[PATCH v5 0/4] user space client interface driver

[PATCH v5 0/4] user space client interface driver

[Hemant Kumar]

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 (4):
  bus: mhi: core: Add helper API to return number of free TREs
  bus: mhi: core: Move MHI_MAX_MTU to external header file
  docs: Add documentation for userspace client interface
  bus: mhi: clients: Add userspace client interface driver

 Documentation/mhi/index.rst      |   1 +
 Documentation/mhi/uci.rst        |  39 +++
 drivers/bus/mhi/Kconfig          |   6 +
 drivers/bus/mhi/Makefile         |   1 +
 drivers/bus/mhi/clients/Kconfig  |  15 +
 drivers/bus/mhi/clients/Makefile |   3 +
 drivers/bus/mhi/clients/uci.c    | 662 +++++++++++++++++++++++++++++++++++++++
 drivers/bus/mhi/core/internal.h  |   1 -
 drivers/bus/mhi/core/main.c      |  12 +
 include/linux/mhi.h              |  12 +
 10 files changed, 751 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/mhi/uci.rst
 create mode 100644 drivers/bus/mhi/clients/Kconfig
 create mode 100644 drivers/bus/mhi/clients/Makefile
 create mode 100644 drivers/bus/mhi/clients/uci.c

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

[PATCH v5 1/4] bus: mhi: core: Add helper API to return number of free TREs

[Hemant Kumar]

Introduce mhi_get_no_free_descriptors() API to return number
of TREs available to queue buffer. MHI clients can use this
API to know before hand if ring is full without calling queue
API.

Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
---
 drivers/bus/mhi/core/main.c | 12 ++++++++++++
 include/linux/mhi.h         |  9 +++++++++
 2 files changed, 21 insertions(+)

diff --git a/drivers/bus/mhi/core/main.c b/drivers/bus/mhi/core/main.c
index 2cff5dd..0599e7d 100644
--- a/drivers/bus/mhi/core/main.c
+++ b/drivers/bus/mhi/core/main.c
@@ -258,6 +258,18 @@ int mhi_destroy_device(struct device *dev, void *data)
 	return 0;
 }
 
+int mhi_get_no_free_descriptors(struct mhi_device *mhi_dev,
+				enum dma_data_direction dir)
+{
+	struct mhi_controller *mhi_cntrl = mhi_dev->mhi_cntrl;
+	struct mhi_chan *mhi_chan = (dir == DMA_TO_DEVICE) ?
+		mhi_dev->ul_chan : mhi_dev->dl_chan;
+	struct mhi_ring *tre_ring = &mhi_chan->tre_ring;
+
+	return get_nr_avail_ring_elements(mhi_cntrl, tre_ring);
+}
+EXPORT_SYMBOL_GPL(mhi_get_no_free_descriptors);
+
 void mhi_notify(struct mhi_device *mhi_dev, enum mhi_callback cb_reason)
 {
 	struct mhi_driver *mhi_drv;
diff --git a/include/linux/mhi.h b/include/linux/mhi.h
index a35d876..6565528 100644
--- a/include/linux/mhi.h
+++ b/include/linux/mhi.h
@@ -600,6 +600,15 @@ void mhi_set_mhi_state(struct mhi_controller *mhi_cntrl,
 void mhi_notify(struct mhi_device *mhi_dev, enum mhi_callback cb_reason);
 
 /**
+ * mhi_get_no_free_descriptors - Get transfer ring length
+ * Get # of TD available to queue buffers
+ * @mhi_dev: Device associated with the channels
+ * @dir: Direction of the channel
+ */
+int mhi_get_no_free_descriptors(struct mhi_device *mhi_dev,
+				enum dma_data_direction dir);
+
+/**
  * mhi_prepare_for_power_up - Do pre-initialization before power up.
  *                            This is optional, call this before power up if
  *                            the controller does not want bus framework to
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

[PATCH v5 2/4] 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>
---
 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 7989269..4abf0cf 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 6565528..610f3b0 100644
--- a/include/linux/mhi.h
+++ b/include/linux/mhi.h
@@ -16,6 +16,9 @@
 #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 v5 3/4] 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
Loopback MHI channel is supported by this driver.

Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
---
 Documentation/mhi/index.rst |  1 +
 Documentation/mhi/uci.rst   | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 40 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..5d92939
--- /dev/null
+++ b/Documentation/mhi/uci.rst
@@ -0,0 +1,39 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=================================
+Userspace Client Interface (UCI)
+=================================
+
+UCI driver enables userspace clients to communicate to external MHI devices
+like modem and WLAN. It creates standard character device file nodes for user
+space clients to perform open, read, write, poll and close file operations.
+
+Device file node is created with format:-
+
+/dev/mhi_<controller_name>_<mhi_device_name>
+
+controller_name is the name of underlying bus used to transfer data.
+mhi_device_name is 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.
+Driver currently supports LOOPBACK channel 0 (Host to device) and 1 (Device to Host).
+
+LOOPBACK Channel
+----------------
+
+Userspace MHI client using LOOPBACK channel opens device file node. As part of
+open operation TREs to transfer ring of LOOPBACK channel 1 gets queued and channel
+doorbell is rung. When userspace MHI client performs write operation on device node,
+data buffer gets queued as a TRE to transfer ring of LOOPBACK channel 0. MHI Core
+driver rings the channel doorbell for MHI device to move data over underlying bus.
+When userspace MHI client driver performs read operation, same data gets looped back
+to MHI host using LOOPBACK channel 1. LOOPBACK channel is used to verify data path
+and data integrity between MHI Host and MHI device.
+
+Other Use Cases
+---------------
+
+Getting MHI device specific diagnostics information to userspace MHI diag 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 v5 4/4] bus: mhi: clients: 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.
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@codeaurora.org>
---
 drivers/bus/mhi/Kconfig          |   6 +
 drivers/bus/mhi/Makefile         |   1 +
 drivers/bus/mhi/clients/Kconfig  |  15 +
 drivers/bus/mhi/clients/Makefile |   3 +
 drivers/bus/mhi/clients/uci.c    | 662 +++++++++++++++++++++++++++++++++++++++
 5 files changed, 687 insertions(+)
 create mode 100644 drivers/bus/mhi/clients/Kconfig
 create mode 100644 drivers/bus/mhi/clients/Makefile
 create mode 100644 drivers/bus/mhi/clients/uci.c

diff --git a/drivers/bus/mhi/Kconfig b/drivers/bus/mhi/Kconfig
index 6a217ff..927c392 100644
--- a/drivers/bus/mhi/Kconfig
+++ b/drivers/bus/mhi/Kconfig
@@ -20,3 +20,9 @@ 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.
+
+if MHI_BUS
+
+source "drivers/bus/mhi/clients/Kconfig"
+
+endif
diff --git a/drivers/bus/mhi/Makefile b/drivers/bus/mhi/Makefile
index 19e6443..48f6028 100644
--- a/drivers/bus/mhi/Makefile
+++ b/drivers/bus/mhi/Makefile
@@ -1,2 +1,3 @@
 # core layer
 obj-y += core/
+obj-y += clients/
diff --git a/drivers/bus/mhi/clients/Kconfig b/drivers/bus/mhi/clients/Kconfig
new file mode 100644
index 0000000..37aaf51
--- /dev/null
+++ b/drivers/bus/mhi/clients/Kconfig
@@ -0,0 +1,15 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+menu "MHI clients support"
+
+config MHI_UCI
+       tristate "MHI UCI"
+       depends on MHI_BUS
+       help
+	 MHI based userspace client interface driver is used for transferring
+	 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.
+
+endmenu
diff --git a/drivers/bus/mhi/clients/Makefile b/drivers/bus/mhi/clients/Makefile
new file mode 100644
index 0000000..cd34282
--- /dev/null
+++ b/drivers/bus/mhi/clients/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0-only
+
+obj-$(CONFIG_MHI_UCI) += uci.o
diff --git a/drivers/bus/mhi/clients/uci.c b/drivers/bus/mhi/clients/uci.c
new file mode 100644
index 0000000..a25d5d0
--- /dev/null
+++ b/drivers/bus/mhi/clients/uci.c
@@ -0,0 +1,662 @@
+// 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)
+
+static DEFINE_IDR(uci_idr);
+static DEFINE_MUTEX(uci_idr_mutex);
+static struct class *uci_dev_class;
+static int uci_dev_major = -1;
+
+/**
+ * struct uci_chan - MHI channel for a uci device
+ * @wq: wait queue for reader/writer
+ * @lock: spin lock
+ * @pending: list of rx buffers userspace is waiting to read
+ * @cur_buf: current buffer userspace is reading
+ * @rx_size: size of the current rx buffer userspace is reading
+ */
+struct uci_chan {
+	wait_queue_head_t wq;
+
+	/* protects pending and cur_buf members */
+	spinlock_t lock;
+
+	struct list_head pending;
+	struct uci_buf *cur_buf;
+	size_t rx_size;
+};
+
+/**
+ * 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
+ * @chan: MHI channel name
+ * @lock: mutex lock
+ * @ul_chan: uplink uci channel object
+ * @dl_chan: downlink uci channel object
+ * @mtu: max tx buffer length
+ * @actual_mtu: maximum size of incoming buffer
+ * @ref_count: uci_dev reference count
+ * @open_count: device node open count
+ * @enabled: uci device probed
+ */
+struct uci_dev {
+	unsigned int minor;
+	struct mhi_device *mhi_dev;
+	const char *chan;
+
+	/* protects uci_dev struct members */
+	struct mutex lock;
+
+	struct uci_chan ul_chan;
+	struct uci_chan dl_chan;
+	size_t mtu;
+	size_t actual_mtu;
+	struct kref ref_count;
+	struct kref open_count;
+	bool enabled;
+};
+
+static int mhi_queue_inbound(struct uci_dev *udev)
+{
+	struct mhi_device *mhi_dev = udev->mhi_dev;
+	struct device *dev = &mhi_dev->dev;
+	size_t mtu = udev->mtu;
+	size_t actual_mtu = udev->actual_mtu;
+	int nr_trbs, i, ret = -EIO;
+	void *buf;
+	struct uci_buf *uci_buf;
+
+	nr_trbs = mhi_get_no_free_descriptors(mhi_dev, DMA_FROM_DEVICE);
+
+	for (i = 0; i < nr_trbs; i++) {
+		buf = kmalloc(mtu, GFP_KERNEL);
+		if (!buf)
+			return -ENOMEM;
+
+		uci_buf = buf + actual_mtu;
+		uci_buf->data = buf;
+
+		dev_dbg(dev, "Allocated buf %d of %d size %ld\n", i, nr_trbs,
+			actual_mtu);
+
+		ret = mhi_queue_buf(mhi_dev, DMA_FROM_DEVICE, buf, actual_mtu,
+				    MHI_EOT);
+		if (ret) {
+			kfree(buf);
+			dev_err(dev, "Failed to queue buffer %d\n", i);
+			return ret;
+		}
+	}
+
+	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);
+
+	dev_set_drvdata(&udev->mhi_dev->dev, NULL);
+
+	kfree(udev);
+}
+
+static void mhi_uci_close(struct kref *ref)
+{
+	struct uci_dev *udev =
+		container_of(ref, struct uci_dev, open_count);
+	struct uci_buf *itr, *tmp;
+	struct uci_chan *uchan;
+
+	if (udev->enabled)
+		mhi_unprepare_from_transfer(udev->mhi_dev);
+
+	/* clean inbound channel */
+	uchan = &udev->dl_chan;
+
+	spin_lock_bh(&uchan->lock);
+	list_for_each_entry_safe(itr, tmp, &uchan->pending, node) {
+		list_del(&itr->node);
+		kfree(itr->data);
+	}
+
+	if (uchan->cur_buf)
+		kfree(uchan->cur_buf->data);
+
+	uchan->cur_buf = NULL;
+	spin_unlock_bh(&uchan->lock);
+}
+
+static int mhi_uci_release(struct inode *inode, struct file *file)
+{
+	struct uci_dev *udev = file->private_data;
+
+	kref_put(&udev->open_count, mhi_uci_close);
+	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;
+	__poll_t mask = 0;
+
+	poll_wait(file, &udev->dl_chan.wq, wait);
+	poll_wait(file, &udev->ul_chan.wq, wait);
+
+	if (!udev->enabled) {
+		mask = EPOLLERR;
+	} else {
+		uchan = &udev->dl_chan;
+		spin_lock_bh(&uchan->lock);
+		if (!list_empty(&uchan->pending) || uchan->cur_buf) {
+			dev_dbg(dev, "Client can read from node\n");
+			mask |= EPOLLIN | EPOLLRDNORM;
+		}
+		spin_unlock_bh(&uchan->lock);
+	}
+
+	if (!udev->enabled) {
+		mask |= EPOLLERR;
+	} else if (mhi_get_no_free_descriptors(mhi_dev, DMA_TO_DEVICE) > 0) {
+		dev_dbg(dev, "Client can write to node\n");
+		mask |= EPOLLOUT | EPOLLWRNORM;
+	}
+
+	dev_dbg(dev, "Client attempted to poll, returning mask 0x%x\n", mask);
+
+	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->ul_chan;
+	size_t bytes_xfered = 0;
+	int ret, nr_avail = 0;
+
+	if (!buf || !count)
+		return -EINVAL;
+
+	/* confirm channel is active */
+	mutex_lock(&udev->lock);
+	if (!udev->enabled) {
+		ret = -ENODEV;
+		goto err_mtx_unlock;
+	}
+
+	dev_dbg(dev, "%s: to xfer: %lu bytes\n", __func__, count);
+
+	while (count) {
+		size_t xfer_size;
+		void *kbuf;
+		enum mhi_flags flags;
+
+		mutex_unlock(&udev->lock);
+		/* wait for free descriptors */
+		ret = wait_event_interruptible(uchan->wq,
+					       (!udev->enabled) ||
+				(nr_avail = mhi_get_no_free_descriptors(mhi_dev,
+					       DMA_TO_DEVICE)) > 0);
+
+		mutex_lock(&udev->lock);
+		if (ret == -ERESTARTSYS) {
+			dev_dbg(dev, "Exit signal caught for node\n");
+			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_avail > 1 && (count - xfer_size))
+			flags = MHI_CHAIN;
+		else
+			flags = MHI_EOT;
+
+		if (udev->enabled)
+			ret = mhi_queue_buf(mhi_dev, DMA_TO_DEVICE, kbuf,
+					    xfer_size, flags);
+		else
+			ret = -ENODEV;
+
+		if (ret) {
+			kfree(kbuf);
+			goto err_mtx_unlock;
+		}
+
+		bytes_xfered += xfer_size;
+		count -= xfer_size;
+		buf += xfer_size;
+	}
+
+	mutex_unlock(&udev->lock);
+	dev_dbg(dev, "%s: bytes xferred: %lu\n", __func__, bytes_xfered);
+
+	return bytes_xfered;
+
+err_mtx_unlock:
+	mutex_unlock(&udev->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->dl_chan;
+	struct device *dev = &mhi_dev->dev;
+	struct uci_buf *ubuf;
+	char *ptr;
+	size_t to_copy;
+	int ret = 0;
+
+	if (!buf)
+		return -EINVAL;
+
+	mutex_lock(&udev->lock);
+	/* confirm channel is active */
+	if (!udev->enabled) {
+		ret = -ENODEV;
+		goto err_mtx_unlock;
+	}
+
+	spin_lock_bh(&uchan->lock);
+	/* No data available to read, wait */
+	if (!uchan->cur_buf && list_empty(&uchan->pending)) {
+		dev_dbg(dev, "No data available to read waiting\n");
+
+		spin_unlock_bh(&uchan->lock);
+		mutex_unlock(&udev->lock);
+		ret = wait_event_interruptible(uchan->wq,
+					       (!udev->enabled ||
+					      !list_empty(&uchan->pending)));
+
+		mutex_lock(&udev->lock);
+		if (ret == -ERESTARTSYS) {
+			dev_dbg(dev, "Exit signal caught for node\n");
+			goto err_mtx_unlock;
+		}
+
+		if (!udev->enabled) {
+			ret = -ENODEV;
+			goto err_mtx_unlock;
+		}
+		spin_lock_bh(&uchan->lock);
+	}
+
+	/* new read, get the next descriptor from the list */
+	if (!uchan->cur_buf) {
+		ubuf = list_first_entry_or_null(&uchan->pending,
+						struct uci_buf, node);
+		if (!ubuf) {
+			ret = -EIO;
+			goto err_spin_unlock;
+		}
+
+		list_del(&ubuf->node);
+		uchan->cur_buf = ubuf;
+		uchan->rx_size = ubuf->len;
+		dev_dbg(dev, "Got pkt of size: %zu\n", uchan->rx_size);
+	}
+
+	ubuf = uchan->cur_buf;
+
+	/* Copy the buffer to user space */
+	to_copy = min_t(size_t, count, uchan->rx_size);
+	ptr = ubuf->data + (ubuf->len - uchan->rx_size);
+	spin_unlock_bh(&uchan->lock);
+
+	ret = copy_to_user(buf, ptr, to_copy);
+	if (ret) {
+		ret = -EFAULT;
+		goto err_mtx_unlock;
+	}
+
+	spin_lock_bh(&uchan->lock);
+
+	dev_dbg(dev, "Copied %lu of %lu bytes\n", to_copy, uchan->rx_size);
+	uchan->rx_size -= to_copy;
+
+	/* we finished with this buffer, queue it back to hardware */
+	if (!uchan->rx_size) {
+		uchan->cur_buf = NULL;
+
+		if (udev->enabled)
+			ret = mhi_queue_buf(mhi_dev, DMA_FROM_DEVICE,
+					    ubuf->data,
+					    udev->actual_mtu, MHI_EOT);
+		else
+			ret = -ENODEV;
+
+		if (ret) {
+			dev_err(dev, "Failed to recycle element: %d\n", ret);
+			kfree(ubuf->data);
+			goto err_spin_unlock;
+		}
+	}
+	spin_unlock_bh(&uchan->lock);
+	mutex_unlock(&udev->lock);
+
+	dev_dbg(dev, "%s: Returning %lu bytes\n", __func__, to_copy);
+
+	return to_copy;
+
+err_spin_unlock:
+	spin_unlock_bh(&uchan->lock);
+err_mtx_unlock:
+	mutex_unlock(&udev->lock);
+	return ret;
+}
+
+static int mhi_uci_open(struct inode *inode, struct file *filp)
+{
+	struct uci_dev *udev = NULL;
+	unsigned int minor = iminor(inode);
+	int ret = -EIO;
+	struct uci_buf *buf_itr, *tmp;
+	struct uci_chan *dl_chan;
+	struct mhi_device *mhi_dev;
+	struct device *dev;
+
+	mutex_lock(&uci_idr_mutex);
+	udev = idr_find(&uci_idr, minor);
+	mutex_unlock(&uci_idr_mutex);
+	if (!udev) {
+		pr_err("uci dev: minor %d not found\n", minor);
+		ret = -ENODEV;
+		goto error_no_dev;
+	}
+
+	kref_get(&udev->ref_count);
+
+	mhi_dev = udev->mhi_dev;
+	dev = &mhi_dev->dev;
+
+	mutex_lock(&udev->lock);
+	if (!udev->enabled) {
+		dev_info(dev, "Node exist, but not in active state!\n");
+		goto error_open_chan;
+	}
+
+	if (!kref_get_unless_zero(&udev->open_count)) {
+		dev_dbg(dev, "Starting channel\n");
+		ret = mhi_prepare_for_transfer(udev->mhi_dev);
+		if (ret) {
+			dev_err(dev, "Error starting transfer channels\n");
+			goto error_open_chan;
+		}
+
+		ret = mhi_queue_inbound(udev);
+		if (ret)
+			goto error_rx_queue;
+
+		kref_init(&udev->open_count);
+	}
+
+	dev_dbg(dev, "Node open, ref counts %u\n",
+		kref_read(&udev->open_count));
+
+	filp->private_data = udev;
+	mutex_unlock(&udev->lock);
+
+	return 0;
+
+error_rx_queue:
+	dl_chan = &udev->dl_chan;
+	mhi_unprepare_from_transfer(udev->mhi_dev);
+	list_for_each_entry_safe(buf_itr, tmp, &dl_chan->pending, node) {
+		list_del(&buf_itr->node);
+		kfree(buf_itr->data);
+	}
+error_open_chan:
+	mutex_unlock(&udev->lock);
+	kref_put(&udev->ref_count, mhi_uci_dev_release);
+error_no_dev:
+	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->ul_chan;
+	struct device *dev = &mhi_dev->dev;
+
+	dev_dbg(dev, "status: %d xfer_len: %zu\n",
+		mhi_result->transaction_status, mhi_result->bytes_xferd);
+
+	kfree(mhi_result->buf_addr);
+
+	if (!mhi_result->transaction_status)
+		wake_up(&uchan->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->dl_chan;
+	struct device *dev = &mhi_dev->dev;
+	struct uci_buf *buf;
+
+	dev_dbg(dev, "status: %d receive_len: %zu\n",
+		mhi_result->transaction_status, mhi_result->bytes_xferd);
+
+	if (mhi_result->transaction_status == -ENOTCONN) {
+		kfree(mhi_result->buf_addr);
+		return;
+	}
+
+	spin_lock_bh(&uchan->lock);
+	buf = mhi_result->buf_addr + udev->actual_mtu;
+	buf->data = mhi_result->buf_addr;
+	buf->len = mhi_result->bytes_xferd;
+	list_add_tail(&buf->node, &uchan->pending);
+	spin_unlock_bh(&uchan->lock);
+
+	wake_up(&uchan->wq);
+}
+
+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, dir;
+
+	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(&udev->lock);
+
+	mutex_lock(&uci_idr_mutex);
+	index = idr_alloc(&uci_idr, udev, 0, MAX_UCI_MINORS, GFP_KERNEL);
+	mutex_unlock(&uci_idr_mutex);
+	if (index < 0) {
+		mutex_unlock(&udev->lock);
+		kfree(udev);
+		return index;
+	}
+
+	udev->minor = index;
+
+	/* 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_idr_mutex);
+		idr_remove(&uci_idr, udev->minor);
+		mutex_unlock(&uci_idr_mutex);
+		mutex_unlock(&udev->lock);
+		kfree(udev);
+		return PTR_ERR(dev);
+	}
+
+	for (dir = 0; dir < 2; dir++) {
+		struct uci_chan *uchan = (dir) ?
+			&udev->ul_chan : &udev->dl_chan;
+		spin_lock_init(&uchan->lock);
+		init_waitqueue_head(&uchan->wq);
+		INIT_LIST_HEAD(&uchan->pending);
+	}
+
+	udev->mtu = min_t(size_t, id->driver_data, MHI_MAX_MTU);
+	udev->actual_mtu = udev->mtu - sizeof(struct uci_buf);
+	dev_set_drvdata(&mhi_dev->dev, udev);
+	udev->enabled = true;
+
+	mutex_unlock(&udev->lock);
+
+	dev_info(&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);
+
+	mutex_lock(&udev->lock);
+
+	/* disable the node */
+	udev->enabled = false;
+
+	wake_up(&udev->dl_chan.wq);
+	wake_up(&udev->ul_chan.wq);
+
+	/* delete the node to prevent new opens */
+	device_destroy(uci_dev_class, MKDEV(uci_dev_major, udev->minor));
+
+	mutex_lock(&uci_idr_mutex);
+	idr_remove(&uci_idr, udev->minor);
+	mutex_unlock(&uci_idr_mutex);
+
+	mutex_unlock(&udev->lock);
+
+	kref_put(&udev->ref_count, mhi_uci_dev_release);
+}
+
+/* .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);
+		return -ENODEV;
+	}
+
+	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);
+}
+
+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 v5 4/4] bus: mhi: clients: Add userspace client interface driver

[Greg KH]

On Wed, Aug 05, 2020 at 11:41:03PM -0700, Hemant Kumar wrote:
> This MHI client driver allows userspace clients to transfer
> raw data between MHI device and host using standard file operations.
> 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@codeaurora.org>
> ---
>  drivers/bus/mhi/Kconfig          |   6 +
>  drivers/bus/mhi/Makefile         |   1 +
>  drivers/bus/mhi/clients/Kconfig  |  15 +

Why a whole new subdirectory for just one file?

Please keep it in the same directory until you get too many different
files.

>  drivers/bus/mhi/clients/Makefile |   3 +
>  drivers/bus/mhi/clients/uci.c    | 662 +++++++++++++++++++++++++++++++++++++++
>  5 files changed, 687 insertions(+)
>  create mode 100644 drivers/bus/mhi/clients/Kconfig
>  create mode 100644 drivers/bus/mhi/clients/Makefile
>  create mode 100644 drivers/bus/mhi/clients/uci.c
> 
> diff --git a/drivers/bus/mhi/Kconfig b/drivers/bus/mhi/Kconfig
> index 6a217ff..927c392 100644
> --- a/drivers/bus/mhi/Kconfig
> +++ b/drivers/bus/mhi/Kconfig
> @@ -20,3 +20,9 @@ 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.
> +
> +if MHI_BUS
> +
> +source "drivers/bus/mhi/clients/Kconfig"
> +
> +endif
> diff --git a/drivers/bus/mhi/Makefile b/drivers/bus/mhi/Makefile
> index 19e6443..48f6028 100644
> --- a/drivers/bus/mhi/Makefile
> +++ b/drivers/bus/mhi/Makefile
> @@ -1,2 +1,3 @@
>  # core layer
>  obj-y += core/
> +obj-y += clients/
> diff --git a/drivers/bus/mhi/clients/Kconfig b/drivers/bus/mhi/clients/Kconfig
> new file mode 100644
> index 0000000..37aaf51
> --- /dev/null
> +++ b/drivers/bus/mhi/clients/Kconfig
> @@ -0,0 +1,15 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +menu "MHI clients support"
> +
> +config MHI_UCI
> +       tristate "MHI UCI"
> +       depends on MHI_BUS
> +       help
> +	 MHI based userspace client interface driver is used for transferring
> +	 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.
> +

Module name information?


> +endmenu
> diff --git a/drivers/bus/mhi/clients/Makefile b/drivers/bus/mhi/clients/Makefile
> new file mode 100644
> index 0000000..cd34282
> --- /dev/null
> +++ b/drivers/bus/mhi/clients/Makefile
> @@ -0,0 +1,3 @@
> +# SPDX-License-Identifier: GPL-2.0-only
> +
> +obj-$(CONFIG_MHI_UCI) += uci.o

Why not mhi_ as a prefix?  This is a very generic module name, right?

> diff --git a/drivers/bus/mhi/clients/uci.c b/drivers/bus/mhi/clients/uci.c
> new file mode 100644
> index 0000000..a25d5d0
> --- /dev/null
> +++ b/drivers/bus/mhi/clients/uci.c
> @@ -0,0 +1,662 @@
> +// 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)
> +
> +static DEFINE_IDR(uci_idr);
> +static DEFINE_MUTEX(uci_idr_mutex);
> +static struct class *uci_dev_class;
> +static int uci_dev_major = -1;

Why init this to -1?

> +
> +/**
> + * struct uci_chan - MHI channel for a uci device
> + * @wq: wait queue for reader/writer
> + * @lock: spin lock
> + * @pending: list of rx buffers userspace is waiting to read
> + * @cur_buf: current buffer userspace is reading
> + * @rx_size: size of the current rx buffer userspace is reading
> + */
> +struct uci_chan {
> +	wait_queue_head_t wq;
> +
> +	/* protects pending and cur_buf members */
> +	spinlock_t lock;
> +
> +	struct list_head pending;
> +	struct uci_buf *cur_buf;
> +	size_t rx_size;
> +};
> +
> +/**
> + * 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
> + * @chan: MHI channel name
> + * @lock: mutex lock
> + * @ul_chan: uplink uci channel object
> + * @dl_chan: downlink uci channel object
> + * @mtu: max tx buffer length
> + * @actual_mtu: maximum size of incoming buffer
> + * @ref_count: uci_dev reference count
> + * @open_count: device node open count
> + * @enabled: uci device probed
> + */
> +struct uci_dev {
> +	unsigned int minor;
> +	struct mhi_device *mhi_dev;
> +	const char *chan;
> +
> +	/* protects uci_dev struct members */
> +	struct mutex lock;
> +
> +	struct uci_chan ul_chan;
> +	struct uci_chan dl_chan;
> +	size_t mtu;
> +	size_t actual_mtu;
> +	struct kref ref_count;
> +	struct kref open_count;

I'm stopping right here.  A structure can only have ONE reference count
to control its lifespan.  You have 2 here, which guarantees that either
you are using a kref incorrectly, or your code is totally confused and
will break easily.

Please fix this as this is not how to do this.

Also, why does anyone need to care about the number of times that open()
is called?  The vfs layer should handle all of that for you, right?

No other misc driver has to deal with this multi-layered reference
counting, so perhaps you are making this a lot more complex than it
really has to be?

thanks,

greg k-h

Re: [PATCH v5 4/4] bus: mhi: clients: Add userspace client interface driver

[Hemant Kumar]

Hi Greg,

On 9/7/20 2:37 AM, Greg KH wrote:
> On Wed, Aug 05, 2020 at 11:41:03PM -0700, Hemant Kumar wrote:
>> This MHI client driver allows userspace clients to transfer
>> raw data between MHI device and host using standard file operations.
>> 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@codeaurora.org>
>> ---
>>   drivers/bus/mhi/Kconfig          |   6 +
>>   drivers/bus/mhi/Makefile         |   1 +
>>   drivers/bus/mhi/clients/Kconfig  |  15 +
> 
> Why a whole new subdirectory for just one file?
> 
> Please keep it in the same directory until you get too many different
> files.
Currently MHI core driver files are under bus/mhi/core. Since MHI 
clients sit on top of core layer of MHI driver, i can move uci.c 
directly under /bus/mhi/.

> 
>>   drivers/bus/mhi/clients/Makefile |   3 +
>>   drivers/bus/mhi/clients/uci.c    | 662 +++++++++++++++++++++++++++++++++++++++
>>   5 files changed, 687 insertions(+)
>>   create mode 100644 drivers/bus/mhi/clients/Kconfig
>>   create mode 100644 drivers/bus/mhi/clients/Makefile
>>   create mode 100644 drivers/bus/mhi/clients/uci.c
>>
>> diff --git a/drivers/bus/mhi/Kconfig b/drivers/bus/mhi/Kconfig
>> index 6a217ff..927c392 100644
>> --- a/drivers/bus/mhi/Kconfig
>> +++ b/drivers/bus/mhi/Kconfig
>> @@ -20,3 +20,9 @@ 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.
>> +
>> +if MHI_BUS
>> +
>> +source "drivers/bus/mhi/clients/Kconfig"
>> +
>> +endif
>> diff --git a/drivers/bus/mhi/Makefile b/drivers/bus/mhi/Makefile
>> index 19e6443..48f6028 100644
>> --- a/drivers/bus/mhi/Makefile
>> +++ b/drivers/bus/mhi/Makefile
>> @@ -1,2 +1,3 @@
>>   # core layer
>>   obj-y += core/
>> +obj-y += clients/
>> diff --git a/drivers/bus/mhi/clients/Kconfig b/drivers/bus/mhi/clients/Kconfig
>> new file mode 100644
>> index 0000000..37aaf51
>> --- /dev/null
>> +++ b/drivers/bus/mhi/clients/Kconfig
>> @@ -0,0 +1,15 @@
>> +# SPDX-License-Identifier: GPL-2.0-only
>> +
>> +menu "MHI clients support"
>> +
>> +config MHI_UCI
>> +       tristate "MHI UCI"
>> +       depends on MHI_BUS
>> +       help
>> +	 MHI based userspace client interface driver is used for transferring
>> +	 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.
>> +
> 
> Module name information?
Thanks for pointing it out, will add in next patch set.
> 
> 
>> +endmenu
>> diff --git a/drivers/bus/mhi/clients/Makefile b/drivers/bus/mhi/clients/Makefile
>> new file mode 100644
>> index 0000000..cd34282
>> --- /dev/null
>> +++ b/drivers/bus/mhi/clients/Makefile
>> @@ -0,0 +1,3 @@
>> +# SPDX-License-Identifier: GPL-2.0-only
>> +
>> +obj-$(CONFIG_MHI_UCI) += uci.o
> 
> Why not mhi_ as a prefix?  This is a very generic module name, right?
how about adding
mhi_uci-y		:= uci.o
obj-$(CONFIG_MHI_UCI)	+= mhi_uci.o

> 
>> diff --git a/drivers/bus/mhi/clients/uci.c b/drivers/bus/mhi/clients/uci.c
>> new file mode 100644
>> index 0000000..a25d5d0
>> --- /dev/null
>> +++ b/drivers/bus/mhi/clients/uci.c
>> @@ -0,0 +1,662 @@
>> +// 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)
>> +
>> +static DEFINE_IDR(uci_idr);
>> +static DEFINE_MUTEX(uci_idr_mutex);
>> +static struct class *uci_dev_class;
>> +static int uci_dev_major = -1;
> 
> Why init this to -1?
Idea was to initialize with invalid value, i can leave it zero initialized.
> 
>> +
>> +/**
>> + * struct uci_chan - MHI channel for a uci device
>> + * @wq: wait queue for reader/writer
>> + * @lock: spin lock
>> + * @pending: list of rx buffers userspace is waiting to read
>> + * @cur_buf: current buffer userspace is reading
>> + * @rx_size: size of the current rx buffer userspace is reading
>> + */
>> +struct uci_chan {
>> +	wait_queue_head_t wq;
>> +
>> +	/* protects pending and cur_buf members */
>> +	spinlock_t lock;
>> +
>> +	struct list_head pending;
>> +	struct uci_buf *cur_buf;
>> +	size_t rx_size;
>> +};
>> +
>> +/**
>> + * 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
>> + * @chan: MHI channel name
>> + * @lock: mutex lock
>> + * @ul_chan: uplink uci channel object
>> + * @dl_chan: downlink uci channel object
>> + * @mtu: max tx buffer length
>> + * @actual_mtu: maximum size of incoming buffer
>> + * @ref_count: uci_dev reference count
>> + * @open_count: device node open count
>> + * @enabled: uci device probed
>> + */
>> +struct uci_dev {
>> +	unsigned int minor;
>> +	struct mhi_device *mhi_dev;
>> +	const char *chan;
>> +
>> +	/* protects uci_dev struct members */
>> +	struct mutex lock;
>> +
>> +	struct uci_chan ul_chan;
>> +	struct uci_chan dl_chan;
>> +	size_t mtu;
>> +	size_t actual_mtu;
>> +	struct kref ref_count;
>> +	struct kref open_count;
> 
> I'm stopping right here.  A structure can only have ONE reference count
> to control its lifespan.  You have 2 here, which guarantees that either
> you are using a kref incorrectly, or your code is totally confused and
> will break easily.
> 
> Please fix this as this is not how to do this.
> 
> Also, why does anyone need to care about the number of times that open()
> is called?  The vfs layer should handle all of that for you, right?
Reason for using open_count was to allow start MHI channel only when 
first open() was called and stop the MHI channel when last release() is 
called. Since uci driver just need to handle one open() from user space
other calls to open can simply return -EBUSY. i will get rid of 
open_count and does not let multiple threads to open same file node.
> 
> No other misc driver has to deal with this multi-layered reference
> counting, so perhaps you are making this a lot more complex than it
> really has to be?
> 
> thanks,
> 
> greg k-h
> 

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a Linux Foundation Collaborative Project

Re: [PATCH v5 4/4] bus: mhi: clients: Add userspace client interface driver

[Greg KH]

On Fri, Sep 11, 2020 at 06:28:02AM +0000, Hemant Kumar wrote:
> > > +struct uci_dev {
> > > +	unsigned int minor;
> > > +	struct mhi_device *mhi_dev;
> > > +	const char *chan;
> > > +
> > > +	/* protects uci_dev struct members */
> > > +	struct mutex lock;
> > > +
> > > +	struct uci_chan ul_chan;
> > > +	struct uci_chan dl_chan;
> > > +	size_t mtu;
> > > +	size_t actual_mtu;
> > > +	struct kref ref_count;
> > > +	struct kref open_count;
> > 
> > I'm stopping right here.  A structure can only have ONE reference count
> > to control its lifespan.  You have 2 here, which guarantees that either
> > you are using a kref incorrectly, or your code is totally confused and
> > will break easily.
> > 
> > Please fix this as this is not how to do this.
> > 
> > Also, why does anyone need to care about the number of times that open()
> > is called?  The vfs layer should handle all of that for you, right?
> Reason for using open_count was to allow start MHI channel only when first
> open() was called and stop the MHI channel when last release() is called.
> Since uci driver just need to handle one open() from user space
> other calls to open can simply return -EBUSY. i will get rid of open_count
> and does not let multiple threads to open same file node.

You will fail in trying to attempt only one open on your device node,
sorry.  You can properly trigger off of the first/last things, but
having two different reference counts is NOT how to do this, those are
to control the lifetime of a structure/object.

greg k-h

Re: [PATCH v5 0/4] user space client interface driver

[Hemant Kumar]

Hi Jeff and Mani,
On 8/5/20 11:40 PM, Hemant Kumar wrote:
> 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 (4):
>    bus: mhi: core: Add helper API to return number of free TREs
>    bus: mhi: core: Move MHI_MAX_MTU to external header file
>    docs: Add documentation for userspace client interface
>    bus: mhi: clients: Add userspace client interface driver
> 
>   Documentation/mhi/index.rst      |   1 +
>   Documentation/mhi/uci.rst        |  39 +++
>   drivers/bus/mhi/Kconfig          |   6 +
>   drivers/bus/mhi/Makefile         |   1 +
>   drivers/bus/mhi/clients/Kconfig  |  15 +
>   drivers/bus/mhi/clients/Makefile |   3 +
>   drivers/bus/mhi/clients/uci.c    | 662 +++++++++++++++++++++++++++++++++++++++
>   drivers/bus/mhi/core/internal.h  |   1 -
>   drivers/bus/mhi/core/main.c      |  12 +
>   include/linux/mhi.h              |  12 +
>   10 files changed, 751 insertions(+), 1 deletion(-)
>   create mode 100644 Documentation/mhi/uci.rst
>   create mode 100644 drivers/bus/mhi/clients/Kconfig
>   create mode 100644 drivers/bus/mhi/clients/Makefile
>   create mode 100644 drivers/bus/mhi/clients/uci.c
> 

Could you please review my changes on V5? I tried addressing Greg's 
comment and would need help getting it reviewed from other contributors 
to MHI driver as well.

Thanks,
Hemant
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a Linux Foundation Collaborative Project