[PATCH v9 2/2] drivers/misc: Add Aspeed P2A control driver

[Patrick Venture]

The ASPEED AST2400, and AST2500 in some configurations include a
PCI-to-AHB MMIO bridge.  This bridge allows a server to read and write
in the BMC's physical address space.  This feature is especially useful
when using this bridge to send large files to the BMC.

The host may use this to send down a firmware image by staging data at a
specific memory address, and in a coordinated effort with the BMC's
software stack and kernel, transmit the bytes.

This driver enables the BMC to unlock the PCI bridge on demand, and
configure it via ioctl to allow the host to write bytes to an agreed
upon location.  In the primary use-case, the region to use is known
apriori on the BMC, and the host requests this information.  Once this
request is received, the BMC's software stack will enable the bridge and
the region and then using some software flow control (possibly via IPMI
packets), copy the bytes down.  Once the process is complete, the BMC
will disable the bridge and unset any region involved.

The default behavior of this bridge when present is: enabled and all
regions marked read-write.  This driver will fix the regions to be
read-only and then disable the bridge entirely.

The memory regions protected are:
 * BMC flash MMIO window
 * System flash MMIO windows
 * SOC IO (peripheral MMIO)
 * DRAM

The DRAM region itself is all of DRAM and cannot be further specified.
Once the PCI bridge is enabled, the host can read all of DRAM, and if
the DRAM section is write-enabled, then it can write to all of it.

Signed-off-by: Patrick Venture <venture@xxxxxxxxxx>
Reviewed-by: Andrew Jeffery <andrew@xxxxxxxx>
---
Changes for v9:
 - Stop zeroing out memory that is already zeroed out.
Changes for v8:
 - Promoted u32 address values to u64 to be compatible with either.
Changes for v7:
- Moved node under the syscon node and changed therefore how it grabs the phandle for the regmap.
Changes for v6:
- Cleaned up documentation
- Added missing machine-readable copyright lines.
- Fixed over 80 chars instances.
- Changed error from invalid memory-region node to ENODEV.
Changes for v5:
- Fixup missing exit condition and remove extra jump.
Changes for v4:
- Added ioctl for reading back the memory-region configuration.
- Cleaned up some unused variables.
Changes for v3:
- Deleted unused read and write methods.
Changes for v2:
- Dropped unused reads.
- Moved call to disable bridge to before registering device.
- Switch from using regs to using a syscon regmap. <<< IN PROGRESS
- Updated the commit message. <<< TODO
- Updated the bit flipped for SCU180_ENP2A
- Dropped boolean region_specified variable.
- Renamed p2a_ctrl in _probe to misc_ctrl per suggestion.
- Renamed aspeed_p2a_region_search to aspeed_p2a_region_acquire
- Updated commit message.
---
 drivers/misc/Kconfig                 |   8 +
 drivers/misc/Makefile                |   1 +
 drivers/misc/aspeed-p2a-ctrl.c       | 443 +++++++++++++++++++++++++++
 include/uapi/linux/aspeed-p2a-ctrl.h |  62 ++++
 4 files changed, 514 insertions(+)
 create mode 100644 drivers/misc/aspeed-p2a-ctrl.c
 create mode 100644 include/uapi/linux/aspeed-p2a-ctrl.h

diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig
index 42ab8ec92a046..3209ee020b153 100644
--- a/drivers/misc/Kconfig
+++ b/drivers/misc/Kconfig
@@ -496,6 +496,14 @@ config VEXPRESS_SYSCFG
 	  bus. System Configuration interface is one of the possible means
 	  of generating transactions on this bus.
 
+config ASPEED_P2A_CTRL
+	depends on (ARCH_ASPEED || COMPILE_TEST) && REGMAP && MFD_SYSCON
+	tristate "Aspeed ast2400/2500 HOST P2A VGA MMIO to BMC bridge control"
+	help
+	  Control Aspeed ast2400/2500 HOST P2A VGA MMIO to BMC mappings through
+	  ioctl()s, the driver also provides an interface for userspace mappings to
+	  a pre-defined region.
+
 config ASPEED_LPC_CTRL
 	depends on (ARCH_ASPEED || COMPILE_TEST) && REGMAP && MFD_SYSCON
 	tristate "Aspeed ast2400/2500 HOST LPC to BMC bridge control"
diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile
index d5b7d3404dc78..c36239573a5ca 100644
--- a/drivers/misc/Makefile
+++ b/drivers/misc/Makefile
@@ -56,6 +56,7 @@ obj-$(CONFIG_VEXPRESS_SYSCFG)	+= vexpress-syscfg.o
 obj-$(CONFIG_CXL_BASE)		+= cxl/
 obj-$(CONFIG_ASPEED_LPC_CTRL)	+= aspeed-lpc-ctrl.o
 obj-$(CONFIG_ASPEED_LPC_SNOOP)	+= aspeed-lpc-snoop.o
+obj-$(CONFIG_ASPEED_P2A_CTRL)	+= aspeed-p2a-ctrl.o
 obj-$(CONFIG_PCI_ENDPOINT_TEST)	+= pci_endpoint_test.o
 obj-$(CONFIG_OCXL)		+= ocxl/
 obj-y				+= cardreader/
diff --git a/drivers/misc/aspeed-p2a-ctrl.c b/drivers/misc/aspeed-p2a-ctrl.c
new file mode 100644
index 0000000000000..c0521b2ffc6ac
--- /dev/null
+++ b/drivers/misc/aspeed-p2a-ctrl.c
@@ -0,0 +1,443 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2019 Google Inc
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ * Provides a simple driver to control the ASPEED P2A interface which allows
+ * the host to read and write to various regions of the BMC's memory.
+ */
+
+#include <linux/fs.h>
+#include <linux/io.h>
+#include <linux/mfd/syscon.h>
+#include <linux/miscdevice.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of_address.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+
+#include <linux/aspeed-p2a-ctrl.h>
+
+#define DEVICE_NAME	"aspeed-p2a-ctrl"
+
+/* SCU2C is a Misc. Control Register. */
+#define SCU2C 0x2c
+/* SCU180 is the PCIe Configuration Setting Control Register. */
+#define SCU180 0x180
+/* Bit 1 controls the P2A bridge, while bit 0 controls the entire VGA device
+ * on the PCI bus.
+ */
+#define SCU180_ENP2A BIT(1)
+
+/* The ast2400/2500 both have six ranges. */
+#define P2A_REGION_COUNT 6
+
+struct region {
+	u64 min;
+	u64 max;
+	u32 bit;
+};
+
+struct aspeed_p2a_model_data {
+	/* min, max, bit */
+	struct region regions[P2A_REGION_COUNT];
+};
+
+struct aspeed_p2a_ctrl {
+	struct miscdevice miscdev;
+	struct regmap *regmap;
+
+	const struct aspeed_p2a_model_data *config;
+
+	/* Access to these needs to be locked, held via probe, mapping ioctl,
+	 * and release, remove.
+	 */
+	struct mutex tracking;
+	u32 readers;
+	u32 readerwriters[P2A_REGION_COUNT];
+
+	phys_addr_t mem_base;
+	resource_size_t mem_size;
+};
+
+struct aspeed_p2a_user {
+	struct file *file;
+	struct aspeed_p2a_ctrl *parent;
+
+	/* The entire memory space is opened for reading once the bridge is
+	 * enabled, therefore this needs only to be tracked once per user.
+	 * If any user has it open for read, the bridge must stay enabled.
+	 */
+	u32 read;
+
+	/* Each entry of the array corresponds to a P2A Region.  If the user
+	 * opens for read or readwrite, the reference goes up here.  On
+	 * release, this array is walked and references adjusted accordingly.
+	 */
+	u32 readwrite[P2A_REGION_COUNT];
+};
+
+static void aspeed_p2a_enable_bridge(struct aspeed_p2a_ctrl *p2a_ctrl)
+{
+	regmap_update_bits(p2a_ctrl->regmap,
+		SCU180, SCU180_ENP2A, SCU180_ENP2A);
+}
+
+static void aspeed_p2a_disable_bridge(struct aspeed_p2a_ctrl *p2a_ctrl)
+{
+	regmap_update_bits(p2a_ctrl->regmap, SCU180, SCU180_ENP2A, 0);
+}
+
+static int aspeed_p2a_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct aspeed_p2a_user *priv = file->private_data;
+	struct aspeed_p2a_ctrl *ctrl = priv->parent;
+
+	if (ctrl->mem_base == 0 && ctrl->mem_size == 0)
+		return -EINVAL;
+
+	unsigned long vsize = vma->vm_end - vma->vm_start;
+	pgprot_t prot = vma->vm_page_prot;
+
+	if (vma->vm_pgoff + vsize > ctrl->mem_base + ctrl->mem_size)
+		return -EINVAL;
+
+	/* ast2400/2500 AHB accesses are not cache coherent */
+	prot = pgprot_noncached(prot);
+
+	if (remap_pfn_range(vma, vma->vm_start,
+		(ctrl->mem_base >> PAGE_SHIFT) + vma->vm_pgoff,
+		vsize, prot))
+		return -EAGAIN;
+
+	return 0;
+}
+
+static bool aspeed_p2a_region_acquire(struct aspeed_p2a_user *priv,
+		struct aspeed_p2a_ctrl *ctrl,
+		struct aspeed_p2a_ctrl_mapping *map)
+{
+	int i;
+	u64 base, end;
+	bool matched = false;
+
+	base = map->addr;
+	end = map->addr + (map->length - 1);
+
+	/* If the value is a legal u32, it will find a match. */
+	for (i = 0; i < P2A_REGION_COUNT; i++) {
+		const struct region *curr = &ctrl->config->regions[i];
+
+		/* If the top of this region is lower than your base, skip it.
+		 */
+		if (curr->max < base)
+			continue;
+
+		/* If the bottom of this region is higher than your end, bail.
+		 */
+		if (curr->min > end)
+			break;
+
+		/* Lock this and update it, therefore it someone else is
+		 * closing their file out, this'll preserve the increment.
+		 */
+		mutex_lock(&ctrl->tracking);
+		ctrl->readerwriters[i] += 1;
+		mutex_unlock(&ctrl->tracking);
+
+		/* Track with the user, so when they close their file, we can
+		 * decrement properly.
+		 */
+		priv->readwrite[i] += 1;
+
+		/* Enable the region as read-write. */
+		regmap_update_bits(ctrl->regmap, SCU2C, curr->bit, 0);
+		matched = true;
+	}
+
+	return matched;
+}
+
+static long aspeed_p2a_ioctl(struct file *file, unsigned int cmd,
+		unsigned long data)
+{
+	struct aspeed_p2a_user *priv = file->private_data;
+	struct aspeed_p2a_ctrl *ctrl = priv->parent;
+	void __user *arg = (void __user *)data;
+	struct aspeed_p2a_ctrl_mapping map;
+
+	if (copy_from_user(&map, arg, sizeof(map)))
+		return -EFAULT;
+
+	switch (cmd) {
+	case ASPEED_P2A_CTRL_IOCTL_SET_WINDOW:
+		/* If they want a region to be read-only, since the entire
+		 * region is read-only once enabled, we just need to track this
+		 * user wants to read from the bridge, and if it's not enabled.
+		 * Enable it.
+		 */
+		if (map.flags == ASPEED_P2A_CTRL_READ_ONLY) {
+			mutex_lock(&ctrl->tracking);
+			ctrl->readers += 1;
+			mutex_unlock(&ctrl->tracking);
+
+			/* Track with the user, so when they close their file,
+			 * we can decrement properly.
+			 */
+			priv->read += 1;
+		} else if (map.flags == ASPEED_P2A_CTRL_READWRITE) {
+			/* If we don't acquire any region return error. */
+			if (!aspeed_p2a_region_acquire(priv, ctrl, &map)) {
+				return -EINVAL;
+			}
+		} else {
+			/* Invalid map flags. */
+			return -EINVAL;
+		}
+
+		aspeed_p2a_enable_bridge(ctrl);
+		return 0;
+	case ASPEED_P2A_CTRL_IOCTL_GET_MEMORY_CONFIG:
+		/* This is a request for the memory-region and corresponding
+		 * length that is used by the driver for mmap.
+		 */
+
+		map.flags = 0;
+		map.addr = ctrl->mem_base;
+		map.length = ctrl->mem_size;
+
+		return copy_to_user(arg, &map, sizeof(map)) ? -EFAULT : 0;
+	}
+
+	return -EINVAL;
+}
+
+
+/*
+ * When a user opens this file, we create a structure to track their mappings.
+ *
+ * A user can map a region as read-only (bridge enabled), or read-write (bit
+ * flipped, and bridge enabled).  Either way, this tracking is used, s.t. when
+ * they release the device references are handled.
+ *
+ * The bridge is not enabled until a user calls an ioctl to map a region,
+ * simply opening the device does not enable it.
+ */
+static int aspeed_p2a_open(struct inode *inode, struct file *file)
+{
+	struct aspeed_p2a_user *priv;
+
+	priv = kmalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->file = file;
+	priv->read = 0;
+	memset(priv->readwrite, 0, sizeof(priv->readwrite));
+
+	/* The file's private_data is initialized to the p2a_ctrl. */
+	priv->parent = file->private_data;
+
+	/* Set the file's private_data to the user's data. */
+	file->private_data = priv;
+
+	return 0;
+}
+
+/*
+ * This will close the users mappings.  It will go through what they had opened
+ * for readwrite, and decrement those counts.  If at the end, this is the last
+ * user, it'll close the bridge.
+ */
+static int aspeed_p2a_release(struct inode *inode, struct file *file)
+{
+	int i;
+	u32 value;
+	u32 bits = 0;
+	bool open_regions = false;
+	struct aspeed_p2a_user *priv = file->private_data;
+
+	/* Lock others from changing these values until everything is updated
+	 * in one pass.
+	 */
+	mutex_lock(&priv->parent->tracking);
+
+	priv->parent->readers -= priv->read;
+
+	for (i = 0; i < P2A_REGION_COUNT; i++) {
+		priv->parent->readerwriters[i] -= priv->readwrite[i];
+
+		if (priv->parent->readerwriters[i] > 0)
+			open_regions = true;
+		else
+			bits |= priv->parent->config->regions[i].bit;
+	}
+
+	/* Setting a bit to 1 disables the region, so let's just OR with the
+	 * above to disable any.
+	 */
+
+	/* Note, if another user is trying to ioctl, they can't grab tracking,
+	 * and therefore can't grab either register mutex.
+	 * If another user is trying to close, they can't grab tracking either.
+	 */
+	regmap_update_bits(priv->parent->regmap, SCU2C, bits, bits);
+
+	/* If parent->readers is zero and open windows is 0, disable the
+	 * bridge.
+	 */
+	if (!open_regions && priv->parent->readers == 0)
+		aspeed_p2a_disable_bridge(priv->parent);
+
+	mutex_unlock(&priv->parent->tracking);
+
+	kfree(priv);
+
+	return 0;
+}
+
+static const struct file_operations aspeed_p2a_ctrl_fops = {
+	.owner = THIS_MODULE,
+	.mmap = aspeed_p2a_mmap,
+	.unlocked_ioctl = aspeed_p2a_ioctl,
+	.open = aspeed_p2a_open,
+	.release = aspeed_p2a_release,
+};
+
+/* The regions are controlled by SCU2C */
+static void aspeed_p2a_disable_all(struct aspeed_p2a_ctrl *p2a_ctrl)
+{
+	int i;
+	u32 value = 0;
+
+	for (i = 0; i < P2A_REGION_COUNT; i++)
+		value |= p2a_ctrl->config->regions[i].bit;
+
+	regmap_update_bits(p2a_ctrl->regmap, SCU2C, value, value);
+
+	/* Disable the bridge. */
+	aspeed_p2a_disable_bridge(p2a_ctrl);
+}
+
+static int aspeed_p2a_ctrl_probe(struct platform_device *pdev)
+{
+	struct aspeed_p2a_ctrl *misc_ctrl;
+	struct device *dev;
+	struct resource *res, resm;
+	struct device_node *node;
+	int rc = 0;
+
+	dev = &pdev->dev;
+
+	misc_ctrl = devm_kzalloc(dev, sizeof(*misc_ctrl), GFP_KERNEL);
+	if (!misc_ctrl)
+		return -ENOMEM;
+
+	mutex_init(&misc_ctrl->tracking);
+
+	/* optional. */
+	node = of_parse_phandle(dev->of_node, "memory-region", 0);
+	if (node) {
+		rc = of_address_to_resource(node, 0, &resm);
+		of_node_put(node);
+		if (rc) {
+			dev_err(dev, "Couldn't address to resource for reserved memory\n");
+			return -ENODEV;
+		}
+
+		misc_ctrl->mem_size = resource_size(&resm);
+		misc_ctrl->mem_base = resm.start;
+	}
+
+	misc_ctrl->regmap = syscon_node_to_regmap(pdev->dev.parent->of_node);
+	if (IS_ERR(misc_ctrl->regmap)) {
+		dev_err(dev, "Couldn't get regmap\n");
+		return -ENODEV;
+	}
+
+	misc_ctrl->config = of_device_get_match_data(dev);
+
+	dev_set_drvdata(&pdev->dev, misc_ctrl);
+
+	aspeed_p2a_disable_all(misc_ctrl);
+
+	misc_ctrl->miscdev.minor = MISC_DYNAMIC_MINOR;
+	misc_ctrl->miscdev.name = DEVICE_NAME;
+	misc_ctrl->miscdev.fops = &aspeed_p2a_ctrl_fops;
+	misc_ctrl->miscdev.parent = dev;
+
+	rc = misc_register(&misc_ctrl->miscdev);
+	if (rc)
+		dev_err(dev, "Unable to register device\n");
+
+	return rc;
+}
+
+static int aspeed_p2a_ctrl_remove(struct platform_device *pdev)
+{
+	struct aspeed_p2a_ctrl *p2a_ctrl = dev_get_drvdata(&pdev->dev);
+
+	misc_deregister(&p2a_ctrl->miscdev);
+
+	return 0;
+}
+
+#define SCU2C_DRAM	BIT(25)
+#define SCU2C_SPI	BIT(24)
+#define SCU2C_SOC	BIT(23)
+#define SCU2C_FLASH	BIT(22)
+
+static const struct aspeed_p2a_model_data ast2400_model_data = {
+	.regions = {
+		{0x00000000, 0x17FFFFFF, SCU2C_FLASH},
+		{0x18000000, 0x1FFFFFFF, SCU2C_SOC},
+		{0x20000000, 0x2FFFFFFF, SCU2C_FLASH},
+		{0x30000000, 0x3FFFFFFF, SCU2C_SPI},
+		{0x40000000, 0x5FFFFFFF, SCU2C_DRAM},
+		{0x60000000, 0xFFFFFFFF, SCU2C_SOC},
+	}
+};
+
+static const struct aspeed_p2a_model_data ast2500_model_data = {
+	.regions = {
+		{0x00000000, 0x0FFFFFFF, SCU2C_FLASH},
+		{0x10000000, 0x1FFFFFFF, SCU2C_SOC},
+		{0x20000000, 0x3FFFFFFF, SCU2C_FLASH},
+		{0x40000000, 0x5FFFFFFF, SCU2C_SOC},
+		{0x60000000, 0x7FFFFFFF, SCU2C_SPI},
+		{0x80000000, 0xFFFFFFFF, SCU2C_DRAM},
+	}
+};
+
+static const struct of_device_id aspeed_p2a_ctrl_match[] = {
+	{ .compatible = "aspeed,ast2400-p2a-ctrl",
+	  .data = &ast2400_model_data },
+	{ .compatible = "aspeed,ast2500-p2a-ctrl",
+	  .data = &ast2500_model_data },
+	{ },
+};
+
+static struct platform_driver aspeed_p2a_ctrl_driver = {
+	.driver = {
+		.name		= DEVICE_NAME,
+		.of_match_table = aspeed_p2a_ctrl_match,
+	},
+	.probe = aspeed_p2a_ctrl_probe,
+	.remove = aspeed_p2a_ctrl_remove,
+};
+
+module_platform_driver(aspeed_p2a_ctrl_driver);
+
+MODULE_DEVICE_TABLE(of, aspeed_p2a_ctrl_match);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Patrick Venture <venture@xxxxxxxxxx>");
+MODULE_DESCRIPTION("Control for aspeed 2400/2500 P2A VGA HOST to BMC mappings");
diff --git a/include/uapi/linux/aspeed-p2a-ctrl.h b/include/uapi/linux/aspeed-p2a-ctrl.h
new file mode 100644
index 0000000000000..033355552a6e3
--- /dev/null
+++ b/include/uapi/linux/aspeed-p2a-ctrl.h
@@ -0,0 +1,62 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * Copyright 2019 Google Inc
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ * Provides a simple driver to control the ASPEED P2A interface which allows
+ * the host to read and write to various regions of the BMC's memory.
+ */
+
+#ifndef _UAPI_LINUX_ASPEED_P2A_CTRL_H
+#define _UAPI_LINUX_ASPEED_P2A_CTRL_H
+
+#include <linux/ioctl.h>
+#include <linux/types.h>
+
+#define ASPEED_P2A_CTRL_READ_ONLY 0
+#define ASPEED_P2A_CTRL_READWRITE 1
+
+/*
+ * This driver provides a mechanism for enabling or disabling the read-write
+ * property of specific windows into the ASPEED BMC's memory.
+ *
+ * A user can map a region of the BMC's memory as read-only or read-write, with
+ * the caveat that once any region is mapped, all regions are unlocked for
+ * reading.
+ */
+
+/*
+ * Unlock a region of BMC physical memory for access from the host.
+ *
+ * Also used to read back the optional memory-region configuration for the
+ * driver.
+ */
+struct aspeed_p2a_ctrl_mapping {
+	__u64 addr;
+	__u32 length;
+	__u32 flags;
+};
+
+#define __ASPEED_P2A_CTRL_IOCTL_MAGIC 0xb3
+
+/*
+ * This IOCTL is meant to configure a region or regions of memory given a
+ * starting address and length to be readable by the host, or
+ * readable-writeable.
+ */
+#define ASPEED_P2A_CTRL_IOCTL_SET_WINDOW _IOW(__ASPEED_P2A_CTRL_IOCTL_MAGIC, \
+		0x00, struct aspeed_p2a_ctrl_mapping)
+
+/*
+ * This IOCTL is meant to read back to the user the base address and length of
+ * the memory-region specified to the driver for use with mmap.
+ */
+#define ASPEED_P2A_CTRL_IOCTL_GET_MEMORY_CONFIG \
+	_IOWR(__ASPEED_P2A_CTRL_IOCTL_MAGIC, \
+		0x01, struct aspeed_p2a_ctrl_mapping)
+
+#endif /* _UAPI_LINUX_ASPEED_P2A_CTRL_H */
-- 
2.21.0.392.gf8f6787159e-goog