Message-ID: <5afe209a-31d8-25d3-d087-2ff85eace182@quicinc.com>
Date:   Tue, 14 Jun 2022 15:28:34 -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 v6] drm/msm/dp: force link training for display resolution
 change


On 6/14/2022 2:59 PM, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2022-06-14 14:05:02)
>> Display resolution change is implemented through drm modeset. Older
>> modeset (resolution) has to be disabled first before newer modeset
>> (resolution) can be enabled. Display disable will turn off both
>> pixel clock and main link clock so that main link have to be
>> re-trained during display enable to have new video stream flow
>> again. At current implementation, display enable function manually
>> kicks up irq_hpd_handle which will read panel link status and start
>> link training if link status is not in sync state.
>>
>> However, there is rare case that a particular panel links status keep
>> staying in sync for some period of time after main link had been shut
>> down previously at display disabled. In this case, main link retraining
>> will not be executed by irq_hdp_handle(). Hence video stream of newer
>> display resolution will fail to be transmitted to panel due to main
>> link is not in sync between host and panel.
>>
>> This patch will bypass irq_hpd_hanle() in favor of directly call
> s/hanle/handle/
>
>> dp_ctrl_on_stream() to always perform link training in regardless of
>> main link status. So that no unexpected exception resolution change
>> failure cases will happen. Also this implementation are more efficient
>> than manual kicking off irq_hpd_handle function.
>>
>> Changes in v2:
>> -- set force_link_train flag on DP only (is_edp == false)
>>
>> Changes in v3:
>> -- revise commit  text
>> -- add Fixes tag
>>
>> Changes in v4:
>> -- revise commit  text
>>
>> Changes in v5:
>> -- fix spelling at commit text
>>
>> Changes in v6:
>> -- split dp_ctrl_on_stream() for phy test case
>> -- revise commit text for modeset
>>
>> Fixes: 62671d2ef24b ("drm/msm/dp: fixes wrong connection state caused by failure of link train")
>> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
>> ---
>>   drivers/gpu/drm/msm/dp/dp_ctrl.c    | 31 +++++++++++++++++++++++--------
>>   drivers/gpu/drm/msm/dp/dp_ctrl.h    |  3 ++-
>>   drivers/gpu/drm/msm/dp/dp_display.c | 13 ++++++-------
>>   3 files changed, 31 insertions(+), 16 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dp/dp_ctrl.c b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> index af7a80c..cb9c7af 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_ctrl.c
>> @@ -1807,7 +1807,27 @@ static int dp_ctrl_link_retrain(struct dp_ctrl_private *ctrl)
>>          return dp_ctrl_setup_main_link(ctrl, &training_step);
>>   }
>>
>> -int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>> +int dp_ctrl_on_stream_phy_test_report(struct dp_ctrl *dp_ctrl)
>> +{
>> +       int ret = 0;
> Drop assignment please.
>
>> +       struct dp_ctrl_private *ctrl;
>> +
>> +       ctrl = container_of(dp_ctrl, struct dp_ctrl_private, dp_ctrl);
>> +
>> +       ctrl->dp_ctrl.pixel_rate = ctrl->panel->dp_mode.drm_mode.clock;
>> +
>> +       ret = dp_ctrl_enable_stream_clocks(ctrl);
>> +       if (ret) {
>> +               DRM_ERROR("Failed to start pixel clocks. ret=%d\n", ret);
>> +               return ret;
>> +       }
>> +
>> +       dp_ctrl_send_phy_test_pattern(ctrl);
> None of this code needs to be run in the normal display on case?
>
>> +
>> +       return 0;
>> +}
>> +
>> +int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl, bool force_link_train)
>>   {
>>          int ret = 0;
>>          bool mainlink_ready = false;
>> @@ -1843,12 +1863,7 @@ int dp_ctrl_on_stream(struct dp_ctrl *dp_ctrl)
>>                  goto end;
>>          }
>>
>> -       if (ctrl->link->sink_request & DP_TEST_LINK_PHY_TEST_PATTERN) {
>> -               dp_ctrl_send_phy_test_pattern(ctrl);
>> -               return 0;
>> -       }
>> -
>> -       if (!dp_ctrl_channel_eq_ok(ctrl))
>> +       if (force_link_train || !dp_ctrl_channel_eq_ok(ctrl))
>>                  dp_ctrl_link_retrain(ctrl);
>>
>>          /* stop txing train pattern to end link training */
>> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
>> index c388323..b6d25ab 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_display.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
>> @@ -1688,10 +1689,12 @@ void dp_bridge_enable(struct drm_bridge *drm_bridge)
>>
>>          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 = true;
>> +       }
>>
>> -       dp_display_enable(dp_display, 0);
>> +       dp_display_enable(dp_display, force_link_train);
> Do we need to pass it from here? Why can't dp_display_enable() simply
> check for 'state == ST_DISPLAY_OFF' and then force retrain the link?

can we keep this as it is?

it is more readable that we do need force link re-training due to 
ST_DISPLAY_OFF at top level.

Also we only need to do (state == ST_DISPLAY_OFF) checking one time.

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