Soundwire: add sdw_slave_get_scale_index helper

Currently, we only set peripheral frequency when the peripheral is
initialized. However, curr_dr_freq may change to get required bandwidth.
For example, curr_dr_freq may increase from 4.8MHz to 9.6MHz when the
4th stream is opened. Add a helper to get the scale index so that we can
get the scale index and program it.

Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20241218080155.102405-7-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/bus.c

@@ -1276,23 +1276,12 @@ int sdw_configure_dpn_intr(struct sdw_slave *slave,
 	return ret;
 }
 
-static int sdw_slave_set_frequency(struct sdw_slave *slave)
+int sdw_slave_get_scale_index(struct sdw_slave *slave, u8 *base)
 {
 	u32 mclk_freq = slave->bus->prop.mclk_freq;
 	u32 curr_freq = slave->bus->params.curr_dr_freq >> 1;
 	unsigned int scale;
 	u8 scale_index;
-	u8 base;
-	int ret;
-
-	/*
-	 * frequency base and scale registers are required for SDCA
-	 * devices. They may also be used for 1.2+/non-SDCA devices.
-	 * Driver can set the property, we will need a DisCo property
-	 * to discover this case from platform firmware.
-	 */
-	if (!slave->id.class_id && !slave->prop.clock_reg_supported)
-		return 0;
 
 	if (!mclk_freq) {
 		dev_err(&slave->dev,
@@ -1311,19 +1300,19 @@ static int sdw_slave_set_frequency(struct sdw_slave *slave)
 	 */
 	if (!(19200000 % mclk_freq)) {
 		mclk_freq = 19200000;
-		base = SDW_SCP_BASE_CLOCK_19200000_HZ;
+		*base = SDW_SCP_BASE_CLOCK_19200000_HZ;
 	} else if (!(22579200 % mclk_freq)) {
 		mclk_freq = 22579200;
-		base = SDW_SCP_BASE_CLOCK_22579200_HZ;
+		*base = SDW_SCP_BASE_CLOCK_22579200_HZ;
 	} else if (!(24576000 % mclk_freq)) {
 		mclk_freq = 24576000;
-		base = SDW_SCP_BASE_CLOCK_24576000_HZ;
+		*base = SDW_SCP_BASE_CLOCK_24576000_HZ;
 	} else if (!(32000000 % mclk_freq)) {
 		mclk_freq = 32000000;
-		base = SDW_SCP_BASE_CLOCK_32000000_HZ;
+		*base = SDW_SCP_BASE_CLOCK_32000000_HZ;
 	} else if (!(96000000 % mclk_freq)) {
 		mclk_freq = 24000000;
-		base = SDW_SCP_BASE_CLOCK_24000000_HZ;
+		*base = SDW_SCP_BASE_CLOCK_24000000_HZ;
 	} else {
 		dev_err(&slave->dev,
 			"Unsupported clock base, mclk %d\n",
@@ -1354,6 +1343,34 @@ static int sdw_slave_set_frequency(struct sdw_slave *slave)
 	}
 	scale_index++;
 
+	dev_dbg(&slave->dev,
+		"Configured bus base %d, scale %d, mclk %d, curr_freq %d\n",
+		*base, scale_index, mclk_freq, curr_freq);
+
+	return scale_index;
+}
+EXPORT_SYMBOL(sdw_slave_get_scale_index);
+
+static int sdw_slave_set_frequency(struct sdw_slave *slave)
+{
+	int scale_index;
+	u8 base;
+	int ret;
+
+	/*
+	 * frequency base and scale registers are required for SDCA
+	 * devices. They may also be used for 1.2+/non-SDCA devices.
+	 * Driver can set the property directly, for now there's no
+	 * DisCo property to discover support for the scaling registers
+	 * from platform firmware.
+	 */
+	if (!slave->id.class_id && !slave->prop.clock_reg_supported)
+		return 0;
+
+	scale_index = sdw_slave_get_scale_index(slave, &base);
+	if (scale_index < 0)
+		return scale_index;
+
 	ret = sdw_write_no_pm(slave, SDW_SCP_BUS_CLOCK_BASE, base);
 	if (ret < 0) {
 		dev_err(&slave->dev,
@@ -1373,10 +1390,6 @@ static int sdw_slave_set_frequency(struct sdw_slave *slave)
 		dev_err(&slave->dev,
 			"SDW_SCP_BUSCLOCK_SCALE_B1 write failed:%d\n", ret);
 
-	dev_dbg(&slave->dev,
-		"Configured bus base %d, scale %d, mclk %d, curr_freq %d\n",
-		base, scale_index, mclk_freq, curr_freq);
-
 	return ret;
 }
 

include/linux/soundwire/sdw.h

@@ -1052,6 +1052,8 @@ int sdw_stream_add_slave(struct sdw_slave *slave,
 int sdw_stream_remove_slave(struct sdw_slave *slave,
 			    struct sdw_stream_runtime *stream);
 
+int sdw_slave_get_scale_index(struct sdw_slave *slave, u8 *base);
+
 /* messaging and data APIs */
 int sdw_read(struct sdw_slave *slave, u32 addr);
 int sdw_write(struct sdw_slave *slave, u32 addr, u8 value);