[PATCH v5 0/7] DisplayID DSC passthrough timing support

[PATCH v5 0/7] DisplayID DSC passthrough timing support

[Yaroslav Bolyukin]

From: Lach <iam@lach.pw>

VESA DisplayID spec allows the device to force its DSC bits per pixel
value.

For example, the HTC Vive Pro 2 VR headset uses this value in
high-resolution modes (3680x1836@90-120, 4896x2448@90-120), and when the
kernel doesn't respect this parameter, garbage is displayed on the HMD
instead.

Me and other users have successfully tested the old (v3) version of this
patch (which was applying DSC BPP value unconditionally, thus incorrect:
https://lkml.org/lkml/2023/2/26/116) on Vive Pro 2 and
Bigscreen Beyond VR headsets, and have been using it daily, it is known
to work and doesn't seem to break anything else since 2022.

Previously, I didn't have enough dedication to get it merged, I hope
this time I will manage to get it to v6.19 :D

Regarding driver support - I have looked at amdgpu and Nvidia's
open-gpu-kernel-modules, and both seem to have some indication for this
value; however, in Linux, it is unused in both.

First patch implements parsing of DSC BPP values and display mode VII
timings flag which mandates that the DSC BPP value should actually be
used for this display mode.

The second patch implements handling of this value for AMDGPU driver.

The only thing that I don't like in the current implementation, is how
the value of `dsc_passthrough_timings_support` flag is propagated from
the connector display modes to the mode created in `DRM_IOCTL_MODE_SETCRTC`
handler (which is used for VR display initialization in Monado and
StreamVR), it feels like this flag should be initialized by the kernel
itself, but as far as I can see there is no correct way to do this, as
the timing constraints calculation belongs to the individual drivers.

Another problem with how this flag is set, is that there is no hard
connection between modes creaded in `SETCRTC` and the modes actually
defined by connector, so I implement an assumption that this flag should
be the same between choosen mode and the preferred display mode. Given
that previously due to the missing support for this flag displays
were only showing garbage, I believe this assumption won't break
anything.

Both of those downsides are due to the fact my understanding of DRM
subsystem is not that high. If another implementation would be proposed
by AMDGPU maintainers - I will gladly implement it here.

v4->v5:
 * The patch was split into multiple
 * Disabled MSO parsing for eDP displays
 * Disabled MSO logs if not used
 * Passing of type VII timings block data
 * Minor codestyle changes: lines moved around, naming
v3->v4:
 * This patch now parses timings support flag on type VII block, instead
   of applying it unconditionally. Previously I didn't understand the
   spec properly.
 * Now it also is not being applied for non-supported and/or non-VII
   blocks in amdgpu driver.

Regards,

Lach

Yaroslav Bolyukin (7):
  drm/edid: rename VESA block parsing functions to more generic name
  drm/edid: prepare for VESA vendor-specific data block extension
  drm/edid: MSO should only be used for non-eDP displays
  drm/edid: parse DSC DPP passthru support flag for mode VII timings
  drm/edid: for consistency, use mask everywhere for block rev parsing
  drm/edid: parse DRM VESA dsc bpp target
  drm/amd: use fixed dsc bits-per-pixel from edid

 .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c |  12 +++
 drivers/gpu/drm/drm_displayid_internal.h      |  11 ++
 drivers/gpu/drm/drm_edid.c                    | 101 +++++++++++-------
 include/drm/drm_connector.h                   |   6 ++
 include/drm/drm_modes.h                       |  10 ++
 5 files changed, 103 insertions(+), 37 deletions(-)

-- 
2.51.0

[PATCH v5 1/7] drm/edid: rename VESA block parsing functions to more generic name

[Yaroslav Bolyukin]

Those functions would also parse DSC Bits Per Pixel value in the future
commits.

Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>
---
 drivers/gpu/drm/drm_edid.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index e2e85345aa9a..4fcde52291ce 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -6524,8 +6524,8 @@ static void drm_get_monitor_range(struct drm_connector *connector,
 		    info->monitor_range.min_vfreq, info->monitor_range.max_vfreq);
 }
 
-static void drm_parse_vesa_mso_data(struct drm_connector *connector,
-				    const struct displayid_block *block)
+static void drm_parse_vesa_specific_block(struct drm_connector *connector,
+					  const struct displayid_block *block)
 {
 	struct displayid_vesa_vendor_specific_block *vesa =
 		(struct displayid_vesa_vendor_specific_block *)block;
@@ -6584,8 +6584,8 @@ static void drm_parse_vesa_mso_data(struct drm_connector *connector,
 		    info->mso_stream_count, info->mso_pixel_overlap);
 }
 
-static void drm_update_mso(struct drm_connector *connector,
-			   const struct drm_edid *drm_edid)
+static void drm_update_vesa_specific_block(struct drm_connector *connector,
+					   const struct drm_edid *drm_edid)
 {
 	const struct displayid_block *block;
 	struct displayid_iter iter;
@@ -6593,7 +6593,7 @@ static void drm_update_mso(struct drm_connector *connector,
 	displayid_iter_edid_begin(drm_edid, &iter);
 	displayid_iter_for_each(block, &iter) {
 		if (block->tag == DATA_BLOCK_2_VENDOR_SPECIFIC)
-			drm_parse_vesa_mso_data(connector, block);
+			drm_parse_vesa_specific_block(connector, block);
 	}
 	displayid_iter_end(&iter);
 }
@@ -6753,7 +6753,7 @@ static void update_display_info(struct drm_connector *connector,
 	if (edid->features & DRM_EDID_FEATURE_RGB_YCRCB422)
 		info->color_formats |= DRM_COLOR_FORMAT_YCBCR422;
 
-	drm_update_mso(connector, drm_edid);
+	drm_update_vesa_specific_block(connector, drm_edid);
 
 out:
 	if (drm_edid_has_internal_quirk(connector, EDID_QUIRK_NON_DESKTOP)) {
-- 
2.51.0

[PATCH v5 2/7] drm/edid: prepare for VESA vendor-specific data block extension

[Yaroslav Bolyukin]

Current VESA vendor-specific block parsing expects real block size to be
the same as the defined struct size, use real offsets in conditionals
instead to add struct fields in future commits.

Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>
---
 drivers/gpu/drm/drm_edid.c | 28 ++++++++++++----------------
 1 file changed, 12 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 4fcde52291ce..725ae5f9d160 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -6541,7 +6541,7 @@ static void drm_parse_vesa_specific_block(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,
 			    "[CONNECTOR:%d:%s] Unexpected VESA vendor block size\n",
 			    connector->base.id, connector->name);
@@ -6564,24 +6564,20 @@ static void drm_parse_vesa_specific_block(struct drm_connector *connector,
 		break;
 	}
 
-	if (!info->mso_stream_count) {
-		info->mso_pixel_overlap = 0;
-		return;
-	}
-
-	info->mso_pixel_overlap = FIELD_GET(DISPLAYID_VESA_MSO_OVERLAP, vesa->mso);
-	if (info->mso_pixel_overlap > 8) {
+	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,
+				    "[CONNECTOR:%d:%s] Reserved MSO pixel overlap value %u\n",
+				    connector->base.id, connector->name,
+				    info->mso_pixel_overlap);
+			info->mso_pixel_overlap = 8;
+		}
 		drm_dbg_kms(connector->dev,
-			    "[CONNECTOR:%d:%s] Reserved MSO pixel overlap value %u\n",
+			    "[CONNECTOR:%d:%s] MSO stream count %u, pixel overlap %u\n",
 			    connector->base.id, connector->name,
-			    info->mso_pixel_overlap);
-		info->mso_pixel_overlap = 8;
+			    info->mso_stream_count, info->mso_pixel_overlap);
 	}
-
-	drm_dbg_kms(connector->dev,
-		    "[CONNECTOR:%d:%s] MSO stream count %u, pixel overlap %u\n",
-		    connector->base.id, connector->name,
-		    info->mso_stream_count, info->mso_pixel_overlap);
 }
 
 static void drm_update_vesa_specific_block(struct drm_connector *connector,
-- 
2.51.0

[PATCH v5 3/7] drm/edid: MSO should only be used for non-eDP displays

[Yaroslav Bolyukin]

As per DisplayID v2.1a spec:
If Offset 06h[2:0] is programmed to 001b (External DisplayPort), this field shallbe cleared to 00b (Not supported).

Ref: https://lore.kernel.org/lkml/3abc1087618c822e5676e67a3ec2e64e506dc5ec@intel.com/
Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>
---
 drivers/gpu/drm/drm_displayid_internal.h |  4 +++
 drivers/gpu/drm/drm_edid.c               | 36 +++++++++++++++---------
 2 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/drm_displayid_internal.h b/drivers/gpu/drm/drm_displayid_internal.h
index 957dd0619f5c..cf02647b41b4 100644
--- a/drivers/gpu/drm/drm_displayid_internal.h
+++ b/drivers/gpu/drm/drm_displayid_internal.h
@@ -142,9 +142,13 @@ struct displayid_formula_timing_block {
 	struct displayid_formula_timings_9 timings[];
 } __packed;
 
+#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_DP_TYPE_EDP	0
+#define DISPLAYID_VESA_DP_TYPE_DP	1
+
 struct displayid_vesa_vendor_specific_block {
 	struct displayid_block base;
 	u8 oui[3];
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 725ae5f9d160..13df2854617c 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -6530,6 +6530,7 @@ static void drm_parse_vesa_specific_block(struct drm_connector *connector,
 	struct displayid_vesa_vendor_specific_block *vesa =
 		(struct displayid_vesa_vendor_specific_block *)block;
 	struct drm_display_info *info = &connector->display_info;
+	int dp_type;
 
 	if (block->num_bytes < 3) {
 		drm_dbg_kms(connector->dev,
@@ -6548,20 +6549,29 @@ static void drm_parse_vesa_specific_block(struct drm_connector *connector,
 		return;
 	}
 
-	switch (FIELD_GET(DISPLAYID_VESA_MSO_MODE, vesa->mso)) {
-	default:
-		drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] Reserved MSO mode value\n",
+	dp_type = FIELD_GET(DISPLAYID_VESA_DP_TYPE, vesa->data_structure_type);
+	if (dp_type > 1) {
+		drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] Reserved dp type value\n",
 			    connector->base.id, connector->name);
-		fallthrough;
-	case 0:
-		info->mso_stream_count = 0;
-		break;
-	case 1:
-		info->mso_stream_count = 2; /* 2 or 4 links */
-		break;
-	case 2:
-		info->mso_stream_count = 4; /* 4 links */
-		break;
+	}
+
+	/* MSO is not supported for eDP */
+	if (dp_type != DISPLAYID_VESA_DP_TYPE_EDP) {
+		switch (FIELD_GET(DISPLAYID_VESA_MSO_MODE, vesa->mso)) {
+		default:
+			drm_dbg_kms(connector->dev, "[CONNECTOR:%d:%s] Reserved MSO mode value\n",
+				    connector->base.id, connector->name);
+			fallthrough;
+		case 0:
+			info->mso_stream_count = 0;
+			break;
+		case 1:
+			info->mso_stream_count = 2; /* 2 or 4 links */
+			break;
+		case 2:
+			info->mso_stream_count = 4; /* 4 links */
+			break;
+		}
 	}
 
 	if (info->mso_stream_count) {
-- 
2.51.0

[PATCH v5 4/7] drm/edid: parse DSC DPP passthru support flag for mode VII timings

[Yaroslav Bolyukin]

Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>
---
 drivers/gpu/drm/drm_displayid_internal.h |  2 ++
 drivers/gpu/drm/drm_edid.c               | 12 ++++++++----
 include/drm/drm_modes.h                  | 10 ++++++++++
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_displayid_internal.h b/drivers/gpu/drm/drm_displayid_internal.h
index cf02647b41b4..8ea20b1c6921 100644
--- a/drivers/gpu/drm/drm_displayid_internal.h
+++ b/drivers/gpu/drm/drm_displayid_internal.h
@@ -97,6 +97,7 @@ struct displayid_header {
 	u8 ext_count;
 } __packed;
 
+#define DISPLAYID_BLOCK_REV	GENMASK(2, 0)
 struct displayid_block {
 	u8 tag;
 	u8 rev;
@@ -125,6 +126,7 @@ struct displayid_detailed_timings_1 {
 	__le16 vsw;
 } __packed;
 
+#define DISPLAYID_BLOCK_PASSTHROUGH_TIMINGS_SUPPORT	BIT(3)
 struct displayid_detailed_timing_block {
 	struct displayid_block base;
 	struct displayid_detailed_timings_1 timings[];
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index 13df2854617c..a1dc4331c4cb 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -6789,8 +6789,8 @@ static void update_display_info(struct drm_connector *connector,
 }
 
 static struct drm_display_mode *drm_mode_displayid_detailed(struct drm_device *dev,
-							    const struct displayid_detailed_timings_1 *timings,
-							    bool type_7)
+							    const struct displayid_block *block,
+							    const struct displayid_detailed_timings_1 *timings)
 {
 	struct drm_display_mode *mode;
 	unsigned int pixel_clock = (timings->pixel_clock[0] |
@@ -6806,11 +6806,16 @@ static struct drm_display_mode *drm_mode_displayid_detailed(struct drm_device *d
 	unsigned int vsync_width = le16_to_cpu(timings->vsw) + 1;
 	bool hsync_positive = le16_to_cpu(timings->hsync) & (1 << 15);
 	bool vsync_positive = le16_to_cpu(timings->vsync) & (1 << 15);
+	bool type_7 = block->tag == DATA_BLOCK_2_TYPE_7_DETAILED_TIMING;
 
 	mode = drm_mode_create(dev);
 	if (!mode)
 		return NULL;
 
+	if (type_7 && FIELD_GET(DISPLAYID_BLOCK_REV, block->rev) >= 1)
+		mode->dsc_passthrough_timings_support =
+			!!(block->rev & DISPLAYID_BLOCK_PASSTHROUGH_TIMINGS_SUPPORT);
+
 	/* resolution is kHz for type VII, and 10 kHz for type I */
 	mode->clock = type_7 ? pixel_clock : pixel_clock * 10;
 	mode->hdisplay = hactive;
@@ -6843,7 +6848,6 @@ static int add_displayid_detailed_1_modes(struct drm_connector *connector,
 	int num_timings;
 	struct drm_display_mode *newmode;
 	int num_modes = 0;
-	bool type_7 = block->tag == DATA_BLOCK_2_TYPE_7_DETAILED_TIMING;
 	/* blocks must be multiple of 20 bytes length */
 	if (block->num_bytes % 20)
 		return 0;
@@ -6852,7 +6856,7 @@ static int add_displayid_detailed_1_modes(struct drm_connector *connector,
 	for (i = 0; i < num_timings; i++) {
 		struct displayid_detailed_timings_1 *timings = &det->timings[i];
 
-		newmode = drm_mode_displayid_detailed(connector->dev, timings, type_7);
+		newmode = drm_mode_displayid_detailed(connector->dev, block, timings);
 		if (!newmode)
 			continue;
 
diff --git a/include/drm/drm_modes.h b/include/drm/drm_modes.h
index b9bb92e4b029..312e5c03af9a 100644
--- a/include/drm/drm_modes.h
+++ b/include/drm/drm_modes.h
@@ -417,6 +417,16 @@ struct drm_display_mode {
 	 */
 	enum hdmi_picture_aspect picture_aspect_ratio;
 
+	/**
+	 * @dsc_passthrough_timing_support:
+	 *
+	 * Indicates whether this mode timing descriptor is supported
+	 * with specific target DSC bits per pixel only.
+	 *
+	 * VESA vendor-specific data block shall exist with the relevant
+	 * DSC bits per pixel declaration when this flag is set to true.
+	 */
+	bool dsc_passthrough_timings_support;
 };
 
 /**
-- 
2.51.0

[PATCH v5 5/7] drm/edid: for consistency, use mask everywhere for block rev parsing

[Yaroslav Bolyukin]

Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>
---
 drivers/gpu/drm/drm_displayid_internal.h | 1 +
 drivers/gpu/drm/drm_edid.c               | 3 ++-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_displayid_internal.h b/drivers/gpu/drm/drm_displayid_internal.h
index 8ea20b1c6921..38f9d628e2d6 100644
--- a/drivers/gpu/drm/drm_displayid_internal.h
+++ b/drivers/gpu/drm/drm_displayid_internal.h
@@ -139,6 +139,7 @@ struct displayid_formula_timings_9 {
 	u8 vrefresh;
 } __packed;
 
+#define DISPLAYID_BLOCK_DESCRIPTOR_PAYLOAD_BYTES	GENMASK(6, 4)
 struct displayid_formula_timing_block {
 	struct displayid_block base;
 	struct displayid_formula_timings_9 timings[];
diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
index a1dc4331c4cb..4fa39989e446 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -6903,7 +6903,8 @@ static int add_displayid_formula_modes(struct drm_connector *connector,
 	struct drm_display_mode *newmode;
 	int num_modes = 0;
 	bool type_10 = block->tag == DATA_BLOCK_2_TYPE_10_FORMULA_TIMING;
-	int timing_size = 6 + ((formula_block->base.rev & 0x70) >> 4);
+	int timing_size = 6 +
+		FIELD_GET(DISPLAYID_BLOCK_DESCRIPTOR_PAYLOAD_BYTES, formula_block->base.rev);
 
 	/* extended blocks are not supported yet */
 	if (timing_size != 6)
-- 
2.51.0

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

[Yaroslav Bolyukin]

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>
---
 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

[PATCH v5 7/7] drm/amd: use fixed dsc bits-per-pixel from edid

[Yaroslav Bolyukin]

VESA vendor header from DisplayID spec may contain fixed bit per pixel
rate, it should be used by drm driver for the modes that declare
they are only supported with the declared fixed bits per pixel value.

It is however unclear how to deal with the modes created from userspace.
Current implementation assumes that fixed bits per pixel value should
always be used if the preferred display mode has this flag set, which is
the case for all the known hardware.

Signed-off-by: Yaroslav Bolyukin <iam@lach.pw>
---
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 0d03e324d5b9..739d5dabcf41 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -6521,6 +6521,11 @@ static void fill_stream_properties_from_drm_display_mode(
 
 	stream->output_color_space = get_output_color_space(timing_out, connector_state);
 	stream->content_type = get_output_content_type(connector_state);
+
+	/* DisplayID Type VII pass-through timings. */
+	if (mode_in->dsc_passthrough_timings_support && info->dp_dsc_bpp_x16 != 0) {
+		stream->timing.dsc_fixed_bits_per_pixel_x16 = info->dp_dsc_bpp_x16;
+	}
 }
 
 static void fill_audio_info(struct audio_info *audio_info,
@@ -7067,6 +7072,13 @@ create_stream_for_sink(struct drm_connector *connector,
 					&mode, preferred_mode, scale);
 
 			preferred_refresh = drm_mode_vrefresh(preferred_mode);
+
+			/*
+			 * HACK: In case of multiple supported modes, we should look at the matching mode to decide this flag.
+			 * But what is matching mode, how should it be decided?
+			 * Assuming that only preferred mode would have this flag.
+			 */
+			mode.dsc_passthrough_timings_support = preferred_mode->dsc_passthrough_timings_support;
 		}
 	}
 
-- 
2.51.0