Re: [PATCH v2 1/2] drm/amd/display: Fall back to the native mode, not the first, on eDP/LVDS

[Alex Hung <alex.hung@amd.com>]

Reviewed-by: Alex Hung <alex.hung@amd.com>

On 10/24/26 10:33, Hugo Sales wrote:
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> 
> 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. When connector->modes has no
> preferred mode, take a mode of the native size from the list, or that
> copy if the limits pruned them all. The list comes first because
> mode_valid may have rejected the copy's timing and kept another mode of
> the same size. 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
> Signed-off-by: Hugo Sales <hugo@hsal.es>
> ---
>   .../display/amdgpu_dm/amdgpu_dm_connector.c   | 47 +++++++++++++++++++
>   1 file changed, 47 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 ded8e21897f1c..a13e3b641fd27 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)
>   {
> @@ -1545,6 +1547,51 @@ 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. Only eDP and LVDS panels
> +        * get a fallback here, since they take only their native size. On other
> +        * connectors mode_valid can also reject the preferred mode, and then
> +        * the first valid mode is the right one
> +        *
> +        * Take a mode of the native size from connector->modes if one is left,
> +        * since mode_valid may have rejected the preferred timing itself. The
> +        * probe sorts the list, so the first one has the highest refresh rate
> +        * left. If the limits pruned them all, use the copy of the preferred
> +        * mode that amdgpu_dm_get_native_mode() keeps in the encoder. It is
> +        * made on every probe, before the limits apply
> +        */
> +       if (!preferred_mode && aconnector && 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);
> +               const struct drm_display_mode *enc_native =
> +                       encoder ? &to_amdgpu_encoder(encoder)->native_mode : NULL;
> +
> +               if (enc_native && enc_native->clock) {
> +                       list_for_each_entry(connector_mode, &connector->modes, head) {
> +                               if (connector_mode->hdisplay == enc_native->hdisplay &&
> +                                   connector_mode->vdisplay == enc_native->vdisplay) {
> +                                       preferred_mode = connector_mode;
> +                                       break;
> +                               }
> +                       }
> +
> +                       /*
> +                        * saved_mode is only used for FreeSync video modes, and
> +                        * that path doesn't read preferred_mode
> +                        */
> +                       if (!preferred_mode) {
> +                               drm_mode_init(&saved_mode, enc_native);
> +                               drm_mode_set_crtcinfo(&saved_mode, CRTC_INTERLACE_HALVE_V);
> +                               preferred_mode = &saved_mode;
> +                       }
> +               }
> +       }
> +
>          if (!preferred_mode)
>                  preferred_mode = list_first_entry_or_null(
>                                  &connector->modes,
> --
> 2.55.0