintf(page, "%u %u\n", policy_node->first_master,
+			policy_node->last_master);
+
+	return count;
+}
+
+static ssize_t
+stp_policy_node_masters_store(struct stp_policy_node *policy_node,
+			      const char *page, size_t count)
+{
+	struct stm_device *stm = policy_node->stm;
+	unsigned int first, last;
+	char *p = (char *) page;
+
+	if (sscanf(p, "%u %u", &first, &last) != 2)
+		return -EINVAL;
+
+	/* must be within [sw_start..sw_end], which is an inclusive range */
+	if (first > INT_MAX || last > INT_MAX || first > last ||
+	    first < stm->data->sw_start ||
+	    last > stm->data->sw_end)
+		return -ERANGE;
+
+	policy_node->first_master = first;
+	policy_node->last_master = last;
+
+	return count;
+}
+
+static ssize_t
+stp_policy_node_channels_show(struct stp_policy_node *policy_node, char *page)
+{
+	ssize_t count;
+
+	count = sprintf(page, "%u %u\n", policy_node->first_channel,
+			policy_node->last_channel);
+
+	return count;
+}
+
+static ssize_t
+stp_policy_node_channels_store(struct stp_policy_node *policy_node,
+			       const char *page, size_t count)
+{
+	unsigned int first, last;
+	char *p = (char *) page;
+
+	if (sscanf(p, "%u %u", &first, &last) != 2)
+		return -EINVAL;
+
+	if (first > INT_MAX || last > INT_MAX || first > last ||
+	    last >= policy_node->stm->data->sw_nchannels)
+		return -ERANGE;
+
+	policy_node->first_channel = first;
+	policy_node->last_channel = last;
+
+	return count;
+}
+
+static void stp_policy_node_release(struct config_item *item)
+{
+	kfree(to_stp_policy_node(item));
+}
+
+struct stp_policy_node_attribute {
+	struct configfs_attribute	attr;
+	ssize_t (*show)(struct stp_policy_node *, char *);
+	ssize_t (*store)(struct stp_policy_node *, const char *, size_t);
+};
+
+static ssize_t stp_policy_node_attr_show(struct config_item *item,
+					 struct configfs_attribute *attr,
+					 char *page)
+{
+	struct stp_policy_node *policy_node = to_stp_policy_node(item);
+	struct stp_policy_node_attribute *pn_attr =
+		container_of(attr, struct stp_policy_node_attribute, attr);
+	ssize_t count = 0;
+
+	if (pn_attr->show)
+		count = pn_attr->show(policy_node, page);
+
+	return count;
+}
+
+static ssize_t stp_policy_node_attr_store(struct config_item *item,
+					  struct configfs_attribute *attr,
+					  const char *page, size_t len)
+{
+	struct stp_policy_node *policy_node = to_stp_policy_node(item);
+	struct stp_policy_node_attribute *pn_attr =
+		container_of(attr, struct stp_policy_node_attribute, attr);
+	ssize_t count = -EINVAL;
+
+	if (pn_attr->store)
+		count = pn_attr->store(policy_node, page, len);
+
+	return count;
+}
+
+static struct configfs_item_operations stp_policy_node_item_ops = {
+	.release		= stp_policy_node_release,
+	.show_attribute		= stp_policy_node_attr_show,
+	.store_attribute	= stp_policy_node_attr_store,
+};
+
+static struct stp_policy_node_attribute stp_policy_node_attr_range = {
+	.attr	= {
+		.ca_owner = THIS_MODULE,
+		.ca_name = "masters",
+		.ca_mode = S_IRUGO | S_IWUSR,
+	},
+	.show	= stp_policy_node_masters_show,
+	.store	= stp_policy_node_masters_store,
+};
+
+static struct stp_policy_node_attribute stp_policy_node_attr_channels = {
+	.attr	= {
+		.ca_owner = THIS_MODULE,
+		.ca_name = "channels",
+		.ca_mode = S_IRUGO | S_IWUSR,
+	},
+	.show	= stp_policy_node_channels_show,
+	.store	= stp_policy_node_channels_store,
+};
+
+static struct configfs_attribute *stp_policy_node_attrs[] = {
+	&stp_policy_node_attr_range.attr,
+	&stp_policy_node_attr_channels.attr,
+	NULL,
+};
+
+static struct config_item_type stp_policy_type;
+static struct config_item_type stp_policy_node_type;
+
+static struct config_group *
+stp_policy_node_make(struct config_group *group, const char *name)
+{
+	struct stp_policy_node *policy_node, *parent_node;
+	struct stp_policy *policy;
+
+	if (group->cg_item.ci_type == &stp_policy_type) {
+		policy = container_of(group, struct stp_policy, group);
+	} else {
+		parent_node = container_of(group, struct stp_policy_node,
+					   group);
+		policy = parent_node->policy;
+	}
+
+	if (!policy->stm)
+		return ERR_PTR(-ENODEV);
+
+	policy_node = kzalloc(sizeof(struct stp_policy_node), GFP_KERNEL);
+	if (!policy_node)
+		return ERR_PTR(-ENOMEM);
+
+	config_group_init_type_name(&policy_node->group, name,
+				    &stp_policy_node_type);
+
+	policy_node->policy = policy;
+	policy_node->stm = policy->stm;
+
+	/* default values for the attributes */
+	policy_node->first_master = policy->stm->data->sw_start;
+	policy_node->last_master = policy->stm->data->sw_end;
+	policy_node->first_channel = 0;
+	policy_node->last_channel = policy->stm->data->sw_nchannels - 1;
+
+	return &policy_node->group;
+}
+
+static void
+stp_policy_node_drop(struct config_group *group, struct config_item *item)
+{
+	config_item_put(item);
+}
+
+static struct configfs_group_operations stp_policy_node_group_ops = {
+	.make_group	= stp_policy_node_make,
+	.drop_item	= stp_policy_node_drop,
+};
+
+static struct config_item_type stp_policy_node_type = {
+	.ct_item_ops	= &stp_policy_node_item_ops,
+	.ct_group_ops	= &stp_policy_node_group_ops,
+	.ct_attrs	= stp_policy_node_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+/*
+ * Root group: policies.
+ */
+static struct configfs_attribute stp_policy_attr_device = {
+	.ca_owner = THIS_MODULE,
+	.ca_name = "device",
+	.ca_mode = S_IRUGO | S_IWUSR,
+};
+
+static struct configfs_attribute *stp_policy_attrs[] = {
+	&stp_policy_attr_device,
+	NULL,
+};
+
+static ssize_t stp_policy_attr_show(struct config_item *item,
+				    struct configfs_attribute *attr,
+				    char *page)
+{
+	struct stp_policy *policy = to_stp_policy(item);
+
+	return sprintf(page, "%s\n",
+		       (policy && policy->stm) ?
+		       policy->stm->data->name :
+		       "<none>");
+}
+
+static ssize_t stp_policy_attr_store(struct config_item *item,
+				     struct configfs_attribute *attr,
+				     const char *page, size_t len)
+{
+	struct stp_policy *policy = to_stp_policy(item);
+	ssize_t count = -EINVAL;
+	struct device *dev;
+
+	dev = stm_find_device(page, len);
+	if (dev) {
+		count = len;
+		if (policy->stm)
+			put_device(policy->stm->dev);
+
+		policy->stm = dev_get_drvdata(dev);
+
+		mutex_lock(&policy->stm->policy_mutex);
+		policy->stm->policy = policy;
+		mutex_unlock(&policy->stm->policy_mutex);
+	}
+
+	return count;
+}
+
+void stp_policy_unbind(struct stp_policy *policy)
+{
+	put_device(policy->stm->dev);
+
+	mutex_lock(&policy->stm->policy_mutex);
+	policy->stm->policy = NULL;
+	mutex_unlock(&policy->stm->policy_mutex);
+
+	policy->stm = NULL;
+}
+
+static void stp_policy_release(struct config_item *item)
+{
+	struct stp_policy *policy = to_stp_policy(item);
+
+	stp_policy_unbind(policy);
+	kfree(policy);
+}
+
+static struct configfs_item_operations stp_policy_item_ops = {
+	.release		= stp_policy_release,
+	.show_attribute		= stp_policy_attr_show,
+	.store_attribute	= stp_policy_attr_store,
+};
+
+static struct configfs_group_operations stp_policy_group_ops = {
+	.make_group	= stp_policy_node_make,
+};
+
+static struct config_item_type stp_policy_type = {
+	.ct_item_ops	= &stp_policy_item_ops,
+	.ct_group_ops	= &stp_policy_group_ops,
+	.ct_attrs	= stp_policy_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct config_group *
+stp_policies_make(struct config_group *group, const char *name)
+{
+	struct stp_policy *policy;
+
+	policy = kzalloc(sizeof(*policy), GFP_KERNEL);
+	if (!policy)
+		return ERR_PTR(-ENOMEM);
+
+	config_group_init_type_name(&policy->group, name,
+				    &stp_policy_type);
+	policy->stm = NULL;
+
+	return &policy->group;
+}
+
+static struct configfs_group_operations stp_policies_group_ops = {
+	.make_group	= stp_policies_make,
+};
+
+static struct config_item_type stp_policies_type = {
+	.ct_group_ops	= &stp_policies_group_ops,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct configfs_subsystem stp_policy_subsys = {
+	.su_group = {
+		.cg_item = {
+			.ci_namebuf	= "stp-policy",
+			.ci_type	= &stp_policies_type,
+		},
+	},
+};
+
+/*
+ * Lock the policy mutex from the outside
+ */
+static struct stp_policy_node *
+__stp_policy_node_lookup(struct stp_policy *policy, char *s)
+{
+	struct stp_policy_node *policy_node, *ret;
+	struct list_head *head = &policy->group.cg_children;
+	struct config_item *item;
+	char *start, *end = s;
+
+	if (list_empty(head))
+		return NULL;
+
+	/* return the first entry if everything else fails */
+	item = list_entry(head->next, struct config_item, ci_entry);
+	ret = to_stp_policy_node(item);
+
+next:
+	for (;;) {
+		start = strsep(&end, "/");
+		if (!start)
+			break;
+
+		if (!*start)
+			continue;
+
+		list_for_each_entry(item, head, ci_entry) {
+			policy_node = to_stp_policy_node(item);
+
+			if (!strcmp(start,
+				    policy_node->group.cg_item.ci_name)) {
+				ret = policy_node;
+
+				if (!end)
+					goto out;
+
+				head = &policy_node->group.cg_children;
+				goto next;
+			}
+		}
+		break;
+	}
+
+out:
+	return ret;
+}
+
+struct stp_policy_node *
+stp_policy_node_lookup(struct stp_policy *policy, char *s)
+{
+	struct stp_policy_node *policy_node;
+
+	mutex_lock(&stp_policy_subsys.su_mutex);
+	policy_node = __stp_policy_node_lookup(policy, s);
+	mutex_unlock(&stp_policy_subsys.su_mutex);
+
+	return policy_node;
+}
+
+int __init stp_configfs_init(void)
+{
+	int err;
+
+	config_group_init(&stp_policy_subsys.su_group);
+	mutex_init(&stp_policy_subsys.su_mutex);
+	err = configfs_register_subsystem(&stp_policy_subsys);
+
+	return err;
+}
+
+void __exit stp_configfs_exit(void)
+{
+	configfs_unregister_subsystem(&stp_policy_subsys);
+}
diff --git a/drivers/hwtracing/stm/stm.h b/drivers/hwtracing/stm/stm.h
new file mode 100644
index 0000000000..4d088a1400
--- /dev/null
+++ b/drivers/hwtracing/stm/stm.h
@@ -0,0 +1,79 @@
+/*
+ * System Trace Module (STM) infrastructure
+ * Copyright (c) 2014, Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * STM class implements generic infrastructure for  System Trace Module devices
+ * as defined in MIPI STPv2 specification.
+ */
+
+#ifndef _CLASS_STM_H_
+#define _CLASS_STM_H_
+
+struct stp_policy;
+struct stp_policy_node;
+
+struct stp_policy_node *
+stp_policy_node_lookup(struct stp_policy *policy, char *s);
+void stp_policy_unbind(struct stp_policy *policy);
+
+void stp_policy_node_get_ranges(struct stp_policy_node *policy_node,
+				unsigned int *mstart, unsigned int *mend,
+				unsigned int *cstart, unsigned int *cend);
+int stp_configfs_init(void);
+void stp_configfs_exit(void);
+
+struct stp_master {
+	unsigned int	nr_free;
+	unsigned long	chan_map[0];
+};
+
+struct stm_device {
+	struct device		*dev;
+	struct module		*owner;
+	struct stp_policy	*policy;
+	struct mutex		policy_mutex;
+	int			major;
+	unsigned int		sw_nmasters;
+	struct stm_data		*data;
+	spinlock_t		link_lock;
+	struct list_head	link_list;
+	/* master allocation */
+	spinlock_t		mc_lock;
+	struct stp_master	*masters[0];
+};
+
+struct stm_output {
+	unsigned int		master;
+	unsigned int		channel;
+	unsigned int		nr_chans;
+};
+
+struct stm_file {
+	struct stm_device	*stm;
+	struct stp_policy_node	*policy_node;
+	struct stm_output	output;
+};
+
+struct device *stm_find_device(const char *name, size_t len);
+
+struct stm_source_device {
+	struct device		*dev;
+	struct stm_source_data	*data;
+	spinlock_t		link_lock;
+	struct stm_device	*link;
+	struct list_head	link_entry;
+	/* one output per stm_source device */
+	struct stp_policy_node	*policy_node;
+	struct stm_output	output;
+};
+
+#endif /* _CLASS_STM_H_ */
diff --git a/include/linux/stm.h b/include/linux/stm.h
new file mode 100644
index 0000000000..976c94d8f1
--- /dev/null
+++ b/include/linux/stm.h
@@ -0,0 +1,102 @@
+/*
+ * System Trace Module (STM) infrastructure apis
+ * Copyright (C) 2014 Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+
+#ifndef _STM_H_
+#define _STM_H_
+
+#include <linux/device.h>
+
+struct stp_policy;
+
+struct stm_device;
+
+/**
+ * struct stm_data - STM device description and callbacks
+ * @name:		device name
+ * @stm:		internal structure, only used by stm class code
+ * @sw_start:		first STP master available to software
+ * @sw_end:		last STP master available to software
+ * @sw_nchannels:	number of STP channels per master
+ * @sw_mmiosz:		size of one channel's IO space, for mmap, optional
+ * @write:		write callback
+ * @mmio_addr:		mmap callback, optional
+ * @link:		called when a new stm_source gets linked to us, optional
+ * @unlink:		likewise for unlinking, again optional
+ * @ioctl:		ioctl callback for device-specific commands
+ *
+ * Fill out this structure before calling stm_register_device() to create
+ * an STM device and stm_unregister_device() to destroy it. It will also be
+ * passed back to @write(), @mmio_addr(), @link(), @unlink() and @ioctl()
+ * callbacks.
+ *
+ * Normally, an STM device will have a range of masters available to software
+ * and the rest being statically assigned to various hardware trace sources.
+ * The former is defined by the the range [@sw_start..@sw_end] of the device
+ * description. That is, the lowest master that can be allocated to software
+ * writers is @sw_start and data from this writer will appear is @sw_start
+ * master in the STP stream.
+ */
+struct stm_data {
+	const char		*name;
+	struct stm_device	*stm;
+	unsigned int		sw_start;
+	unsigned int		sw_end;
+	unsigned int		sw_nchannels;
+	unsigned int		sw_mmiosz;
+	ssize_t			(*write)(struct stm_data *, unsigned int,
+					 unsigned int, const char *, size_t);
+	phys_addr_t		(*mmio_addr)(struct stm_data *, unsigned int,
+					     unsigned int, unsigned int);
+	void			(*link)(struct stm_data *, unsigned int,
+					unsigned int);
+	void			(*unlink)(struct stm_data *, unsigned int,
+					  unsigned int);
+	long			(*ioctl)(struct stm_data *, unsigned int,
+					 unsigned long);
+};
+
+int stm_register_device(struct device *parent, struct stm_data *stm_data,
+			struct module *owner);
+void stm_unregister_device(struct stm_data *stm_data);
+
+struct stm_source_device;
+
+/**
+ * struct stm_source_data - STM source device description and callbacks
+ * @name:	device name, will be used for policy lookup
+ * @src:	internal structure, only used by stm class code
+ * @nr_chans:	number of channels to allocate
+ * @link:	called when this source gets linked to an STM device
+ * @unlink:	called when this source is about to get unlinked from its STM
+ *
+ * Fill in this structure before calling stm_source_register_device() to
+ * register a source device. Also pass it to unregister and write calls.
+ */
+struct stm_source_data {
+	const char		*name;
+	struct stm_source_device *src;
+	unsigned int		percpu;
+	unsigned int		nr_chans;
+	int			(*link)(struct stm_source_data *data);
+	void			(*unlink)(struct stm_source_data *data);
+};
+
+int stm_source_register_device(struct device *parent,
+			       struct stm_source_data *data);
+void stm_source_unregister_device(struct stm_source_data *data);
+
+int stm_source_write(struct stm_source_data *data, unsigned int chan,
+		     const char *buf, size_t count);
+
+#endif /* _STM_H_ */
diff --git a/include/uapi/linux/stm.h b/include/uapi/linux/stm.h
new file mode 100644
index 0000000000..042b58b53b
--- /dev/null
+++ b/include/uapi/linux/stm.h
@@ -0,0 +1,47 @@
+/*
+ * System Trace Module (STM) userspace interfaces
+ * Copyright (c) 2014, Intel Corporation.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * STM class implements generic infrastructure for  System Trace Module devices
+ * as defined in MIPI STPv2 specification.
+ */
+
+#ifndef _UAPI_LINUX_STM_H
+#define _UAPI_LINUX_STM_H
+
+/**
+ * struct stp_policy_id - identification for the STP policy
+ * @size:	size of the structure including real id[] length
+ * @master:	assigned master
+ * @channel:	first assigned channel
+ * @width:	number of requested channels
+ * @id:		identification string
+ *
+ * User must calculate the total size of the structure and put it into
+ * @size field, fill out the @id and desired @width. In return, kernel
+ * fills out @master, @channel and @width.
+ */
+struct stp_policy_id {
+	__u32		size;
+	__u16		master;
+	__u16		channel;
+	__u16		width;
+	/* padding */
+	__u16		__reserved_0;
+	__u32		__reserved_1;
+	char		id[0];
+};
+
+#define STP_POLICY_ID_SET	_IOWR('%', 0, struct stp_policy_id)
+#define STP_POLICY_ID_GET	_IOR('%', 1, struct stp_policy_id)
+
+#endif /* _UAPI_LINUX_STM_H */
-- 
2.1.4

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