Re: [PATCH v7 4/4] bus: mhi: Add userspace client interface driver

From: Hemant Kumar
Date: Wed Oct 21 2020 - 13:43:36 EST

Hi Mani,

On 10/21/20 9:11 AM, Manivannan Sadhasivam wrote:
On Fri, Oct 16, 2020 at 09:04:17PM -0700, Hemant Kumar wrote:
This MHI client driver allows userspace clients to transfer
raw data between MHI device and host using standard file operations.
Driver instantiates uci device object which is associated to device
file node. uci device object instantiates uci channel object when device
file node is opened. uci channel object is used to manage MHI channels
by calling MHI core APIs for read and write operations. MHI channels
are started as part of device open(). MHI channels remain in start
state until last release() is called on uci device file node. Device
file node is created with format

/dev/mhi_<controller_name>_<mhi_device_name>

Currently it supports LOOPBACK channel.

Signed-off-by: Hemant Kumar <hemantk@xxxxxxxxxxxxxx>
---
drivers/bus/mhi/Kconfig | 13 +
drivers/bus/mhi/Makefile | 4 +
drivers/bus/mhi/uci.c | 656 +++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 673 insertions(+)
create mode 100644 drivers/bus/mhi/uci.c

diff --git a/drivers/bus/mhi/Kconfig b/drivers/bus/mhi/Kconfig
index e841c10..3891b31 100644
--- a/drivers/bus/mhi/Kconfig
+++ b/drivers/bus/mhi/Kconfig
@@ -20,3 +20,16 @@ config MHI_BUS_DEBUG
Enable debugfs support for use with the MHI transport. Allows
reading and/or modifying some values within the MHI controller
for debug and test purposes.
+
+config MHI_UCI
+ tristate "MHI UCI"
+ depends on MHI_BUS
+ help
+ MHI based userspace client interface driver is used for transferring

Userspace Client Interface (UCI)
Done.

And please use the caps form UCI in comments throughout the driver.
Done. In commit text : "uci device object", "uci channel object" and "uci device file node" shall we change these as well ?

+ raw data between host and device using standard file operations from
+ userspace. Open, read, write, and close operations are supported
+ by this driver. Please check mhi_uci_match_table for all supported
+ channels that are exposed to userspace.
+
+ To compile this driver as a module, choose M here: the module will be
+ called mhi_uci.
diff --git a/drivers/bus/mhi/Makefile b/drivers/bus/mhi/Makefile
index 19e6443..80feefb 100644
--- a/drivers/bus/mhi/Makefile
+++ b/drivers/bus/mhi/Makefile
@@ -1,2 +1,6 @@
# core layer
obj-y += core/
+
+# MHI client
+mhi_uci-y := uci.o
+obj-$(CONFIG_MHI_UCI) += mhi_uci.o
diff --git a/drivers/bus/mhi/uci.c b/drivers/bus/mhi/uci.c
new file mode 100644
index 0000000..8334836
--- /dev/null
+++ b/drivers/bus/mhi/uci.c
@@ -0,0 +1,656 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2018-2020, The Linux Foundation. All rights reserved.*/
+
+#include <linux/kernel.h>
+#include <linux/mhi.h>
+#include <linux/mod_devicetable.h>
+#include <linux/module.h>
+#include <linux/poll.h>
+
+#define DEVICE_NAME "mhi"
+#define MHI_UCI_DRIVER_NAME "mhi_uci"
+#define MAX_UCI_MINORS (128)

No need of ().
Done.

+
+static DEFINE_IDR(uci_idr);
+static DEFINE_MUTEX(uci_drv_mutex);
+static struct class *uci_dev_class;
+static int uci_dev_major;
+
+/**
+ * struct uci_chan - MHI channel for a uci device
+ * @udev: associated uci device object
+ * @ul_wq: wait queue for writer
+ * @write_lock: mutex write lock for ul channel
+ * @dl_wq: wait queue for reader
+ * @read_lock: mutex read lock for dl channel
+ * @dl_lock: spin lock
+ * @pending: list of dl buffers userspace is waiting to read
+ * @cur_buf: current buffer userspace is reading
+ * @dl_size: size of the current dl buffer userspace is reading
+ * @ref_count: uci_chan reference count
+ */
+struct uci_chan {
+ struct uci_dev *udev;
+ wait_queue_head_t ul_wq;
+
+ /* ul channel lock to synchronize multiple writes */

Please move these inline comments to Kdoc.
This was added because checkpatch --strict required to add a comment when lock is added to struct, after adding inline comment, checkpatch
error was gone.

+ struct mutex write_lock;
+
+ wait_queue_head_t dl_wq;
+
+ /* dl channel lock to synchronize multiple reads */
+ struct mutex read_lock;
+
+ /*
+ * protects pending and cur_buf members in bh context, channel release,
+ * read and poll
+ */
+ spinlock_t dl_lock;
+
+ struct list_head pending;
+ struct uci_buf *cur_buf;
+ size_t dl_size;
+ struct kref ref_count;
+};
+
+/**
+ * struct uci_buf - uci buffer
+ * @data: data buffer
+ * @len: length of data buffer
+ * @node: list node of the uci buffer
+ */
+struct uci_buf {
+ void *data;
+ size_t len;
+ struct list_head node;
+};
+
+/**
+ * struct uci_dev - MHI uci device
+ * @minor: uci device node minor number
+ * @mhi_dev: associated mhi device object
+ * @uchan: uci uplink and downlink channel object
+ * @mtu: max TRE buffer length
+ * @enabled: uci device probed

Use something like, "Flag to track the state of the UCI device".
Done

+ * @lock: mutex lock to manage uchan object
+ * @ref_count: uci_dev reference count
+ */
+struct uci_dev {
+ unsigned int minor;
+ struct mhi_device *mhi_dev;
+ struct uci_chan *uchan;
+ size_t mtu;
+ bool enabled;
+
+ /* synchronize open, release and driver remove */
+ struct mutex lock;
+ struct kref ref_count;
+};
+

[...]

+
+static int mhi_uci_dev_start_chan(struct uci_dev *udev)
+{
+ int ret = 0;
+ struct uci_chan *uchan;
+
+ mutex_lock(&udev->lock);
+ if (!udev->uchan || !kref_get_unless_zero(&udev->uchan->ref_count)) {
+ uchan = kzalloc(sizeof(*uchan), GFP_KERNEL);
+ if (!uchan) {
+ ret = -ENOMEM;
+ goto error_chan_start;
+ }
+
+ udev->uchan = uchan;
+ uchan->udev = udev;
+ init_waitqueue_head(&uchan->ul_wq);
+ init_waitqueue_head(&uchan->dl_wq);
+ mutex_init(&uchan->write_lock);
+ mutex_init(&uchan->read_lock);
+ spin_lock_init(&uchan->dl_lock);
+ INIT_LIST_HEAD(&uchan->pending);
+
+ ret = mhi_prepare_for_transfer(udev->mhi_dev);
+ if (ret) {
+ dev_err(&udev->mhi_dev->dev, "Error starting transfer channels\n");
+ goto error_chan_cleanup;
+ }
+
+ ret = mhi_queue_inbound(udev);
+ if (ret)
+ goto error_chan_cleanup;
+
+ kref_init(&uchan->ref_count);
+ }
+
+ mutex_unlock(&udev->lock);

Please leave a new line before return.
Done.

+ return 0;
+
+error_chan_cleanup:
+ mhi_uci_dev_chan_release(&uchan->ref_count);
+error_chan_start:
+ mutex_unlock(&udev->lock);
+ return ret;
+}
+

[...]

+
+static int mhi_uci_probe(struct mhi_device *mhi_dev,
+ const struct mhi_device_id *id)
+{
+ struct uci_dev *udev;
+ struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
+ struct device *dev;
+ int index;
+
+ udev = kzalloc(sizeof(*udev), GFP_KERNEL);
+ if (!udev)
+ return -ENOMEM;
+
+ kref_init(&udev->ref_count);
+ mutex_init(&udev->lock);
+ udev->mhi_dev = mhi_dev;
+
+ mutex_lock(&uci_drv_mutex);

Do we really need the lock here?
Added this based on the comment from idr_alloc API
* The caller should provide their own locking to ensure that two
* concurrent modifications to the IDR are not possible.

+ index = idr_alloc(&uci_idr, udev, 0, MAX_UCI_MINORS, GFP_KERNEL);
+ mutex_unlock(&uci_drv_mutex);
+ if (index < 0) {
+ kfree(udev);
+ return index;
+ }
+
+ udev->minor = index;
+
+ udev->mtu = min_t(size_t, id->driver_data, MHI_MAX_MTU);
+ dev_set_drvdata(&mhi_dev->dev, udev);
+ udev->enabled = true;
+
+ /* create device file node /dev/mhi_<cntrl_dev_name>_<mhi_dev_name> */
+ dev = device_create(uci_dev_class, &mhi_dev->dev,
+ MKDEV(uci_dev_major, index), udev,
+ DEVICE_NAME "_%s_%s",
+ dev_name(mhi_cntrl->cntrl_dev), mhi_dev->name);
+ if (IS_ERR(dev)) {
+ mutex_lock(&uci_drv_mutex);
+ idr_remove(&uci_idr, udev->minor);
+ mutex_unlock(&uci_drv_mutex);
+ dev_set_drvdata(&mhi_dev->dev, NULL);
+ kfree(udev);
+ return PTR_ERR(dev);
+ }
+
+ dev_dbg(&mhi_dev->dev, "probed uci dev: minor %d\n", index);
+
+ return 0;
+};
+
+static void mhi_uci_remove(struct mhi_device *mhi_dev)
+{
+ struct uci_dev *udev = dev_get_drvdata(&mhi_dev->dev);
+
+ /* disable the node */
+ mutex_lock(&udev->lock);
+ udev->enabled = false;
+
+ /* delete the node to prevent new opens */
+ device_destroy(uci_dev_class, MKDEV(uci_dev_major, udev->minor));
+
+ /* return error for any blocked read or write */
+ if (udev->uchan) {
+ wake_up(&udev->uchan->ul_wq);
+ wake_up(&udev->uchan->dl_wq);
+ }
+ mutex_unlock(&udev->lock);
+
+ mutex_lock(&uci_drv_mutex);
+ idr_remove(&uci_idr, udev->minor);
+ kref_put(&udev->ref_count, mhi_uci_dev_release);
+ mutex_unlock(&uci_drv_mutex);
+}
+
+/* .driver_data stores max mtu */
+static const struct mhi_device_id mhi_uci_match_table[] = {
+ { .chan = "LOOPBACK", .driver_data = 0x1000},
+ {},
+};
+MODULE_DEVICE_TABLE(mhi, mhi_uci_match_table);
+
+static struct mhi_driver mhi_uci_driver = {
+ .id_table = mhi_uci_match_table,
+ .remove = mhi_uci_remove,
+ .probe = mhi_uci_probe,
+ .ul_xfer_cb = mhi_ul_xfer_cb,
+ .dl_xfer_cb = mhi_dl_xfer_cb,
+ .driver = {
+ .name = MHI_UCI_DRIVER_NAME,
+ },
+};
+
+static int mhi_uci_init(void)
+{
+ int ret;
+
+ ret = register_chrdev(0, MHI_UCI_DRIVER_NAME, &mhidev_fops);
+ if (ret < 0)
+ return ret;
+
+ uci_dev_major = ret;
+ uci_dev_class = class_create(THIS_MODULE, MHI_UCI_DRIVER_NAME);
+ if (IS_ERR(uci_dev_class)) {
+ unregister_chrdev(uci_dev_major, MHI_UCI_DRIVER_NAME);

Use an error path for cleaning this.
Done.

Thanks,
Mani

Thanks,
Hemant
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