Re: [RFC PATCH v2 1/5] drm/msm/dp: fix panel bridge attachment

[Stephen Boyd <swboyd@chromium.org>]

Quoting Dmitry Baryshkov (2022-02-11 14:40:02)
> In commit 8a3b4c17f863 ("drm/msm/dp: employ bridge mechanism for display
> enable and disable") the DP driver received a drm_bridge instance, which
> is always attached to the encoder as a root bridge. However it conflicts
> with the panel_bridge support for eDP panels. The panel bridge attaches
> to the encoder before the "dp" bridge has a chace to do so. Change

s/chace/chance/

> panel_bridge attachment to come after dp_bridge attachment.

s/panel_bridge/panel bridge/ possibly? And maybe clarify that dp_bridge
is the "DP driver's drm_bridge instance created in
msm_dp_bridge_init()"?

My understanding is that we want to pass the bridge created in
msm_dp_bridge_init() as the 'previous' bridge so that it attaches the
panel bridge to the output of the DP bridge that's attached to the
encoder.

>
> Fixes: 8a3b4c17f863 ("drm/msm/dp: employ bridge mechanism for display enable and disable")
> Cc: Kuogee Hsieh <quic_khsieh@quicinc.com>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> ---

Reviewed-by: Stephen Boyd <swboyd@chromium.org>

>  drivers/gpu/drm/msm/dp/dp_drm.c | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_drm.c b/drivers/gpu/drm/msm/dp/dp_drm.c
> index d4d360d19eba..26ef41a4c1b6 100644
> --- a/drivers/gpu/drm/msm/dp/dp_drm.c
> +++ b/drivers/gpu/drm/msm/dp/dp_drm.c
> @@ -169,16 +169,6 @@ struct drm_connector *dp_drm_connector_init(struct msm_dp *dp_display)
>
>         drm_connector_attach_encoder(connector, dp_display->encoder);
>
> -       if (dp_display->panel_bridge) {
> -               ret = drm_bridge_attach(dp_display->encoder,
> -                                       dp_display->panel_bridge, NULL,
> -                                       DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> -               if (ret < 0) {
> -                       DRM_ERROR("failed to attach panel bridge: %d\n", ret);
> -                       return ERR_PTR(ret);
> -               }
> -       }
> -
>         return connector;
>  }
>
> @@ -246,5 +236,16 @@ struct drm_bridge *msm_dp_bridge_init(struct msm_dp *dp_display, struct drm_devi
>                 return ERR_PTR(rc);
>         }
>
> +       if (dp_display->panel_bridge) {
> +               rc = drm_bridge_attach(dp_display->encoder,
> +                                       dp_display->panel_bridge, bridge,
> +                                       DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> +               if (rc < 0) {
> +                       DRM_ERROR("failed to attach panel bridge: %d\n", rc);
> +                       drm_bridge_remove(bridge);
> +                       return ERR_PTR(rc);
> +               }
> +       }
> +
>         return bridge;

Not a problem with this patch, but what is this pointer used for? I see
it's assigned to priv->bridges and num_bridges is incremented but nobody
seems to look at that.