linux-kernel - Re: [PATCH v9] drm/msm/dp: force link training for display resolution change

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Date:   Thu, 16 Jun 2022 16:39:29 -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 v9] drm/msm/dp: force link training for display resolution change

Quoting Kuogee Hsieh (2022-06-16 13:26:40)
> 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_handle() in favor of directly call
> 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
>
> Changes in v7:
> -- drop 0 assignment at local variable (ret = 0)
>
> Changes in v8:
> -- add patch to remove pixel_rate from dp_ctrl
>
> Changes in v9:
> -- forward declare dp_ctrl_on_stream_phy_test_report()
>
> Fixes: 62671d2ef24b ("drm/msm/dp: fixes wrong connection state caused by failure of link train")
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---

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