drm/amd/display: Mask DPCD field to avoid reading unsupported field value

[Why]
DSC will be disabled if DPCD 0006F[6:3] is set to a non-zero value
because bits 6:3 are not currently supported. When 6:3 is populated, an
unsupported INCREMENT OF bits_per_pixel value is read (DPCD 0006F[2:0])

[How]
Mask the INCREMENT OF bits_per_pixel field so that values in the
unsupported field are ignored.
Signed-off-by: Jaehyun Chung <jaehyun.chung@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dsc/dc_dsc.c

@@ -192,8 +192,10 @@ static bool dsc_throughput_from_dpcd(int dpcd_throughput, int *throughput)
 }
 
 
-static bool dsc_bpp_increment_div_from_dpcd(int bpp_increment_dpcd, uint32_t *bpp_increment_div)
+static bool dsc_bpp_increment_div_from_dpcd(uint8_t bpp_increment_dpcd, uint32_t *bpp_increment_div)
 {
+	// Mask bpp increment dpcd field to avoid reading other fields
+	bpp_increment_dpcd &= 0x7;
 
 	switch (bpp_increment_dpcd) {
 	case 0: