soundwire: sysfs: add slave status and device number before probe

The MIPI DisCo device properties that are read by the driver from
platform firmware, or hard-coded in the driver, should only be
provided as sysfs entries when a driver probes successfully.

However the device status and device number is updated even when there
is no driver present, and hence can be updated when a Slave device is
detected on the bus without being described in platform firmware and
without any driver registered/probed.

As suggested by GregKH, the attribute group for Slave status and
device number is is added by default upon device registration.

Credits to Vinod Koul for the status_show() function, shared in a
separate patch and used as is here. The status table was modified to
remove an unnecessary enum and status_show() is handled in a different
group attribute than what was suggested by Vinod.
Tested-by: Srinivas Kandgatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Co-developed-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20200924194430.121058-3-pierre-louis.bossart@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

Documentation/ABI/testing/sysfs-bus-soundwire-slave

+What:		/sys/bus/soundwire/devices/sdw:.../status
+		/sys/bus/soundwire/devices/sdw:.../device_number
+
+Date:		September 2020
+
+Contact:	Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
+		Bard Liao <yung-chuan.liao@linux.intel.com>
+		Vinod Koul <vkoul@kernel.org>
+
+Description:	SoundWire Slave status
+
+		These properties report the Slave status, e.g. if it
+		is UNATTACHED or not, and in the latter case show the
+		device_number. This status information is useful to
+		detect devices exposed by platform firmware but not
+		physically present on the bus, and conversely devices
+		not exposed in platform firmware but enumerated.
+
 What:		/sys/bus/soundwire/devices/sdw:.../dev-properties/mipi_revision
 		/sys/bus/soundwire/devices/sdw:.../dev-properties/wake_capable
 		/sys/bus/soundwire/devices/sdw:.../dev-properties/test_mode_capable

drivers/soundwire/slave.c

@@ -6,6 +6,7 @@
 #include <linux/soundwire/sdw.h>
 #include <linux/soundwire/sdw_type.h>
 #include "bus.h"
+#include "sysfs_local.h"
 
 static void sdw_slave_release(struct device *dev)
 {
@@ -51,6 +52,7 @@ int sdw_slave_add(struct sdw_bus *bus,
 	slave->dev.bus = &sdw_bus_type;
 	slave->dev.of_node = of_node_get(to_of_node(fwnode));
 	slave->dev.type = &sdw_slave_type;
+	slave->dev.groups = sdw_slave_status_attr_groups;
 	slave->bus = bus;
 	slave->status = SDW_SLAVE_UNATTACHED;
 	init_completion(&slave->enumeration_complete);

drivers/soundwire/sysfs_local.h

@@ -8,6 +8,10 @@
  * SDW sysfs APIs -
  */
 
+/* basic attributes to report status of Slave (attachment, dev_num) */
+extern const struct attribute_group *sdw_slave_status_attr_groups[];
+
+/* additional device-managed properties reported after driver probe */
 int sdw_slave_sysfs_init(struct sdw_slave *slave);
 int sdw_slave_sysfs_dpn_init(struct sdw_slave *slave);
 

drivers/soundwire/sysfs_slave.c

@@ -16,9 +16,13 @@
 
 /*
  * The sysfs for Slave reflects the MIPI description as given
- * in the MIPI DisCo spec
+ * in the MIPI DisCo spec.
+ * status and device_number come directly from the MIPI SoundWire
+ * 1.x specification.
  *
  * Base file is device
+ *	|---- status
+ *	|---- device_number
  *	|---- modalias
  *	|---- dev-properties
  *		|---- mipi_revision
@@ -212,3 +216,55 @@ int sdw_slave_sysfs_init(struct sdw_slave *slave)
 
 	return 0;
 }
+
+/*
+ * the status is shown in capital letters for UNATTACHED and RESERVED
+ * on purpose, to highligh users to the fact that these status values
+ * are not expected.
+ */
+static const char *const slave_status[] = {
+	[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 ssize_t device_number_show(struct device *dev,
+				  struct device_attribute *attr, char *buf)
+{
+	struct sdw_slave *slave = dev_to_sdw_dev(dev);
+
+	if (slave->status == SDW_SLAVE_UNATTACHED)
+		return sprintf(buf, "%s", "N/A");
+	else
+		return sprintf(buf, "%d", slave->dev_num);
+}
+static DEVICE_ATTR_RO(device_number);
+
+static struct attribute *slave_status_attrs[] = {
+	&dev_attr_status.attr,
+	&dev_attr_device_number.attr,
+	NULL,
+};
+
+/*
+ * we don't use ATTRIBUTES_GROUP here since the group is used in a
+ * separate file and can't be handled as a static.
+ */
+static const struct attribute_group sdw_slave_status_attr_group = {
+	.attrs	= slave_status_attrs,
+};
+
+const struct attribute_group *sdw_slave_status_attr_groups[] = {
+	&sdw_slave_status_attr_group,
+	NULL
+};