drm/edid: Refactor HFVSDB parsing for DSC1.2

DSC capabilities are given in bytes 11-13 of VSDB (i.e. bytes 8-10 of
SCDS). Since minimum length of Data block is 7, all bytes greater than 7
must be read only after checking the length of the data block.

This patch adds check for data block length before reading relavant DSC
bytes.
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220916100551.2531750-4-ankit.k.nautiyal@intel.com

drivers/gpu/drm/drm_edid.c

@@ -5755,9 +5755,6 @@ static void drm_parse_ycbcr420_deep_color_info(struct drm_connector *connector,
 static void drm_parse_dsc_info(struct drm_hdmi_dsc_cap *hdmi_dsc,
 			       const u8 *hf_scds)
 {
-	u8 dsc_max_slices;
-	u8 dsc_max_frl_rate;
-
 	hdmi_dsc->v_1p2 = hf_scds[11] & DRM_EDID_DSC_1P2;
 
 	if (!hdmi_dsc->v_1p2)
@@ -5776,47 +5773,54 @@ static void drm_parse_dsc_info(struct drm_hdmi_dsc_cap *hdmi_dsc,
 		/* Supports min 8 BPC if DSC 1.2 is supported*/
 		hdmi_dsc->bpc_supported = 8;
 
-	dsc_max_frl_rate = (hf_scds[12] & DRM_EDID_DSC_MAX_FRL_RATE_MASK) >> 4;
-	drm_get_max_frl_rate(dsc_max_frl_rate, &hdmi_dsc->max_lanes,
-			     &hdmi_dsc->max_frl_rate_per_lane);
-	hdmi_dsc->total_chunk_kbytes = hf_scds[13] & DRM_EDID_DSC_TOTAL_CHUNK_KBYTES;
+	if (cea_db_payload_len(hf_scds) >= 12 && hf_scds[12]) {
+		u8 dsc_max_slices;
+		u8 dsc_max_frl_rate;
 
-	dsc_max_slices = hf_scds[12] & DRM_EDID_DSC_MAX_SLICES;
+		dsc_max_frl_rate = (hf_scds[12] & DRM_EDID_DSC_MAX_FRL_RATE_MASK) >> 4;
+		drm_get_max_frl_rate(dsc_max_frl_rate, &hdmi_dsc->max_lanes,
+				     &hdmi_dsc->max_frl_rate_per_lane);
 
-	switch (dsc_max_slices) {
-	case 1:
-		hdmi_dsc->max_slices = 1;
-		hdmi_dsc->clk_per_slice = 340;
-		break;
-	case 2:
-		hdmi_dsc->max_slices = 2;
-		hdmi_dsc->clk_per_slice = 340;
-		break;
-	case 3:
-		hdmi_dsc->max_slices = 4;
-		hdmi_dsc->clk_per_slice = 340;
-		break;
-	case 4:
-		hdmi_dsc->max_slices = 8;
-		hdmi_dsc->clk_per_slice = 340;
-		break;
-	case 5:
-		hdmi_dsc->max_slices = 8;
-		hdmi_dsc->clk_per_slice = 400;
-		break;
-	case 6:
-		hdmi_dsc->max_slices = 12;
-		hdmi_dsc->clk_per_slice = 400;
-		break;
-	case 7:
-		hdmi_dsc->max_slices = 16;
-		hdmi_dsc->clk_per_slice = 400;
-		break;
-	case 0:
-	default:
-		hdmi_dsc->max_slices = 0;
-		hdmi_dsc->clk_per_slice = 0;
+		dsc_max_slices = hf_scds[12] & DRM_EDID_DSC_MAX_SLICES;
+
+		switch (dsc_max_slices) {
+		case 1:
+			hdmi_dsc->max_slices = 1;
+			hdmi_dsc->clk_per_slice = 340;
+			break;
+		case 2:
+			hdmi_dsc->max_slices = 2;
+			hdmi_dsc->clk_per_slice = 340;
+			break;
+		case 3:
+			hdmi_dsc->max_slices = 4;
+			hdmi_dsc->clk_per_slice = 340;
+			break;
+		case 4:
+			hdmi_dsc->max_slices = 8;
+			hdmi_dsc->clk_per_slice = 340;
+			break;
+		case 5:
+			hdmi_dsc->max_slices = 8;
+			hdmi_dsc->clk_per_slice = 400;
+			break;
+		case 6:
+			hdmi_dsc->max_slices = 12;
+			hdmi_dsc->clk_per_slice = 400;
+			break;
+		case 7:
+			hdmi_dsc->max_slices = 16;
+			hdmi_dsc->clk_per_slice = 400;
+			break;
+		case 0:
+		default:
+			hdmi_dsc->max_slices = 0;
+			hdmi_dsc->clk_per_slice = 0;
+		}
 	}
+
+	if (cea_db_payload_len(hf_scds) >= 13 && hf_scds[13])
+		hdmi_dsc->total_chunk_kbytes = hf_scds[13] & DRM_EDID_DSC_TOTAL_CHUNK_KBYTES;
 }
 
 /* Sink Capability Data Structure */
@@ -5825,6 +5829,7 @@ static void drm_parse_hdmi_forum_scds(struct drm_connector *connector,
 {
 	struct drm_display_info *display = &connector->display_info;
 	struct drm_hdmi_info *hdmi = &display->hdmi;
+	struct drm_hdmi_dsc_cap *hdmi_dsc = &hdmi->dsc_cap;
 
 	display->has_hdmi_infoframe = true;
 
@@ -5865,17 +5870,17 @@ static void drm_parse_hdmi_forum_scds(struct drm_connector *connector,
 
 	if (hf_scds[7]) {
 		u8 max_frl_rate;
-		struct drm_hdmi_dsc_cap *hdmi_dsc = &hdmi->dsc_cap;
 
 		DRM_DEBUG_KMS("hdmi_21 sink detected. parsing edid\n");
 		max_frl_rate = (hf_scds[7] & DRM_EDID_MAX_FRL_RATE_MASK) >> 4;
 		drm_get_max_frl_rate(max_frl_rate, &hdmi->max_lanes,
 				     &hdmi->max_frl_rate_per_lane);
-
-		drm_parse_dsc_info(hdmi_dsc, hf_scds);
 	}
 
 	drm_parse_ycbcr420_deep_color_info(connector, hf_scds);
+
+	if (cea_db_payload_len(hf_scds) >= 11 && hf_scds[11])
+		drm_parse_dsc_info(hdmi_dsc, hf_scds);
 }
 
 static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,