drm/edid: parse DRM VESA dsc bpp target

As per DisplayID v2.1a spec "DSC pass-through timing support",
VESA vendor-specific data block may contain target DSC bits per pixel
fields, that should be always used for the VII modes that declare they
only support working with this value (Pass-through Timing Support for
Target DSC Bits per Pixel).

Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>

fixup parse DRM vesa dsc bpp target

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

Author: CertainLach

drivers/gpu/drm/drm_displayid_internal.h

@@ -148,6 +148,8 @@ struct displayid_formula_timing_block {
 #define DISPLAYID_VESA_DP_TYPE		GENMASK(2, 0)
 #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)
 
 #define DISPLAYID_VESA_DP_TYPE_EDP	0
 #define DISPLAYID_VESA_DP_TYPE_DP	1
@@ -157,6 +159,8 @@ struct displayid_vesa_vendor_specific_block {
 	u8 oui[3];
 	u8 data_structure_type;
 	u8 mso;
+	u8 dsc_bpp_int;
+	u8 dsc_bpp_fract;
 } __packed;
 
 /*

drivers/gpu/drm/drm_edid.c

@@ -45,6 +45,7 @@
 #include <drm/drm_edid.h>
 #include <drm/drm_eld.h>
 #include <drm/drm_encoder.h>
+#include <drm/drm_fixed.h>
 #include <drm/drm_print.h>
 
 #include "drm_crtc_internal.h"
@@ -6593,6 +6594,21 @@ static void drm_parse_vesa_specific_block(struct drm_connector *connector,
 	} else {
 		info->mso_pixel_overlap = 0;
 	}
+
+	if (block->num_bytes < 7) {
+		/* DSC bpp is optional */
+		return;
+	}
+
+	info->dp_dsc_bpp_x16 = FIELD_GET(DISPLAYID_VESA_DSC_BPP_INT, vesa->dsc_bpp_int) << 4 |
+			       FIELD_GET(DISPLAYID_VESA_DSC_BPP_FRACT, vesa->dsc_bpp_fract);
+
+	if (info->dp_dsc_bpp_x16 > 0) {
+		drm_dbg_kms(connector->dev,
+			    "[CONNECTOR:%d:%s] DSC bits per pixel " FXP_Q4_FMT "\n",
+			    connector->base.id, connector->name,
+			    FXP_Q4_ARGS(info->dp_dsc_bpp_x16));
+	}
 }
 
 static void drm_update_vesa_specific_block(struct drm_connector *connector,
@@ -6641,6 +6657,7 @@ static void drm_reset_display_info(struct drm_connector *connector)
 	info->mso_stream_count = 0;
 	info->mso_pixel_overlap = 0;
 	info->max_dsc_bpp = 0;
+	info->dp_dsc_bpp_x16 = 0;
 
 	kfree(info->vics);
 	info->vics = NULL;

include/drm/drm_connector.h

@@ -837,6 +837,12 @@ struct drm_display_info {
 	 */
 	u32 max_dsc_bpp;
 
+	/**
+	 * @dp_dsc_bpp: DP Display-Stream-Compression (DSC) timing's target
+	 * DSC bits per pixel in 6.4 fixed point format. 0 means undefined.
+	 */
+	u16 dp_dsc_bpp_x16;
+
 	/**
 	 * @vics: Array of vics_len VICs. Internal to EDID parsing.
 	 */