linux-kernel - Re: [PATCH v1 2/2] drm/msm/dp: do not stop transmitting phy test pattern during DP phy compliance test

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Date:   Mon, 25 Apr 2022 16:42:42 -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,
        dmitry.baryshkov@...aro.org, dri-devel@...ts.freedesktop.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,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] drm/msm/dp: do not stop transmitting phy test
 pattern during DP phy compliance test

Quoting Kuogee Hsieh (2022-04-25 15:11:03)
> At normal operation, transmit phy test pattern has to be terminated before
> DP controller switch to video ready state. However during phy compliance
> testing, transmit phy test pattern should not be terminated until end of
> compliance test which usually indicated by unplugged interrupt.

And what does the patch do to fix it? We need more details in the commit
text. I think it should continue with:

Only stop sending the train pattern in dp_ctrl_on_stream() if we're not
doing compliance testing. We also no longer reset 'p_level' and
'v_level' because XYZ and it's OK/better to retrain the link after
enabling the stream clks because XYZ.

>
> Fixes: 64e190e720a7 ("drm/msm/dp: DisplayPort PHY compliance tests fixup")

Should be

Fixes: 6625e2637d93 ("drm/msm/dp: DisplayPort PHY compliance tests fixup")

> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index 193cc1a..f99e173 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1699,8 +1699,6 @@ int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
>                 ctrl->link->link_params.rate,
>                 ctrl->link->link_params.num_lanes, ctrl->dp_ctrl.pixel_rate);
>
> -       ctrl->link->phy_params.p_level = 0;
> -       ctrl->link->phy_params.v_level = 0;

Why is this removed? Can you mention in the commit text why we don't
need to zero it out anymore?

>
>         rc = dp_ctrl_enable_mainlink_clocks(ctrl);
>         if (rc)
> @@ -1822,12 +1820,6 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>                 }
>         }
>
> -       if (!dp_ctrl_channel_eq_ok(ctrl))
> -               dp_ctrl_link_retrain(ctrl);
> -
> -       /* stop txing train pattern to end link training */
> -       dp_ctrl_clear_training_pattern(ctrl);
> -
>         ret = dp_ctrl_enable_stream_clocks(ctrl);
>         if (ret) {
>                 DRM_ERROR("Failed to start pixel clocks. ret=%d\n", ret);
> @@ -1839,6 +1831,13 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>                 return 0;
>         }
>
> +       if (!dp_ctrl_channel_eq_ok(ctrl)) {
> +               dp_ctrl_link_retrain(ctrl);
> +       }

Braces not needed. Please remove.

> +
> +       /* stop txing train pattern to end link training */
> +       dp_ctrl_clear_training_pattern(ctrl);
> +