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

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Date:   Fri, 30 Oct 2020 15:06:33 -0700
From:   khsieh@...eaurora.org
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     robdclark@...il.com, sean@...rly.run, tanmay@...eaurora.org,
        abhinavk@...eaurora.org, aravindh@...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

On 2020-10-20 15:15, Stephen Boyd wrote:
> 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?
> 

no, it should be exactly the byte number requested to read.
otherwise, it should be failed and will re read at next run.

>>         }
>> 
>> -       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.

Test_link_rate contains link rate from dpcd read. it need to be convert 
to real
rate by timing 2.7Mb before start phy compliance test.

> 
>> 
>>         return 0;
>>  }