[Freedreno] [PATCH] drm/msm/dp: force link training for display resolution change

[Stephen Boyd]

Quoting Kuogee Hsieh (2022-05-26 10:26:18)
> During display resolution changes display have to be disabled first
> followed by display enable with new resolution. This patch force
> main link always be retrained during display enable procedure to
> simplify implementation instead of manually kicking of irq_hpd
> handle.

How is that better? Can you please describe how it improves things? I
suppose it avoids some round trips through the event queue just to turn
on the display?

>
> Signed-off-by: Kuogee Hsieh <quic_khsieh at quicinc.com>

Any Fixes tag? Or it's not fixing anything, just making things simpler?

> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index 5ddb4e8..8b71013 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.h b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> index 2433edb..dcc7af21 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.h
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.h
> @@ -20,7 +20,7 @@ struct dp_ctrl {
>  };
>
>  int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl);
> -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl);
> +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train);

Can we have another API like dp_ctrl_on_stream_retrain()? Or name
'force_link_train' to 'retrain'?

>  int dp_ctrl_off_link_stream(struct dp_ctrl *dp_ctrl);
>  int dp_ctrl_off(struct dp_ctrl *dp_ctrl);
>  void dp_ctrl_push_idle(struct dp_ctrl *dp_ctrl);
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index bfc6581..9246421 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -892,7 +892,7 @@ static int dp_display_enable(struct dp_display_private *dp, u32 data)

Any reason why dp_display_enable() is forward declared and why it takes
a u32 data argument? It's not part of the eventqueue calling code from
what I can tell so we should be able to rename 'data' to 'retrain_link'?

>                 return 0;
>         }
>
> -       rc = dp_ctrl_on_stream(dp->ctrl);
> +       rc = dp_ctrl_on_stream(dp->ctrl, data);
>         if (!rc)
>                 dp_display->power_on = true;
>
> @@ -1594,6 +1594,7 @@ int msm_dp_display_enable(struct msm_dp *dp, struct drm_encoder *encoder)
>         int rc = 0;
>         struct dp_display_private *dp_display;
>         u32 state;
> +       bool force_link_train = false;
>
>         dp_display = container_of(dp, struct dp_display_private, dp_display);
>         if (!dp_display->dp_mode.drm_mode.clock) {
> @@ -1622,10 +1623,12 @@ int msm_dp_display_enable(struct msm_dp *dp, struct drm_encoder *encoder)
>
>         state =  dp_display->hpd_state;
>
> -       if (state == ST_DISPLAY_OFF)
> +       if (state == ST_DISPLAY_OFF) {
>                 dp_display_host_phy_init(dp_display);
> +               force_link_train = 1;

Use true instead of 1 if the type is a bool please.

> +       }
>
> -       dp_display_enable(dp_display, 0);
> +       dp_display_enable(dp_display, force_link_train);
>
>         rc = dp_display_post_enable(dp);
>         if (rc) {