[PATCH] soundwire: add slave status as a sysfs file

[Vinod Koul <vkoul@kernel.org>]

SoundWire Slave status is not reported in the sysfs, so add this file
with string values for status to userspace. Users can look into this
file to see the Slave status at that point of time.

Signed-off-by: Vinod Koul <vkoul@kernel.org>
---
On RB3 it shows as:
root@linaro-alip:/sys/bus/soundwire/devices# cat sdw:0:217:2010:0:1/status
Attached
root@linaro-alip:/sys/bus/soundwire/devices# cat sdw:0:217:2010:0:2/status
Attached

 .../ABI/testing/sysfs-bus-soundwire-slave       |  7 +++++++
 drivers/soundwire/sysfs_slave.c                 | 17 +++++++++++++++++
 include/linux/soundwire/sdw.h                   |  2 ++
 3 files changed, 26 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-soundwire-slave b/Documentation/ABI/testing/sysfs-bus-soundwire-slave
index db4c9511d1aa..8a64f8e9079a 100644
--- a/Documentation/ABI/testing/sysfs-bus-soundwire-slave
+++ b/Documentation/ABI/testing/sysfs-bus-soundwire-slave
@@ -89,3 +89,10 @@ Description:	SoundWire Slave Data Source/Sink Port-N DisCo properties.
 		for SoundWire. They define various properties of the
 		Source/Sink Data port N and are used by the bus to configure
 		the Data Port N.
+
+What:		/sys/bus/soundwire/devices/sdw:.../status
+Date:		September 2020
+Contact:	Vinod Koul <vkoul@kernel.org>
+Description:	Soundwire Slave status
+		This reports the current status of the slave, e.g if it is
+		UNATTACHED, Attached, Alert or Reserved
diff --git a/drivers/soundwire/sysfs_slave.c b/drivers/soundwire/sysfs_slave.c
index f510071b0add..3d2cc7612d0d 100644
--- a/drivers/soundwire/sysfs_slave.c
+++ b/drivers/soundwire/sysfs_slave.c
@@ -97,8 +97,25 @@ static ssize_t modalias_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(modalias);
 
+static const char *const slave_status[SDW_SLAVE_MAX] = {
+	[SDW_SLAVE_UNATTACHED] =  "UNATTACHED",
+	[SDW_SLAVE_ATTACHED] = "Attached",
+	[SDW_SLAVE_ALERT] = "Alert",
+	[SDW_SLAVE_RESERVED] = "Reserved",
+};
+
+static ssize_t status_show(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct sdw_slave *slave = dev_to_sdw_dev(dev);
+
+	return sprintf(buf, "%s\n", slave_status[slave->status]);
+}
+static DEVICE_ATTR_RO(status);
+
 static struct attribute *slave_attrs[] = {
 	&dev_attr_modalias.attr,
+	&dev_attr_status.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(slave);
diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
index 790823d2d33b..e8c9c20d38b0 100644
--- a/include/linux/soundwire/sdw.h
+++ b/include/linux/soundwire/sdw.h
@@ -73,12 +73,14 @@ enum {
  * @SDW_SLAVE_ATTACHED: Slave is attached with bus.
  * @SDW_SLAVE_ALERT: Some alert condition on the Slave
  * @SDW_SLAVE_RESERVED: Reserved for future use
+ * @SDW_SLAVE_MAX: Last status value
  */
 enum sdw_slave_status {
 	SDW_SLAVE_UNATTACHED = 0,
 	SDW_SLAVE_ATTACHED = 1,
 	SDW_SLAVE_ALERT = 2,
 	SDW_SLAVE_RESERVED = 3,
+	SDW_SLAVE_MAX,
 };
 
 /**
-- 
2.26.2