linux-kernel - Re: [PATCH] drm/msm/dp: skip checking LINK_STATUS

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Message-ID: <160323215566.884498.14018580767640192186@swboyd.mtv.corp.google.com>
Date:   Tue, 20 Oct 2020 15:15:55 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <khsieh@...eaurora.org>, robdclark@...il.com,
        sean@...rly.run
Cc:     tanmay@...eaurora.org, abhinavk@...eaurora.org,
        aravindh@...eaurora.org, khsieh@...eaurora.org, airlied@...ux.ie,
        daniel@...ll.ch, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm/dp: skip checking LINK_STATUS_UPDATED bit

Quoting Kuogee Hsieh (2020-10-20 09:59:59)
> No need to check LINK_STATuS_UPDATED bit before

LINK_STATUS_UPDATED?

> return 6 bytes of link status during link training.

Why?

> This patch also fix phy compliance test link rate
> conversion error.

How?

> 
> Signed-off-by: Kuogee Hsieh <khsieh@...eaurora.org>
> ---

Any Fixes: tag?

>  drivers/gpu/drm/msm/dp/dp_ctrl.c | 20 ++++++--------------
>  drivers/gpu/drm/msm/dp/dp_link.c | 24 +++++++++++-------------
>  2 files changed, 17 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> index 6bdaec778c4c..76e891c91c6e 100644
> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
> @@ -1061,23 +1061,15 @@ static bool dp_ctrl_train_pattern_set(struct dp_ctrl_private *ctrl,
>  static int dp_ctrl_read_link_status(struct dp_ctrl_private *ctrl,
>                                     u8 *link_status)
>  {
> -       int len = 0;
> -       u32 const offset = DP_LANE_ALIGN_STATUS_UPDATED - DP_LANE0_1_STATUS;
> -       u32 link_status_read_max_retries = 100;
> -
> -       while (--link_status_read_max_retries) {
> -               len = drm_dp_dpcd_read_link_status(ctrl->aux,
> -                       link_status);
> -               if (len != DP_LINK_STATUS_SIZE) {
> -                       DRM_ERROR("DP link status read failed, err: %d\n", len);
> -                       return len;
> -               }
> +       int ret = 0, len;
>  
> -               if (!(link_status[offset] & DP_LINK_STATUS_UPDATED))
> -                       return 0;
> +       len = drm_dp_dpcd_read_link_status(ctrl->aux, link_status);
> +       if (len != DP_LINK_STATUS_SIZE) {
> +               DRM_ERROR("DP link status read failed, err: %d\n", len);
> +               ret = len;

Could this be positive if the len is greater than 0 but not
DP_LINK_STATUS_SIZE? Maybe the check should be len < 0? We certainly
don't want to return some smaller size from this function, right?

>         }
>  
> -       return -ETIMEDOUT;
> +       return ret;
>  }
>  
>  static int dp_ctrl_link_train_1(struct dp_ctrl_private *ctrl,
> diff --git a/drivers/gpu/drm/msm/dp/dp_link.c b/drivers/gpu/drm/msm/dp/dp_link.c
> index c811da515fb3..58d65daae3b3 100644
> --- a/drivers/gpu/drm/msm/dp/dp_link.c
> +++ b/drivers/gpu/drm/msm/dp/dp_link.c
> @@ -773,7 +773,8 @@ static int dp_link_process_link_training_request(struct dp_link_private *link)
>                         link->request.test_lane_count);
>  
>         link->dp_link.link_params.num_lanes = link->request.test_lane_count;
> -       link->dp_link.link_params.rate = link->request.test_link_rate;
> +       link->dp_link.link_params.rate =
> +               drm_dp_bw_code_to_link_rate(link->request.test_link_rate);

Why are we storing bw_code in test_link_rate? This looks very confusing.

>  
>         return 0;
>  }