linux-kernel - [PATCH v5 6/7] drm/edid: parse DRM VESA dsc bpp target

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Message-ID: <20251017162736.45368-7-iam@lach.pw>
Date: Fri, 17 Oct 2025 18:27:35 +0200
From: Yaroslav Bolyukin <iam@...h.pw>
To: Ville Syrjälä <ville.syrjala@...ux.intel.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Simona Vetter <simona@...ll.ch>
Cc: Harry Wentland <harry.wentland@....com>,
	Leo Li <sunpeng.li@....com>,
	Rodrigo Siqueira <siqueira@...lia.com>,
	Alex Deucher <alexander.deucher@....com>,
	Christian König <christian.koenig@....com>,
	Wayne Lin <Wayne.Lin@....com>,
	amd-gfx@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org,
	Yaroslav Bolyukin <iam@...h.pw>
Subject: [PATCH v5 6/7] 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@...h.pw>
---
 drivers/gpu/drm/drm_displayid_internal.h |  4 ++++
 drivers/gpu/drm/drm_edid.c               | 16 ++++++++++++++++
 include/drm/drm_connector.h              |  6 ++++++
 3 files changed, 26 insertions(+)

diff --git a/drivers/gpu/drm/drm_displayid_internal.h b/drivers/gpu/drm/drm_displayid_internal.h
index 38f9d628e2d6..7246ffdcd908 100644
--- a/drivers/gpu/drm/drm_displayid_internal.h
+++ b/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;
 
 /*
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 4fa39989e446..1c51158fa3a3 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -6588,6 +6588,21 @@ static void drm_parse_vesa_specific_block(struct drm_connector *connector,
 			    connector->base.id, connector->name,
 			    info->mso_stream_count, info->mso_pixel_overlap);
 	}
+
+	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 x16 %u\n",
+			    connector->base.id, connector->name,
+			    info->dp_dsc_bpp_x16);
+	}
 }
 
 static void drm_update_vesa_specific_block(struct drm_connector *connector,
@@ -6636,6 +6651,7 @@ 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;
diff --git a/include/drm/drm_connector.h b/include/drm/drm_connector.h
index 8f34f4b8183d..7decfc288aa3 100644
--- a/include/drm/drm_connector.h
+++ b/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.
 	 */
-- 
2.51.0