[PATCH v18 0/3] userspace MHI client interface driver

[PATCH v18 0/3] userspace MHI client interface driver

[Hemant Kumar]

This patch series adds support for UCI driver. UCI driver enables userspace
clients to communicate to external MHI devices like modem. UCI driver probe
creates standard character device file nodes for userspace clients to
perform open, read, write, poll and release file operations. These file
operations call MHI core layer APIs to perform data transfer using MHI bus
to communicate with MHI device. 

This interface allows exposing modem control channel(s) such as QMI, MBIM,
or AT commands to userspace which can be used to configure the modem using
tools such as libqmi, ModemManager, minicom (for AT), etc over MHI. This is
required as there are no kernel APIs to access modem control path for device
configuration. Data path transporting the network payload (IP), however, is
routed to the Linux network via the mhi-net driver. Currently driver supports
QMI channel. libqmi is userspace MHI client which communicates to a QMI
service using QMI channel. Please refer to
https://www.freedesktop.org/wiki/Software/libqmi/ for additional information
on libqmi.

Patch is tested using arm64 and x86 based platform.

V18:
- Updated commit text for UCI to clarify why this driver is required for QMI
  over MHI. Also updated cover letter with same information.

v17:
- Updated commit text for UCI driver by mentioning about libqmi open-source
  userspace program that will be talking to this UCI kernel driver.
- UCI driver depends upon patch "bus: mhi: core: Add helper API to return number
  of free TREs".

v16:
- Removed reference of WLAN as an external MHI device in documentation and
  cover letter.

v15:
- Updated documentation related to poll and release operations.

V14:
- Fixed device file node format to /dev/<mhi_dev_name> instead of
  /dev/mhi_<mhi_dev_name> because "mhi" is already part of mhi device name.
  For example old format: /dev/mhi_mhi0_QMI new format: /dev/mhi0_QMI.
- Updated MHI documentation to reflect index mhi controller name in
  QMI usage example.

V13:
- Removed LOOPBACK channel from mhi_device_id table from this patch series.
  Pushing a new patch series to add support for LOOPBACK channel and the user
  space test application. Also removed the description from kernel documentation.
- Added QMI channel to mhi_device_id table. QMI channel has existing libqmi
  support from user space.
- Updated kernel Documentation for QMI channel and provided external reference
  for libqmi.
- Updated device file node name by appending mhi device name only, which already
  includes mhi controller device name.

V12:
- Added loopback test driver under selftest/drivers/mhi. Updated kernel
  documentation for the usage of the loopback test application.
- Addressed review comments for renaming variable names, updated inline
  comments and removed two redundant dev_dbg.

V11:
- Fixed review comments for UCI documentation by expanding TLAs and rewording
  some sentences.

V10:
- Replaced mutex_lock with mutex_lock_interruptible in read() and write() file
  ops call back.

V9:
- Renamed dl_lock to dl_pending _lock and pending list to dl_pending for
  clarity.
- Used read lock to protect cur_buf.
- Change transfer status check logic and only consider 0 and -EOVERFLOW as
  only success.
- Added __int to module init function.
- Print channel name instead of minor number upon successful probe.

V8:
- Fixed kernel test robot compilation error by changing %lu to %zu for
  size_t.
- Replaced uci with UCI in Kconfig, commit text, and comments in driver
  code.
- Fixed minor style related comments.

V7:
- Decoupled uci device and uci channel objects. uci device is
  associated with device file node. uci channel is associated
  with MHI channels. uci device refers to uci channel to perform
  MHI channel operations for device file operations like read()
  and write(). uci device increments its reference count for
  every open(). uci device calls mhi_uci_dev_start_chan() to start
  the MHI channel. uci channel object is tracking number of times
  MHI channel is referred. This allows to keep the MHI channel in
  start state until last release() is called. After that uci channel
  reference count goes to 0 and uci channel clean up is performed
  which stops the MHI channel. After the last call to release() if
  driver is removed uci reference count becomes 0 and uci object is
  cleaned up.
- Use separate uci channel read and write lock to fine grain locking
  between reader and writer.
- Use uci device lock to synchronize open, release and driver remove.
- Optimize for downlink only or uplink only UCI device.

V6:
- Moved uci.c to mhi directory.
- Updated Kconfig to add module information.
- Updated Makefile to rename uci object file name as mhi_uci
- Removed kref for open count

V5:
- Removed mhi_uci_drv structure.
- Used idr instead of creating global list of uci devices.
- Used kref instead of local ref counting for uci device and
  open count.
- Removed unlikely macro.

V4:
- Fix locking to protect proper struct members.
- Updated documentation describing uci client driver use cases.
- Fixed uci ref counting in mhi_uci_open for error case.
- Addressed style related review comments.

V3: Added documentation for MHI UCI driver.

V2:
- Added mutex lock to prevent multiple readers to access same
- mhi buffer which can result into use after free.



Hemant Kumar (3):
  bus: mhi: core: Move MHI_MAX_MTU to external header file
  docs: Add documentation for userspace client interface
  bus: mhi: Add userspace client interface driver

 Documentation/mhi/index.rst     |   1 +
 Documentation/mhi/uci.rst       |  95 ++++++
 drivers/bus/mhi/Kconfig         |  13 +
 drivers/bus/mhi/Makefile        |   3 +
 drivers/bus/mhi/core/internal.h |   1 -
 drivers/bus/mhi/uci.c           | 664 ++++++++++++++++++++++++++++++++++++++++
 include/linux/mhi.h             |   3 +
 7 files changed, 779 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/mhi/uci.rst
 create mode 100644 drivers/bus/mhi/uci.c

-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

[PATCH v18 1/3] bus: mhi: core: Move MHI_MAX_MTU to external header file

[Hemant Kumar]

Currently this macro is defined in internal MHI header as
a TRE length mask. Moving it to external header allows MHI
client drivers to set this upper bound for the transmit
buffer size.

Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
---
 drivers/bus/mhi/core/internal.h | 1 -
 include/linux/mhi.h             | 3 +++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/bus/mhi/core/internal.h b/drivers/bus/mhi/core/internal.h
index 6f80ec3..2b9c063 100644
--- a/drivers/bus/mhi/core/internal.h
+++ b/drivers/bus/mhi/core/internal.h
@@ -453,7 +453,6 @@ enum mhi_pm_state {
 #define CMD_EL_PER_RING			128
 #define PRIMARY_CMD_RING		0
 #define MHI_DEV_WAKE_DB			127
-#define MHI_MAX_MTU			0xffff
 #define MHI_RANDOM_U32_NONZERO(bmsk)	(prandom_u32_max(bmsk) + 1)
 
 enum mhi_er_type {
diff --git a/include/linux/mhi.h b/include/linux/mhi.h
index e36d575..f072605 100644
--- a/include/linux/mhi.h
+++ b/include/linux/mhi.h
@@ -15,6 +15,9 @@
 #include <linux/wait.h>
 #include <linux/workqueue.h>
 
+/* MHI client drivers to set this upper bound for tx buffer */
+#define MHI_MAX_MTU 0xffff
+
 #define MHI_MAX_OEM_PK_HASH_SEGMENTS 16
 
 struct mhi_chan;
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

[PATCH v18 2/3] docs: Add documentation for userspace client interface

[Hemant Kumar]

MHI userspace client driver is creating device file node
for user application to perform file operations. File
operations are handled by MHI core driver. Currently
QMI MHI channel is supported by this driver.

Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
---
 Documentation/mhi/index.rst |  1 +
 Documentation/mhi/uci.rst   | 95 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 Documentation/mhi/uci.rst

diff --git a/Documentation/mhi/index.rst b/Documentation/mhi/index.rst
index 1d8dec3..c75a371 100644
--- a/Documentation/mhi/index.rst
+++ b/Documentation/mhi/index.rst
@@ -9,6 +9,7 @@ MHI
 
    mhi
    topology
+   uci
 
 .. only::  subproject and html
 
diff --git a/Documentation/mhi/uci.rst b/Documentation/mhi/uci.rst
new file mode 100644
index 0000000..1e0a015
--- /dev/null
+++ b/Documentation/mhi/uci.rst
@@ -0,0 +1,95 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================
+Userspace Client Interface (UCI)
+=================================
+
+UCI driver enables userspace clients to communicate to external MHI devices
+like modem. UCI driver probe creates standard character device file nodes for
+userspace clients to perform open, read, write, poll and release file
+operations. UCI device object represents UCI device file node which gets
+instantiated as part of MHI UCI driver probe. UCI channel object represents
+MHI uplink or downlink channel.
+
+Operations
+==========
+
+open
+----
+
+Instantiates UCI channel object and starts MHI channels to move it to running
+state. Inbound buffers are queued to downlink channel transfer ring. Every
+subsequent open() increments UCI device reference count as well as UCI channel
+reference count.
+
+read
+----
+
+When data transfer is completed on downlink channel, transfer ring element
+buffer is copied to pending list. Reader is unblocked and data is copied to
+userspace buffer. Transfer ring element buffer is queued back to downlink
+channel transfer ring.
+
+write
+-----
+
+Write buffer is queued to uplink channel transfer ring if ring is not full. Upon
+uplink transfer completion buffer is freed.
+
+poll
+----
+
+Returns EPOLLIN | EPOLLRDNORM mask if pending list has buffers to be read by
+userspace. Returns EPOLLOUT | EPOLLWRNORM mask if MHI uplink channel transfer
+ring is not empty.  When the uplink channel transfer ring is non-empty, more
+data may be sent to the device. Returns EPOLLERR when UCI driver is removed.
+
+release
+-------
+
+Decrements UCI device reference count and UCI channel reference count. Upon
+last release() UCI channel clean up is performed. MHI channel moves to disable
+state and inbound buffers are freed.
+
+Usage
+=====
+
+Device file node is created with format:-
+
+/dev/<mhi_device_name>
+
+mhi_device_name includes mhi controller name and the name of the MHI channel
+being used by MHI client in userspace to send or receive data using MHI
+protocol.
+
+There is a separate character device file node created for each channel
+specified in MHI device id table. MHI channels are statically defined by MHI
+specification. The list of supported channels is in the channel list variable
+of mhi_device_id table in UCI driver.
+
+Qualcomm MSM Interface(QMI) Channel
+-----------------------------------
+
+Qualcomm MSM Interface(QMI) is a modem control messaging protocol used to
+communicate between software components in the modem and other peripheral
+subsystems. QMI communication is of request/response type or an unsolicited
+event type. libqmi is userspace MHI client which communicates to a QMI service
+using UCI device. It sends a QMI request to a QMI service using MHI channel 14
+or 16. QMI response is received using MHI channel 15 or 17 respectively. libqmi
+is a glib-based library for talking to WWAN modems and devices which speaks QMI
+protocol. For more information about libqmi please refer
+https://www.freedesktop.org/wiki/Software/libqmi/
+
+Usage Example
+~~~~~~~~~~~~~
+
+QMI command to retrieve device mode
+$ sudo qmicli -d /dev/mhi0_QMI --dms-get-model
+[/dev/mhi0_QMI] Device model retrieved:
+    Model: 'FN980m'
+
+Other Use Cases
+---------------
+
+Getting MHI device specific diagnostics information to userspace MHI diagnostic
+client using DIAG channel 4 (Host to device) and 5 (Device to Host).
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

[PATCH v18 3/3] bus: mhi: Add userspace client interface driver

[Hemant Kumar]

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_device_name>

This interface allows exposing modem control channel(s) such as QMI, MBIM,
or AT commands to userspace which can be used to configure the modem using
tools such as libqmi, ModemManager, minicom (for AT), etc over MHI. This is
required as there are no kernel APIs to access modem control path for device
configuration. Data path transporting the network payload (IP), however, is
routed to the Linux network via the mhi-net driver. Currently driver supports
QMI channel. libqmi is userspace MHI client which communicates to a QMI
service using QMI channel. Please refer to
https://www.freedesktop.org/wiki/Software/libqmi/ for additional information
on libqmi.

Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Jeffrey Hugo <jhugo@codeaurora.org>
Tested-by: Loic Poulain <loic.poulain@linaro.org>
---
 drivers/bus/mhi/Kconfig  |  13 +
 drivers/bus/mhi/Makefile |   3 +
 drivers/bus/mhi/uci.c    | 664 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 680 insertions(+)
 create mode 100644 drivers/bus/mhi/uci.c

diff --git a/drivers/bus/mhi/Kconfig b/drivers/bus/mhi/Kconfig
index da5cd0c..5194e8e 100644
--- a/drivers/bus/mhi/Kconfig
+++ b/drivers/bus/mhi/Kconfig
@@ -29,3 +29,16 @@ config MHI_BUS_PCI_GENERIC
 	  This driver provides MHI PCI controller driver for devices such as
 	  Qualcomm SDX55 based PCIe modems.
 
+config MHI_UCI
+	tristate "MHI UCI"
+	depends on MHI_BUS
+	help
+	  MHI based Userspace Client Interface (UCI) driver is used for
+	  transferring raw data between host and device using standard file
+	  operations from userspace. Open, read, write, poll 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 0a2d778..69f2111 100644
--- a/drivers/bus/mhi/Makefile
+++ b/drivers/bus/mhi/Makefile
@@ -4,3 +4,6 @@ obj-y += core/
 obj-$(CONFIG_MHI_BUS_PCI_GENERIC) += mhi_pci_generic.o
 mhi_pci_generic-y += pci_generic.o
 
+# 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..1df2377
--- /dev/null
+++ b/drivers/bus/mhi/uci.c
@@ -0,0 +1,664 @@
+// 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 MHI_UCI_DRIVER_NAME "mhi_uci"
+#define MHI_MAX_UCI_MINORS 128
+
+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_pending_lock: spin lock for dl_pending list
+ * @dl_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 */
+	struct mutex write_lock;
+
+	wait_queue_head_t dl_wq;
+
+	/* dl channel lock to synchronize multiple reads */
+	struct mutex read_lock;
+
+	/*
+	 * protects pending list in bh context, channel release, read and
+	 * poll
+	 */
+	spinlock_t dl_pending_lock;
+
+	struct list_head dl_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: Flag to track the state of the UCI device
+ * @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 void mhi_uci_dev_chan_release(struct kref *ref)
+{
+	struct uci_buf *buf_itr, *tmp;
+	struct uci_chan *uchan =
+		container_of(ref, struct uci_chan, ref_count);
+
+	if (uchan->udev->enabled)
+		mhi_unprepare_from_transfer(uchan->udev->mhi_dev);
+
+	spin_lock_bh(&uchan->dl_pending_lock);
+	list_for_each_entry_safe(buf_itr, tmp, &uchan->dl_pending, node) {
+		list_del(&buf_itr->node);
+		kfree(buf_itr->data);
+	}
+	spin_unlock_bh(&uchan->dl_pending_lock);
+
+	wake_up(&uchan->ul_wq);
+	wake_up(&uchan->dl_wq);
+
+	mutex_lock(&uchan->read_lock);
+	if (uchan->cur_buf)
+		kfree(uchan->cur_buf->data);
+
+	uchan->cur_buf = NULL;
+	mutex_unlock(&uchan->read_lock);
+
+	mutex_destroy(&uchan->write_lock);
+	mutex_destroy(&uchan->read_lock);
+
+	uchan->udev->uchan = NULL;
+	kfree(uchan);
+}
+
+static int mhi_queue_inbound(struct uci_dev *udev)
+{
+	struct mhi_device *mhi_dev = udev->mhi_dev;
+	struct device *dev = &mhi_dev->dev;
+	int nr_desc, i, ret = -EIO;
+	size_t dl_buf_size;
+	void *buf;
+	struct uci_buf *ubuf;
+
+	/*
+	 * skip queuing without error if dl channel is not supported. This
+	 * allows open to succeed for udev, supporting ul only channel.
+	 */
+	if (!udev->mhi_dev->dl_chan)
+		return 0;
+
+	nr_desc = mhi_get_free_desc_count(mhi_dev, DMA_FROM_DEVICE);
+
+	for (i = 0; i < nr_desc; i++) {
+		buf = kmalloc(udev->mtu, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
+
+		dl_buf_size = udev->mtu - sizeof(*ubuf);
+
+		/* save uci_buf info at the end of buf */
+		ubuf = buf + dl_buf_size;
+		ubuf->data = buf;
+
+		dev_dbg(dev, "Allocated buf %d of %d size %zu\n", i, nr_desc,
+			dl_buf_size);
+
+		ret = mhi_queue_buf(mhi_dev, DMA_FROM_DEVICE, buf, dl_buf_size,
+				    MHI_EOT);
+		if (ret) {
+			kfree(buf);
+			dev_err(dev, "Failed to queue buffer %d\n", i);
+			return ret;
+		}
+	}
+
+	return ret;
+}
+
+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_pending_lock);
+		INIT_LIST_HEAD(&uchan->dl_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);
+
+	return 0;
+
+error_chan_cleanup:
+	mhi_uci_dev_chan_release(&uchan->ref_count);
+error_chan_start:
+	mutex_unlock(&udev->lock);
+	return ret;
+}
+
+static void mhi_uci_dev_release(struct kref *ref)
+{
+	struct uci_dev *udev =
+		container_of(ref, struct uci_dev, ref_count);
+
+	mutex_destroy(&udev->lock);
+
+	kfree(udev);
+}
+
+static int mhi_uci_open(struct inode *inode, struct file *filp)
+{
+	unsigned int minor = iminor(inode);
+	struct uci_dev *udev = NULL;
+	int ret;
+
+	mutex_lock(&uci_drv_mutex);
+	udev = idr_find(&uci_idr, minor);
+	if (!udev) {
+		pr_debug("uci dev: minor %d not found\n", minor);
+		mutex_unlock(&uci_drv_mutex);
+		return -ENODEV;
+	}
+
+	kref_get(&udev->ref_count);
+	mutex_unlock(&uci_drv_mutex);
+
+	ret = mhi_uci_dev_start_chan(udev);
+	if (ret) {
+		kref_put(&udev->ref_count, mhi_uci_dev_release);
+		return ret;
+	}
+
+	filp->private_data = udev;
+
+	return 0;
+}
+
+static int mhi_uci_release(struct inode *inode, struct file *file)
+{
+	struct uci_dev *udev = file->private_data;
+
+	mutex_lock(&udev->lock);
+	kref_put(&udev->uchan->ref_count, mhi_uci_dev_chan_release);
+	mutex_unlock(&udev->lock);
+
+	kref_put(&udev->ref_count, mhi_uci_dev_release);
+
+	return 0;
+}
+
+static __poll_t mhi_uci_poll(struct file *file, poll_table *wait)
+{
+	struct uci_dev *udev = file->private_data;
+	struct mhi_device *mhi_dev = udev->mhi_dev;
+	struct device *dev = &mhi_dev->dev;
+	struct uci_chan *uchan = udev->uchan;
+	__poll_t mask = 0;
+
+	poll_wait(file, &udev->uchan->ul_wq, wait);
+	poll_wait(file, &udev->uchan->dl_wq, wait);
+
+	if (!udev->enabled) {
+		mask = EPOLLERR;
+		goto done;
+	}
+
+	spin_lock_bh(&uchan->dl_pending_lock);
+	if (!list_empty(&uchan->dl_pending) || uchan->cur_buf)
+		mask |= EPOLLIN | EPOLLRDNORM;
+	spin_unlock_bh(&uchan->dl_pending_lock);
+
+	if (mhi_get_free_desc_count(mhi_dev, DMA_TO_DEVICE) > 0)
+		mask |= EPOLLOUT | EPOLLWRNORM;
+
+	dev_dbg(dev, "Client attempted to poll, returning mask 0x%x\n", mask);
+
+done:
+	return mask;
+}
+
+static ssize_t mhi_uci_write(struct file *file,
+			     const char __user *buf,
+			     size_t count,
+			     loff_t *offp)
+{
+	struct uci_dev *udev = file->private_data;
+	struct mhi_device *mhi_dev = udev->mhi_dev;
+	struct device *dev = &mhi_dev->dev;
+	struct uci_chan *uchan = udev->uchan;
+	size_t bytes_xfered = 0;
+	int ret, nr_desc = 0;
+
+	/* if ul channel is not supported return error */
+	if (!mhi_dev->ul_chan)
+		return -EOPNOTSUPP;
+
+	if (!buf || !count)
+		return -EINVAL;
+
+	dev_dbg(dev, "%s: to xfer: %zu bytes\n", __func__, count);
+
+	if (mutex_lock_interruptible(&uchan->write_lock))
+		return -EINTR;
+
+	while (count) {
+		size_t xfer_size;
+		void *kbuf;
+		enum mhi_flags flags;
+
+		/* wait for free descriptors */
+		ret = wait_event_interruptible(uchan->ul_wq,
+					       (!udev->enabled) ||
+				(nr_desc = mhi_get_free_desc_count(mhi_dev,
+					       DMA_TO_DEVICE)) > 0);
+
+		if (ret == -ERESTARTSYS) {
+			dev_dbg(dev, "Interrupted by a signal in %s, exiting\n",
+				__func__);
+			goto err_mtx_unlock;
+		}
+
+		if (!udev->enabled) {
+			ret = -ENODEV;
+			goto err_mtx_unlock;
+		}
+
+		xfer_size = min_t(size_t, count, udev->mtu);
+		kbuf = kmalloc(xfer_size, GFP_KERNEL);
+		if (!kbuf) {
+			ret = -ENOMEM;
+			goto err_mtx_unlock;
+		}
+
+		ret = copy_from_user(kbuf, buf, xfer_size);
+		if (ret) {
+			kfree(kbuf);
+			ret = -EFAULT;
+			goto err_mtx_unlock;
+		}
+
+		/* if ring is full after this force EOT */
+		if (nr_desc > 1 && (count - xfer_size))
+			flags = MHI_CHAIN;
+		else
+			flags = MHI_EOT;
+
+		ret = mhi_queue_buf(mhi_dev, DMA_TO_DEVICE, kbuf, xfer_size,
+				    flags);
+		if (ret) {
+			kfree(kbuf);
+			goto err_mtx_unlock;
+		}
+
+		bytes_xfered += xfer_size;
+		count -= xfer_size;
+		buf += xfer_size;
+	}
+
+	mutex_unlock(&uchan->write_lock);
+	dev_dbg(dev, "%s: bytes xferred: %zu\n", __func__, bytes_xfered);
+
+	return bytes_xfered;
+
+err_mtx_unlock:
+	mutex_unlock(&uchan->write_lock);
+
+	return ret;
+}
+
+static ssize_t mhi_uci_read(struct file *file,
+			    char __user *buf,
+			    size_t count,
+			    loff_t *ppos)
+{
+	struct uci_dev *udev = file->private_data;
+	struct mhi_device *mhi_dev = udev->mhi_dev;
+	struct uci_chan *uchan = udev->uchan;
+	struct device *dev = &mhi_dev->dev;
+	struct uci_buf *ubuf;
+	size_t rx_buf_size;
+	char *ptr;
+	size_t to_copy;
+	int ret = 0;
+
+	/* if dl channel is not supported return error */
+	if (!mhi_dev->dl_chan)
+		return -EOPNOTSUPP;
+
+	if (!buf)
+		return -EINVAL;
+
+	if (mutex_lock_interruptible(&uchan->read_lock))
+		return -EINTR;
+
+	spin_lock_bh(&uchan->dl_pending_lock);
+	/* No data available to read, wait */
+	if (!uchan->cur_buf && list_empty(&uchan->dl_pending)) {
+		dev_dbg(dev, "No data available to read, waiting\n");
+
+		spin_unlock_bh(&uchan->dl_pending_lock);
+		ret = wait_event_interruptible(uchan->dl_wq,
+					       (!udev->enabled ||
+					      !list_empty(&uchan->dl_pending)));
+
+		if (ret == -ERESTARTSYS) {
+			dev_dbg(dev, "Interrupted by a signal in %s, exiting\n",
+				__func__);
+			goto err_mtx_unlock;
+		}
+
+		if (!udev->enabled) {
+			ret = -ENODEV;
+			goto err_mtx_unlock;
+		}
+		spin_lock_bh(&uchan->dl_pending_lock);
+	}
+
+	/* new read, get the next descriptor from the list */
+	if (!uchan->cur_buf) {
+		ubuf = list_first_entry_or_null(&uchan->dl_pending,
+						struct uci_buf, node);
+		if (!ubuf) {
+			ret = -EIO;
+			goto err_spin_unlock;
+		}
+
+		list_del(&ubuf->node);
+		uchan->cur_buf = ubuf;
+		uchan->dl_size = ubuf->len;
+		dev_dbg(dev, "Got pkt of size: %zu\n", uchan->dl_size);
+	}
+	spin_unlock_bh(&uchan->dl_pending_lock);
+
+	ubuf = uchan->cur_buf;
+
+	/* Copy the buffer to user space */
+	to_copy = min_t(size_t, count, uchan->dl_size);
+	ptr = ubuf->data + (ubuf->len - uchan->dl_size);
+
+	ret = copy_to_user(buf, ptr, to_copy);
+	if (ret) {
+		ret = -EFAULT;
+		goto err_mtx_unlock;
+	}
+
+	dev_dbg(dev, "Copied %zu of %zu bytes\n", to_copy, uchan->dl_size);
+	uchan->dl_size -= to_copy;
+
+	/* we finished with this buffer, queue it back to hardware */
+	if (!uchan->dl_size) {
+		uchan->cur_buf = NULL;
+
+		rx_buf_size = udev->mtu - sizeof(*ubuf);
+		ret = mhi_queue_buf(mhi_dev, DMA_FROM_DEVICE, ubuf->data,
+				    rx_buf_size, MHI_EOT);
+		if (ret) {
+			dev_err(dev, "Failed to recycle element: %d\n", ret);
+			kfree(ubuf->data);
+			goto err_mtx_unlock;
+		}
+	}
+	mutex_unlock(&uchan->read_lock);
+
+	dev_dbg(dev, "%s: Returning %zu bytes\n", __func__, to_copy);
+
+	return to_copy;
+
+err_spin_unlock:
+	spin_unlock_bh(&uchan->dl_pending_lock);
+err_mtx_unlock:
+	mutex_unlock(&uchan->read_lock);
+	return ret;
+}
+
+static const struct file_operations mhidev_fops = {
+	.owner = THIS_MODULE,
+	.open = mhi_uci_open,
+	.release = mhi_uci_release,
+	.read = mhi_uci_read,
+	.write = mhi_uci_write,
+	.poll = mhi_uci_poll,
+};
+
+static void mhi_ul_xfer_cb(struct mhi_device *mhi_dev,
+			   struct mhi_result *mhi_result)
+{
+	struct uci_dev *udev = dev_get_drvdata(&mhi_dev->dev);
+	struct uci_chan *uchan = udev->uchan;
+	struct device *dev = &mhi_dev->dev;
+
+	dev_dbg(dev, "%s: status: %d xfer_len: %zu\n", __func__,
+		mhi_result->transaction_status, mhi_result->bytes_xferd);
+
+	kfree(mhi_result->buf_addr);
+
+	if (!mhi_result->transaction_status)
+		wake_up(&uchan->ul_wq);
+}
+
+static void mhi_dl_xfer_cb(struct mhi_device *mhi_dev,
+			   struct mhi_result *mhi_result)
+{
+	struct uci_dev *udev = dev_get_drvdata(&mhi_dev->dev);
+	struct uci_chan *uchan = udev->uchan;
+	struct device *dev = &mhi_dev->dev;
+	struct uci_buf *ubuf;
+	size_t dl_buf_size = udev->mtu - sizeof(*ubuf);
+
+	dev_dbg(dev, "%s: status: %d receive_len: %zu\n", __func__,
+		mhi_result->transaction_status, mhi_result->bytes_xferd);
+
+	if (mhi_result->transaction_status &&
+	    mhi_result->transaction_status != -EOVERFLOW) {
+		kfree(mhi_result->buf_addr);
+		return;
+	}
+
+	ubuf = mhi_result->buf_addr + dl_buf_size;
+	ubuf->data = mhi_result->buf_addr;
+	ubuf->len = mhi_result->bytes_xferd;
+	spin_lock_bh(&uchan->dl_pending_lock);
+	list_add_tail(&ubuf->node, &uchan->dl_pending);
+	spin_unlock_bh(&uchan->dl_pending_lock);
+
+	wake_up(&uchan->dl_wq);
+}
+
+static int mhi_uci_probe(struct mhi_device *mhi_dev,
+			 const struct mhi_device_id *id)
+{
+	struct uci_dev *udev;
+	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);
+	index = idr_alloc(&uci_idr, udev, 0, MHI_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_dev_name> */
+	dev = device_create(uci_dev_class, &mhi_dev->dev,
+			    MKDEV(uci_dev_major, index), udev, "%s",
+			    dev_name(&mhi_dev->dev));
+	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: %s\n", id->chan);
+
+	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 = "QMI", .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 __init 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);
+		return PTR_ERR(uci_dev_class);
+	}
+
+	ret = mhi_driver_register(&mhi_uci_driver);
+	if (ret) {
+		class_destroy(uci_dev_class);
+		unregister_chrdev(uci_dev_major, MHI_UCI_DRIVER_NAME);
+	}
+
+	return ret;
+}
+
+static void __exit mhi_uci_exit(void)
+{
+	mhi_driver_unregister(&mhi_uci_driver);
+	class_destroy(uci_dev_class);
+	unregister_chrdev(uci_dev_major, MHI_UCI_DRIVER_NAME);
+	idr_destroy(&uci_idr);
+}
+
+module_init(mhi_uci_init);
+module_exit(mhi_uci_exit);
+MODULE_LICENSE("GPL v2");
+MODULE_DESCRIPTION("MHI UCI Driver");
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH v18 0/3] userspace MHI client interface driver

[Loic Poulain]

Hi Folks,

On Fri, 11 Dec 2020 at 20:45, Hemant Kumar <hemantk@codeaurora.org> wrote:
>
> This patch series adds support for UCI driver. UCI driver enables userspace
> clients to communicate to external MHI devices like modem. UCI driver probe
> creates standard character device file nodes for userspace clients to
> perform open, read, write, poll and release file operations. These file
> operations call MHI core layer APIs to perform data transfer using MHI bus
> to communicate with MHI device.
>
> This interface allows exposing modem control channel(s) such as QMI, MBIM,
> or AT commands to userspace which can be used to configure the modem using
> tools such as libqmi, ModemManager, minicom (for AT), etc over MHI. This is
> required as there are no kernel APIs to access modem control path for device
> configuration. Data path transporting the network payload (IP), however, is
> routed to the Linux network via the mhi-net driver. Currently driver supports
> QMI channel. libqmi is userspace MHI client which communicates to a QMI
> service using QMI channel. Please refer to
> https://www.freedesktop.org/wiki/Software/libqmi/ for additional information
> on libqmi.
>
> Patch is tested using arm64 and x86 based platform.

Are there any blockers or unadressed comments remaining on this
series? As far as I understand, the original blocker was the net/WiFi
mention in the commit message, that caused a legitimate concern from
network maintainer. It has been clarified now that this driver is not
for exposing any channel that could be otherwise handled properly by
an existing Linux subsystem/interface. It will be especially used as a
pipe for modem QMI channel (or AT commands) in the same way as the USB
CDC-WDM driver is doing (keeping userspace compatibility). Other MHI
channels, such as network data, QRTR, etc are not exposed and
correctly bound to the corresponding Linux subsystems.

The correlated worry was that it could be a userspace channel facility
for 'everything qualcomm', but we could say the same for other
existing busses with userspace shunt (/dev/bus/usb, /dev/i2c,
/dev/spidev, PCI UIO, UART...). Moreover, it is mitigated by the fact
that not all MHI channels are exposed by default, but only the allowed
ones (QMI in the initial version). For sure, special care must be
given to any further channel addition.

Regards,
Loic

Re: [PATCH v18 0/3] userspace MHI client interface driver

[Greg Kroah-Hartman]

On Wed, Dec 16, 2020 at 10:17:30AM +0100, Loic Poulain wrote:
> Hi Folks,
> 
> On Fri, 11 Dec 2020 at 20:45, Hemant Kumar <hemantk@codeaurora.org> wrote:
> >
> > This patch series adds support for UCI driver. UCI driver enables userspace
> > clients to communicate to external MHI devices like modem. UCI driver probe
> > creates standard character device file nodes for userspace clients to
> > perform open, read, write, poll and release file operations. These file
> > operations call MHI core layer APIs to perform data transfer using MHI bus
> > to communicate with MHI device.
> >
> > This interface allows exposing modem control channel(s) such as QMI, MBIM,
> > or AT commands to userspace which can be used to configure the modem using
> > tools such as libqmi, ModemManager, minicom (for AT), etc over MHI. This is
> > required as there are no kernel APIs to access modem control path for device
> > configuration. Data path transporting the network payload (IP), however, is
> > routed to the Linux network via the mhi-net driver. Currently driver supports
> > QMI channel. libqmi is userspace MHI client which communicates to a QMI
> > service using QMI channel. Please refer to
> > https://www.freedesktop.org/wiki/Software/libqmi/ for additional information
> > on libqmi.
> >
> > Patch is tested using arm64 and x86 based platform.
> 
> Are there any blockers or unadressed comments remaining on this
> series? As far as I understand, the original blocker was the net/WiFi
> mention in the commit message, that caused a legitimate concern from
> network maintainer. It has been clarified now that this driver is not
> for exposing any channel that could be otherwise handled properly by
> an existing Linux subsystem/interface. It will be especially used as a
> pipe for modem QMI channel (or AT commands) in the same way as the USB
> CDC-WDM driver is doing (keeping userspace compatibility). Other MHI
> channels, such as network data, QRTR, etc are not exposed and
> correctly bound to the corresponding Linux subsystems.
> 
> The correlated worry was that it could be a userspace channel facility
> for 'everything qualcomm', but we could say the same for other
> existing busses with userspace shunt (/dev/bus/usb, /dev/i2c,
> /dev/spidev, PCI UIO, UART...). Moreover, it is mitigated by the fact
> that not all MHI channels are exposed by default, but only the allowed
> ones (QMI in the initial version). For sure, special care must be
> given to any further channel addition.

It's the middle of the merge window, we can't do anything with new
patches at all until 5.11-rc1 is out, so please be patient.

thanks,

greg k-h