[PATCH 2/2] soundwire: Assume default maximum valid channel if not specified

[Charles Keepax <ckeepax@opensource.cirrus.com>]

The SDCA specification defines all the supported channel properties
as optional and states that in the case none are specified defaults
of min_ch=0 and max_ch=7 should be used. If both properties are
not present in the DisCo the current code results in min_ch=0 and
max_ch=0. As min_ch and max_ch are both channel indexes, users can't
discern if they should interpret this as the default case (1-8
channels supported) or the DisCo specified a single valid channel of
0 (1 channel supported).

In the case there are no valid supported channel properties populate
max_ch with 7 as the specification suggests, to avoid the ambiguity.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
---
 drivers/soundwire/mipi_disco.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/soundwire/mipi_disco.c b/drivers/soundwire/mipi_disco.c
index 259ad98b5b7a9..eadbda55f377f 100644
--- a/drivers/soundwire/mipi_disco.c
+++ b/drivers/soundwire/mipi_disco.c
@@ -284,12 +284,6 @@ static int sdw_slave_read_dpn(struct sdw_slave *slave,
 				"mipi-sdw-imp-def-dpn-interrupts-supported",
 				&dpn[i].imp_def_interrupts);
 
-		fwnode_property_read_u32(node, "mipi-sdw-min-channel-number",
-					 &dpn[i].min_ch);
-
-		fwnode_property_read_u32(node, "mipi-sdw-max-channel-number",
-					 &dpn[i].max_ch);
-
 		nval = fwnode_property_count_u32(node, "mipi-sdw-channel-number-list");
 		if (nval > 0) {
 			dpn[i].num_channels = nval;
@@ -309,6 +303,14 @@ static int sdw_slave_read_dpn(struct sdw_slave *slave,
 				return ret;
 		}
 
+		fwnode_property_read_u32(node, "mipi-sdw-min-channel-number",
+					 &dpn[i].min_ch);
+
+		ret = fwnode_property_read_u32(node, "mipi-sdw-max-channel-number",
+					       &dpn[i].max_ch);
+		if (ret && !dpn[i].num_channels)
+			dpn[i].max_ch = 7;
+
 		nval = fwnode_property_count_u32(node, "mipi-sdw-channel-combination-list");
 		if (nval > 0) {
 			dpn[i].num_ch_combinations = nval;
-- 
2.47.3