drm/dsc: Modify DRM helper to return complete DSC color depth capabilities

DSC DPCD color depth register advertises its color depth capabilities
by setting each of the bits that corresponding to a specific color
depth. This patch defines those specific color depths and adds
a helper to return an array of color depth capabilities.

v2:
* Simplify the logic (Ville)
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Acked-by: Sean Paul <seanpaul@chromium.org> (For merging through
drm-intel)
Reviewed-by: Ville Syrjala <ville.syrjala@linux.intel.com>
Reviewed-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181127214125.17658-1-manasi.d.navare@intel.com

drivers/gpu/drm/drm_dp_helper.c

@@ -1428,17 +1428,19 @@ u8 drm_dp_dsc_sink_line_buf_depth(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])
 }
 EXPORT_SYMBOL(drm_dp_dsc_sink_line_buf_depth);
 
-u8 drm_dp_dsc_sink_max_color_depth(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])
+int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE],
+					 u8 dsc_bpc[3])
 {
+	int num_bpc = 0;
 	u8 color_depth = dsc_dpcd[DP_DSC_DEC_COLOR_DEPTH_CAP - DP_DSC_SUPPORT];
 
 	if (color_depth & DP_DSC_12_BPC)
-		return 12;
+		dsc_bpc[num_bpc++] = 12;
 	if (color_depth & DP_DSC_10_BPC)
-		return 10;
+		dsc_bpc[num_bpc++] = 10;
 	if (color_depth & DP_DSC_8_BPC)
-		return 8;
+		dsc_bpc[num_bpc++] = 8;
 
-	return 0;
+	return num_bpc;
 }
-EXPORT_SYMBOL(drm_dp_dsc_sink_max_color_depth);
+EXPORT_SYMBOL(drm_dp_dsc_sink_supported_input_bpcs);

include/drm/drm_dp_helper.h

@@ -1123,7 +1123,8 @@ drm_dp_is_branch(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
 u8 drm_dp_dsc_sink_max_slice_count(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE],
 				   bool is_edp);
 u8 drm_dp_dsc_sink_line_buf_depth(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE]);
-u8 drm_dp_dsc_sink_max_color_depth(const u8 dsc_dpc[DP_DSC_RECEIVER_CAP_SIZE]);
+int drm_dp_dsc_sink_supported_input_bpcs(const u8 dsc_dpc[DP_DSC_RECEIVER_CAP_SIZE],
+					 u8 dsc_bpc[3]);
 
 static inline bool
 drm_dp_sink_supports_dsc(const u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE])