Re: [PATCH v6 3/7] drm/edid: MSO should only be used for non-eDP displays

[Yaroslav]

On 2025-11-26 15:10, Jani Nikula wrote:
On Wed, 26 Nov 2025, Yaroslav Bolyukin <i...@lach.pw> wrote:
As per DisplayID v2.1a spec:
If Offset 06h[2:0] is programmed to 001b (External DisplayPort), this
field shall be cleared to 00b (Not supported).

Link: 
https://lore.kernel.org/lkml/3abc1087618c822e5676e67a3ec2e64e506dc...@intel.com/
Signed-off-by: Yaroslav Bolyukin <i...@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 5b1b32f73516..72f107ae832f 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 a52fd6de9327..348aa31aea1b 100644
--- a/drivers/gpu/drm/drm_edid.c
+++ b/drivers/gpu/drm/drm_edid.c
@@ -6533,6 +6533,7 @@ 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,
@@ -6551,20 +6552,29 @@ 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) {

MSO is *only* supported on eDP, not the other way round!

BR,
Jani.


Oh, yes. For some reason I thought that MSO == MST, and it made no sense 
for me why would MST be only supported on eDP, I see now that this is a 
separate thing. I should probably don't include this patch in the 
patchset, since this is the only part that I don't have hardware to test

+               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) {