Re: [PATCH 1/2] drm/amd/display: Fall back to the native mode, not the first, on eDP/LVDS

[Chung, ChiaHsuan (Tom)]

On 10/15/2026 6:30 AM, Hugo Sales wrote:
> Currently, create_stream_for_sink() takes the native timing for a scaled
> mode from the preferred mode in connector->modes. After fbdev emulation
> probes with size limits below the native resolution, as it does when
> video= sets a smaller mode, that mode is no longer in the list
>
> If that probe is the last one before a suspend, for example after an
> HDMI hotplug, the resume finds no preferred mode, and the panel is
> driven with the scaled mode's timing instead of its own
>
> amdgpu_dm_get_native_mode() copies the preferred mode to the encoder on
> every probe, before the size limits apply. Fall back to that copy when
> connector->modes has no preferred mode. Limit this to eDP and LVDS,
> where amdgpu turns scaling on by itself. On other connectors mode_valid
> can also leave the preferred mode out, and then the first valid mode is
> the right fallback
>
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/5983
> Assisted-by: Claude:claude-opus-5-5
> Signed-off-by: Hugo Sales <hugo@xxxxxxx>

Hi Hugo,

Thanks for the patch and the detailed analysis.
This no longer applies to the current amd-staging-drm-next. It
conflicts with commit 3299935e65c0 ("drm/amd/display: Use separate
iterator for preferred mode lookup"), which landed after the tree you
based this on. That commit removed native_mode_found from
create_stream_for_sink() and now checks preferred_mode directly:

    if (!preferred_mode)
        preferred_mode = list_first_entry_or_null(...);

Could you rebase the series onto the latest amd-staging-drm-next and
send a v2? The change should be mechanical: test !preferred_mode
instead of !native_mode_found, and drop the native_mode_found = true
assignment. The logic stays the same. Patch 2/2 still applies cleanly.
Also, the dm_test_fs_caps_hdmi_vsdb and dm_test_fs_caps_pcon_whitelist
failures you mentioned in the cover letter were fixed by commit
5ac0b4dd2a1f ("drm/amd/display: Fix FreeSync caps tests after common
EDID VSDB switch"). With the series rebased that way, the whole
amdgpu_dm_connector KUnit suite passes on our side, including your new
tests.


Thanks,
Tom

> ---
>   .../display/amdgpu_dm/amdgpu_dm_connector.c   | 28 +++++++++++++++++++
>   1 file changed, 28 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c
> index 428a5f937..a1dc3e287 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_connector.c
> @@ -257,6 +257,8 @@ STATIC_IFN_KUNIT void update_subconnector_property(struct amdgpu_dm_connector *a
>   EXPORT_IF_KUNIT(update_subconnector_property);
>
>   STATIC_IFN_KUNIT int amdgpu_dm_connector_get_modes(struct drm_connector *connector);
> +STATIC_IFN_KUNIT struct drm_encoder *amdgpu_dm_connector_to_encoder(
> +       struct drm_connector *connector);
>
>   STATIC_IFN_KUNIT void amdgpu_dm_fbc_init(struct drm_connector *connector)
>   {
> @@ -1470,6 +1472,7 @@ create_stream_for_sink(struct drm_connector *connector,
>          struct dc_stream_state *stream = NULL;
>          struct drm_display_mode mode;
>          struct drm_display_mode saved_mode;
> +       struct drm_display_mode native_mode;
>          struct drm_display_mode *freesync_mode = NULL;
>          bool native_mode_found = false;
>          bool recalculate_timing = false;
> @@ -1529,6 +1532,31 @@ create_stream_for_sink(struct drm_connector *connector,
>                          break;
>                  }
>          }
> +
> +       /*
> +        * After a probe with size limits smaller than the preferred mode,
> +        * connector->modes no longer has that mode, and the first mode left
> +        * would become the stream timing. fbdev emulation probes with limits
> +        * that video= can set below the native size. The encoder has a copy of
> +        * the preferred mode from amdgpu_dm_get_native_mode(), made on every
> +        * probe before the limits apply, so use that copy. Only do this for eDP
> +        * and LVDS panels, which take only their native timing. On other
> +        * connectors mode_valid can also reject the preferred mode, and then
> +        * the first valid mode is the right one
> +        */
> +       if (!native_mode_found && aconnector && !aconnector->mst_root && aconnector->drm_edid &&
> +           (connector->connector_type == DRM_MODE_CONNECTOR_eDP ||
> +            connector->connector_type == DRM_MODE_CONNECTOR_LVDS)) {
> +               struct drm_encoder *encoder = amdgpu_dm_connector_to_encoder(connector);
> +
> +               if (encoder && to_amdgpu_encoder(encoder)->native_mode.clock) {
> +                       drm_mode_copy(&native_mode, &to_amdgpu_encoder(encoder)->native_mode);
> +                       drm_mode_set_crtcinfo(&native_mode, CRTC_INTERLACE_HALVE_V);
> +                       preferred_mode = &native_mode;
> +                       native_mode_found = true;
> +               }
> +       }
> +
>          if (!native_mode_found)
>                  preferred_mode = list_first_entry_or_null(
>                                  &connector->modes,
> --
> 2.55.0