linux-kernel - Re: [PATCH v6] drm/msm/dp: force link training for display resolution change

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Message-ID: <CAE-0n52EAyTcQd6CiwXT1T658C-b+2r14BK_3-tf-ZiJdzqaAw@mail.gmail.com>
Date:   Tue, 14 Jun 2022 14:59:06 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...ux.ie, bjorn.andersson@...aro.org, daniel@...ll.ch,
        dianders@...omium.org, dmitry.baryshkov@...aro.org,
        robdclark@...il.com, sean@...rly.run, vkoul@...nel.org
Cc:     quic_abhinavk@...cinc.com, quic_aravindh@...cinc.com,
        quic_sbillaka@...cinc.com, freedreno@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6] drm/msm/dp: force link training for display resolution change

Quoting Kuogee Hsieh (2022-06-14 14:05:02)
> Display resolution change is implemented through drm modeset. Older
> modeset (resolution) has to be disabled first before newer modeset
> (resolution) can be enabled. Display disable will turn off both
> pixel clock and main link clock so that main link have to be
> re-trained during display enable to have new video stream flow
> again. At current implementation, display enable function manually
> kicks up irq_hpd_handle which will read panel link status and start
> link training if link status is not in sync state.
>
> However, there is rare case that a particular panel links status keep
> staying in sync for some period of time after main link had been shut
> down previously at display disabled. In this case, main link retraining
> will not be executed by irq_hdp_handle(). Hence video stream of newer
> display resolution will fail to be transmitted to panel due to main
> link is not in sync between host and panel.
>
> This patch will bypass irq_hpd_hanle() in favor of directly call

s/hanle/handle/

> dp_ctrl_on_stream() to always perform link training in regardless of
> main link status. So that no unexpected exception resolution change
> failure cases will happen. Also this implementation are more efficient
> than manual kicking off irq_hpd_handle function.
>
> Changes in v2:
> -- set force_link_train flag on DP only (is_edp == false)
>
> Changes in v3:
> -- revise commit  text
> -- add Fixes tag
>
> Changes in v4:
> -- revise commit  text
>
> Changes in v5:
> -- fix spelling at commit text
>
> Changes in v6:
> -- split dp_ctrl_on_stream() for phy test case
> -- revise commit text for modeset
>
> Fixes: 62671d2ef24b ("drm/msm/dp: fixes wrong connection state caused by failure of link train")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c    | 31 +++++++++++++++++++++++--------
>  drivers/gpu/drm/msm/dp/dp_ctrl.h    |  3 ++-
>  drivers/gpu/drm/msm/dp/dp_display.c | 13 ++++++-------
>  3 files changed, 31 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index af7a80c..cb9c7af 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1807,7 +1807,27 @@ static int dp_ctrl_link_retrain(struct dp_ctrl_private *ctrl)
>         return dp_ctrl_setup_main_link(ctrl, &training_step);
>  }
>
> -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
> +int dp_ctrl_on_stream_phy_test_report(struct dp_ctrl *dp_ctrl)
> +{
> +       int ret = 0;

Drop assignment please.

> +       struct dp_ctrl_private *ctrl;
> +
> +       ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
> +
> +       ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
> +
> +       ret = dp_ctrl_enable_stream_clocks(ctrl);
> +       if (ret) {
> +               DRM_ERROR("Failed to start pixel clocks. ret=%d\n", ret);
> +               return ret;
> +       }
> +
> +       dp_ctrl_send_phy_test_pattern(ctrl);

None of this code needs to be run in the normal display on case?

> +
> +       return 0;
> +}
> +
> +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train)
>  {
>         int ret = 0;
>         bool mainlink_ready = false;
> @@ -1843,12 +1863,7 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>                 goto end;
>         }
>
> -       if (ctrl->link->sink_request & DP_TEST_LINK_PHY_TEST_PATTERN) {
> -               dp_ctrl_send_phy_test_pattern(ctrl);
> -               return 0;
> -       }
> -
> -       if (!dp_ctrl_channel_eq_ok(ctrl))
> +       if (force_link_train || !dp_ctrl_channel_eq_ok(ctrl))
>                 dp_ctrl_link_retrain(ctrl);
>
>         /* stop txing train pattern to end link training */
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index c388323..b6d25ab 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -1688,10 +1689,12 @@ void dp_bridge_enable(struct drm_bridge *drm_bridge)
>
>         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 = true;
> +       }
>
> -       dp_display_enable(dp_display, 0);
> +       dp_display_enable(dp_display, force_link_train);

Do we need to pass it from here? Why can't dp_display_enable() simply
check for 'state == ST_DISPLAY_OFF' and then force retrain the link?