[PATCH] drm: Fix DSC BPP increment decoding

[Imre Deak]

Starting with DPCD version 2.0 bits 6:3 of the DP_DSC_BITS_PER_PIXEL_INC
DPCD register contains the NativeYCbCr422_MAX_bpp_DELTA field, which can
be non-zero as opposed to earlier DPCD versions, hence decoding the
bit_per_pixel increment value at bits 2:0 in the same register requires
applying a mask, do so.

Cc: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
Fixes: 0c2287c96521 ("drm/display/dp: Add helper function to get DSC bpp precision")
Signed-off-by: Imre Deak <imre.deak at intel.com>
---
 drivers/gpu/drm/display/drm_dp_helper.c | 2 +-
 include/drm/display/drm_dp.h            | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index c488d160a3c1f..f5c596234729d 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -2602,7 +2602,7 @@ u8 drm_dp_dsc_sink_bpp_incr(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])
 {
 	u8 bpp_increment_dpcd = dsc_dpcd[DP_DSC_BITS_PER_PIXEL_INC - DP_DSC_SUPPORT];
 
-	switch (bpp_increment_dpcd) {
+	switch (bpp_increment_dpcd & DP_DSC_BITS_PER_PIXEL_MASK) {
 	case DP_DSC_BITS_PER_PIXEL_1_16:
 		return 16;
 	case DP_DSC_BITS_PER_PIXEL_1_8:
diff --git a/include/drm/display/drm_dp.h b/include/drm/display/drm_dp.h
index 784a32bfbad8f..c413ef68f9a30 100644
--- a/include/drm/display/drm_dp.h
+++ b/include/drm/display/drm_dp.h
@@ -359,6 +359,7 @@
 # define DP_DSC_BITS_PER_PIXEL_1_4          0x2
 # define DP_DSC_BITS_PER_PIXEL_1_2          0x3
 # define DP_DSC_BITS_PER_PIXEL_1_1          0x4
+# define DP_DSC_BITS_PER_PIXEL_MASK         0x7
 
 #define DP_PSR_SUPPORT                      0x070   /* XXX 1.2? */
 # define DP_PSR_IS_SUPPORTED                1
-- 
2.44.2