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

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Date:   Fri, 27 May 2022 08:25:42 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     Stephen Boyd <swboyd@...omium.org>, <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] drm/msm/dp: force link training for display resolution
 change


On 5/26/2022 5:07 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-05-26 10:26:18)
>> During display resolution changes display have to be disabled first
>> followed by display enable with new resolution. This patch force
>> main link always be retrained during display enable procedure to
>> simplify implementation instead of manually kicking of irq_hpd
>> handle.
> How is that better? Can you please describe how it improves things? I
> suppose it avoids some round trips through the event queue just to turn
> on the display?

This try to fix customer issues which only happen on one particular 
panel which fails on display resolution changes sometimes.

I will add more description.

>
>> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> Any Fixes tag? Or it's not fixing anything, just making things simpler?
will add.
>
>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> index 5ddb4e8..8b71013 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.h b/drivers/gpu/drm/msm/dp/dp_ctrl.h
>> index 2433edb..dcc7af21 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.h
>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.h
>> @@ -20,7 +20,7 @@ struct dp_ctrl {
>>   };
>>
>>   int dp_ctrl_on_link(struct dp_ctrl *dp_ctrl);
>> -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl);
>> +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train);
> Can we have another API like dp_ctrl_on_stream_retrain()? Or name
> 'force_link_train' to 'retrain'?
>
>>   int dp_ctrl_off_link_stream(struct dp_ctrl *dp_ctrl);
>>   int dp_ctrl_off(struct dp_ctrl *dp_ctrl);
>>   void dp_ctrl_push_idle(struct dp_ctrl *dp_ctrl);
>> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
>> index bfc6581..9246421 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_display.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
>> @@ -892,7 +892,7 @@ static int dp_display_enable(struct dp_display_private *dp, u32 data)
> Any reason why dp_display_enable() is forward declared and why it takes
> a u32 data argument? It's not part of the eventqueue calling code from
> what I can tell so we should be able to rename 'data' to 'retrain_link'?
>
>>                  return 0;
>>          }
>>
>> -       rc = dp_ctrl_on_stream(dp->ctrl);
>> +       rc = dp_ctrl_on_stream(dp->ctrl, data);
>>          if (!rc)
>>                  dp_display->power_on = true;
>>
>> @@ -1594,6 +1594,7 @@ int msm_dp_display_enable(struct msm_dp *dp, struct drm_encoder *encoder)
>>          int rc = 0;
>>          struct dp_display_private *dp_display;
>>          u32 state;
>> +       bool force_link_train = false;
>>
>>          dp_display = container_of(dp, struct dp_display_private, dp_display);
>>          if (!dp_display->dp_mode.drm_mode.clock) {
>> @@ -1622,10 +1623,12 @@ int msm_dp_display_enable(struct msm_dp *dp, struct drm_encoder *encoder)
>>
>>          state =  dp_display->hpd_state;
>>
>> -       if (state == ST_DISPLAY_OFF)
>> +       if (state == ST_DISPLAY_OFF) {
>>                  dp_display_host_phy_init(dp_display);
>> +               force_link_train = 1;
> Use true instead of 1 if the type is a bool please.
>
>> +       }
>>
>> -       dp_display_enable(dp_display, 0);
>> +       dp_display_enable(dp_display, force_link_train);
>>
>>          rc = dp_display_post_enable(dp);
>>          if (rc) {