linux-kernel - Re: [PATCH v2 2/7] drm/msm/dp: reduce link rate if failed at link training 1

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Date:   Thu, 22 Jul 2021 19:05:30 +0000
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <khsieh@...eaurora.org>,
        dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run
Cc:     abhinavk@...eaurora.org, aravindh@...eaurora.org, airlied@...ux.ie,
        daniel@...ll.ch, bjorn.andersson@...aro.org,
        linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/7] drm/msm/dp: reduce link rate if failed at link
 training 1

Quoting Kuogee Hsieh (2021-07-13 08:54:02)
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index 27fb0f0..92cf331 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1634,6 +1617,24 @@ void dp_ctrl_handle_sink_request(struct dp_ctrl *dp_ctrl)
>         }
>  }
>
> +static bool dp_ctrl_clock_recovery_any_ok(
> +                       const u8 link_status[DP_LINK_STATUS_SIZE],
> +                       int lane_count)
> +{
> +       int lane_cnt;
> +
> +       /*
> +        * only interested in the lane number after reduced
> +        * lane_cnt = 4, then only interested in 2 lanes
> +        * lane_cnt = 2, then only interested in 1 lane
> +        */
> +       lane_cnt = lane_count >> 1;
> +       if (lane_cnt == 0)
> +               return false;
> +
> +       return drm_dp_clock_recovery_ok(link_status, lane_count);

This doesn't work? Because drm_dp_clock_recovery_ok() requires every
lane to be OK whereas this function wants any lane to be OK? It may make
sense to have drm_dp_clock_recovery_ok() return false if lane_count == 0
too.

> +}
> +
>  int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl)
>  {
>         int rc = 0;