[PATCH v2 1/2] drm/edid: parse DRM VESA dsc bpp target

[Yaroslav Bolyukin <iam@lach.pw>]

As per DisplayID v2.0 Errata E9 spec "DSC pass-through timing support"
VESA vendor-specific data block may contain target DSC bits per pixel
fields

Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>
---
 drivers/gpu/drm/drm_edid.c  | 33 ++++++++++++++++++++++-----------
 include/drm/drm_connector.h |  6 ++++++
 include/drm/drm_displayid.h |  4 ++++
 3 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index a7663f9a1..ee8c2b911 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -5270,7 +5270,7 @@ static void drm_parse_vesa_mso_data(struct drm_connector *connector,
 	if (oui(vesa->oui[0], vesa->oui[1], vesa->oui[2]) != VESA_IEEE_OUI)
 		return;
 
-	if (sizeof(*vesa) != sizeof(*block) + block->num_bytes) {
+	if (block->num_bytes < 5) {
 		drm_dbg_kms(connector->dev, "Unexpected VESA vendor block size\n");
 		return;
 	}
@@ -5290,20 +5290,29 @@ static void drm_parse_vesa_mso_data(struct drm_connector *connector,
 		break;
 	}
 
-	if (!info->mso_stream_count) {
-		info->mso_pixel_overlap = 0;
-		return;
+	info->mso_pixel_overlap = 0;
+
+	if (info->mso_stream_count) {
+		info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP, vesa->mso);
+		if (info->mso_pixel_overlap > 8) {
+			drm_dbg_kms(connector->dev, "Reserved MSO pixel overlap value %u\n",
+				info->mso_pixel_overlap);
+			info->mso_pixel_overlap = 8;
+		}
+
+		drm_dbg_kms(connector->dev, "MSO stream count %u, pixel overlap %u\n",
+			info->mso_stream_count, info->mso_pixel_overlap);
 	}
 
-	info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP, vesa->mso);
-	if (info->mso_pixel_overlap > 8) {
-		drm_dbg_kms(connector->dev, "Reserved MSO pixel overlap value %u\n",
-			    info->mso_pixel_overlap);
-		info->mso_pixel_overlap = 8;
+	if (block->num_bytes < 7) {
+		/* DSC bpp is optional */
+		return;
 	}
 
-	drm_dbg_kms(connector->dev, "MSO stream count %u, pixel overlap %u\n",
-		    info->mso_stream_count, info->mso_pixel_overlap);
+	info->dp_dsc_bpp = FIELD_GET(DISPLAYID_VESA_DSC_BPP_INT, vesa->dsc_bpp_int) * 16 +
+		FIELD_GET(DISPLAYID_VESA_DSC_BPP_FRACT, vesa->dsc_bpp_fract);
+
+	drm_dbg_kms(connector->dev, "DSC bits per pixel %u\n", info->dp_dsc_bpp);
 }
 
 static void drm_update_mso(struct drm_connector *connector, const struct edid *edid)
@@ -5348,6 +5357,8 @@ drm_reset_display_info(struct drm_connector *connector)
 
 	info->mso_stream_count = 0;
 	info->mso_pixel_overlap = 0;
+
+	info->dp_dsc_bpp = 0;
 }
 
 u32 drm_add_display_info(struct drm_connector *connector, const struct edid *edid)
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 5e36eb3df..04ef0e995 100644
--- a/include/drm/drm_connector.h
+++ b/include/drm/drm_connector.h
@@ -634,6 +634,12 @@ struct drm_display_info {
 	 * @mso_pixel_overlap: eDP MSO segment pixel overlap, 0-8 pixels.
 	 */
 	u8 mso_pixel_overlap;
+
+	/**
+	 * @dp_dsc_bpp: DP Display-Stream-Compression (DSC) timing's target
+	 * DST bits per pixel in 6.4 fixed point format. 0 means undefined
+	 */
+	u16 dp_dsc_bpp;
 };
 
 int drm_display_info_set_bus_formats(struct drm_display_info *info,
diff --git a/include/drm/drm_displayid.h b/include/drm/drm_displayid.h
index 7ffbd9f7b..1be6deddc 100644
--- a/include/drm/drm_displayid.h
+++ b/include/drm/drm_displayid.h
@@ -131,12 +131,16 @@ struct displayid_detailed_timing_block {
 
 #define DISPLAYID_VESA_MSO_OVERLAP	GENMASK(3, 0)
 #define DISPLAYID_VESA_MSO_MODE		GENMASK(6, 5)
+#define DISPLAYID_VESA_DSC_BPP_INT	GENMASK(5, 0)
+#define DISPLAYID_VESA_DSC_BPP_FRACT GENMASK(3, 0)
 
 struct displayid_vesa_vendor_specific_block {
 	struct displayid_block base;
 	u8 oui[3];
 	u8 data_structure_type;
 	u8 mso;
+	u8 dsc_bpp_int;
+	u8 dsc_bpp_fract;
 } __packed;
 
 /* DisplayID iteration */

base-commit: 1528038385c0a706aac9ac165eeb24044fef6825
-- 
2.35.1