soundwire: master: add sysfs support

Add the master properties as attributes. The description is directly
derived from the MIPI DisCo specification.

Credits: this patch is based on an earlier internal contribution by
Vinod Koul, Sanyog Kale, Shreyas Nc and Hardik Shah.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20200518203551.2053-3-yung-chuan.liao@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

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

+What:		/sys/bus/soundwire/devices/sdw-master-N/revision
+		/sys/bus/soundwire/devices/sdw-master-N/clk_stop_modes
+		/sys/bus/soundwire/devices/sdw-master-N/clk_freq
+		/sys/bus/soundwire/devices/sdw-master-N/clk_gears
+		/sys/bus/soundwire/devices/sdw-master-N/default_col
+		/sys/bus/soundwire/devices/sdw-master-N/default_frame_rate
+		/sys/bus/soundwire/devices/sdw-master-N/default_row
+		/sys/bus/soundwire/devices/sdw-master-N/dynamic_shape
+		/sys/bus/soundwire/devices/sdw-master-N/err_threshold
+		/sys/bus/soundwire/devices/sdw-master-N/max_clk_freq
+
+Date:		April 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 Master-N DisCo properties.
+		These properties are defined by MIPI DisCo Specification
+		for SoundWire. They define various properties of the Master
+		and are used by the bus to configure the Master. clk_stop_modes
+		is a bitmask for simplifications and combines the
+		clock-stop-mode0 and clock-stop-mode1 properties.

drivers/soundwire/master.c

@@ -8,6 +8,89 @@
 #include <linux/soundwire/sdw_type.h>
 #include "bus.h"
 
+/*
+ * The sysfs for properties reflects the MIPI description as given
+ * in the MIPI DisCo spec
+ *
+ * Base file is:
+ *	sdw-master-N
+ *      |---- revision
+ *      |---- clk_stop_modes
+ *      |---- max_clk_freq
+ *      |---- clk_freq
+ *      |---- clk_gears
+ *      |---- default_row
+ *      |---- default_col
+ *      |---- dynamic_shape
+ *      |---- err_threshold
+ */
+
+#define sdw_master_attr(field, format_string)				\
+static ssize_t field##_show(struct device *dev,				\
+			    struct device_attribute *attr,		\
+			    char *buf)					\
+{									\
+	struct sdw_master_device *md = dev_to_sdw_master_device(dev);	\
+	return sprintf(buf, format_string, md->bus->prop.field);	\
+}									\
+static DEVICE_ATTR_RO(field)
+
+sdw_master_attr(revision, "0x%x\n");
+sdw_master_attr(clk_stop_modes, "0x%x\n");
+sdw_master_attr(max_clk_freq, "%d\n");
+sdw_master_attr(default_row, "%d\n");
+sdw_master_attr(default_col, "%d\n");
+sdw_master_attr(default_frame_rate, "%d\n");
+sdw_master_attr(dynamic_frame, "%d\n");
+sdw_master_attr(err_threshold, "%d\n");
+
+static ssize_t clock_frequencies_show(struct device *dev,
+				      struct device_attribute *attr, char *buf)
+{
+	struct sdw_master_device *md = dev_to_sdw_master_device(dev);
+	ssize_t size = 0;
+	int i;
+
+	for (i = 0; i < md->bus->prop.num_clk_freq; i++)
+		size += sprintf(buf + size, "%8d ",
+				md->bus->prop.clk_freq[i]);
+	size += sprintf(buf + size, "\n");
+
+	return size;
+}
+static DEVICE_ATTR_RO(clock_frequencies);
+
+static ssize_t clock_gears_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct sdw_master_device *md = dev_to_sdw_master_device(dev);
+	ssize_t size = 0;
+	int i;
+
+	for (i = 0; i < md->bus->prop.num_clk_gears; i++)
+		size += sprintf(buf + size, "%8d ",
+				md->bus->prop.clk_gears[i]);
+	size += sprintf(buf + size, "\n");
+
+	return size;
+}
+static DEVICE_ATTR_RO(clock_gears);
+
+static struct attribute *master_node_attrs[] = {
+	&dev_attr_revision.attr,
+	&dev_attr_clk_stop_modes.attr,
+	&dev_attr_max_clk_freq.attr,
+	&dev_attr_default_row.attr,
+	&dev_attr_default_col.attr,
+	&dev_attr_default_frame_rate.attr,
+	&dev_attr_dynamic_frame.attr,
+	&dev_attr_err_threshold.attr,
+	&dev_attr_clock_frequencies.attr,
+	&dev_attr_clock_gears.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(master_node);
+
 static void sdw_master_device_release(struct device *dev)
 {
 	struct sdw_master_device *md = dev_to_sdw_master_device(dev);
@@ -48,6 +131,7 @@ int sdw_master_device_add(struct sdw_bus *bus, struct device *parent,
 	md->dev.bus = &sdw_bus_type;
 	md->dev.type = &sdw_master_type;
 	md->dev.parent = parent;
+	md->dev.groups = master_node_groups;
 	md->dev.of_node = parent->of_node;
 	md->dev.fwnode = fwnode;
 	md->dev.dma_mask = parent->dma_mask;