linux-kernel - Re: [PATCH v2 2/3] drm/msm/dp: do not re initialize of audio_comp at display

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Message-ID: <cf72c919404a5bb4d0bdf101a341b074@codeaurora.org>
Date:   Wed, 14 Apr 2021 10:55:09 -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 v2 2/3] drm/msm/dp: do not re initialize of audio_comp at
 display_disable()

On 2021-04-13 20:17, Stephen Boyd wrote:
> Quoting Kuogee Hsieh (2021-04-13 16:11:30)
>> At dongle unplug, dp initializes audio_comp followed by sending 
>> disconnect
>> event notification to audio and to make sure audio had shutdown 
>> completely
>> by wait for audio completion notification at display_disable(). This 
>> patch
> 
> Is this dp_display_disable()? Doubtful that display_disable() is the
> function we're talking about.
yes
> 
>> will not re initialize audio_comp at display_disable() if audio 
>> shutdown
>> is triggered by dongle unplugged.
> 
> This commit text seems to say the why before the what, where why is "dp
> initializes audio_comp followed by sending disconnect.." and the what 
> is
> "this patch will no re-initialized audio_comp...". Can you reorder this
> so the what comes before the why?
> 
ok
>> 
>> Signed-off-by: Kuogee Hsieh <khsieh@...eaurora.org>
>> ---
>>  drivers/gpu/drm/msm/dp/dp_display.c | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c 
>> b/drivers/gpu/drm/msm/dp/dp_display.c
>> index 0ba71c7..1d71c95 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_display.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
>> @@ -894,8 +894,10 @@ static int dp_display_disable(struct 
>> dp_display_private *dp, u32 data)
>>         /* wait only if audio was enabled */
>>         if (dp_display->audio_enabled) {
>>                 /* signal the disconnect event */
>> -               reinit_completion(&dp->audio_comp);
>> -               dp_display_handle_plugged_change(dp_display, false);
>> +               if (dp->hpd_state != ST_DISCONNECT_PENDING) {
>> +                       reinit_completion(&dp->audio_comp);
> 
> Why is this reinitialized here at all? Wouldn't it make more sense to
> initialize the completion once at cable plug in and then not initialize
> the completion anywhere else? Or initialize the completion whenever
> dp_display->audio_enabled is set to true and then only wait for the
> completion here if that boolean is true? Or initialize the completion
> when dp_display_handle_plugged_change() is passed true for the 
> 'plugged'
> argument?
> yes, i think it is better approach, this will take care of both unplug 
> and suspend.

> I started reading the code and quickly got lost figuring out how
> dp_display_handle_plugged_change() worked and the interaction between
> the dp display code and the audio codec embedded in here. There seem to
> be a couple of conditions that cut off things early, like
> dp_display->audio_enabled and audio->engine_on. Why? Why does
> dp_display_signal_audio_complete() call complete_all() vs. just
> complete()? Please help! :(
> 
>> +                       dp_display_handle_plugged_change(dp_display, 
>> false);
> 
> I think it's this way because dp_hpd_unplug_handle() is the function
> that sets the hpd_state to ST_DISCONNECT_PENDING and then reinitializes
> the completion (why?) and calls dp_display_handle_plugged_change(). So
> the commit text could say that reinitializing the completion again here
> at dp_display_disable() is racing with the audio code in the case that
> dp_hpd_unplug_handle() already called
> dp_display_handle_plugged_change() and it would make more sense. But 
> the
> question still stands why that race even exists in the first place vs.
> initializing the completion variable in only one place unconditionally
> when the cable is connected, in dp_hpd_plug_handle() or
> dp_display_post_enable().
> 
>> +               }
>>                 if (!wait_for_completion_timeout(&dp->audio_comp,
>>                                 HZ * 5))
>>                         DRM_ERROR("audio comp timeout\n");