[PATCH] bus: mhi: core: Introduce sysfs ul chan id for mhi chan device

[carl.yin@quectel.com]

From: "carl.yin" <carl.yin@quectel.com>

User space software like ModemManager can identify the function
of the mhi chan device by ul_chan_id.

Signed-off-by: carl.yin <carl.yin@quectel.com>
---
 Documentation/ABI/stable/sysfs-bus-mhi | 10 ++++++++++
 drivers/bus/mhi/core/init.c            | 15 +++++++++++++++
 2 files changed, 25 insertions(+)

diff --git a/Documentation/ABI/stable/sysfs-bus-mhi b/Documentation/ABI/stable/sysfs-bus-mhi
index ecfe766..6d52768 100644
--- a/Documentation/ABI/stable/sysfs-bus-mhi
+++ b/Documentation/ABI/stable/sysfs-bus-mhi
@@ -19,3 +19,13 @@ Description:	The file holds the OEM PK Hash value of the endpoint device
 		read without having the device power on at least once, the file
 		will read all 0's.
 Users:		Any userspace application or clients interested in device info.
+
+What:		/sys/bus/mhi/devices/.../ul_chan_id
+Date:		November 2020
+KernelVersion:	5.10
+Contact:	Carl Yin <carl.yin@quectel.com>
+Description:	The file holds the uplink chan id of the mhi chan device.
+		User space software like ModemManager can identify the function of
+		the mhi chan device. If the mhi device is not a chan device,
+		eg mhi controller device, the file read -1.
+Users:		Any userspace application or clients interested in device info.
diff --git a/drivers/bus/mhi/core/init.c b/drivers/bus/mhi/core/init.c
index c6b43e9..ac4aa5c 100644
--- a/drivers/bus/mhi/core/init.c
+++ b/drivers/bus/mhi/core/init.c
@@ -105,9 +105,24 @@ static ssize_t oem_pk_hash_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(oem_pk_hash);
 
+static ssize_t ul_chan_id_show(struct device *dev,
+				struct device_attribute *attr,
+				char *buf)
+{
+	struct mhi_device *mhi_dev = to_mhi_device(dev);
+	int ul_chan_id = -1;
+
+	if (mhi_dev->ul_chan)
+		ul_chan_id = mhi_dev->ul_chan_id;
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", ul_chan_id);
+}
+static DEVICE_ATTR_RO(ul_chan_id);
+
 static struct attribute *mhi_dev_attrs[] = {
 	&dev_attr_serial_number.attr,
 	&dev_attr_oem_pk_hash.attr,
+	&dev_attr_ul_chan_id.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(mhi_dev);
-- 
2.25.1