linux-kernel - Re: [PATCH 1/2] drm/msm/dp: postpone irq_hpd event during connection pending state

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Date:   Wed, 13 Jan 2021 15:44:32 -0800
From:   khsieh@...eaurora.org
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     dri-devel@...ts.freedesktop.org, 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, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] drm/msm/dp: postpone irq_hpd event during connection
 pending state

On 2021-01-13 12:22, Stephen Boyd wrote:
> Quoting khsieh@...eaurora.org (2021-01-13 09:44:24)
>> On 2021-01-11 11:55, Stephen Boyd wrote:
>> > Quoting Kuogee Hsieh (2021-01-07 12:30:24)
>> >> irq_hpd event can only be executed at connected state. Therefore
>> >> irq_hpd event should be postponed if it happened at connection
>> >> pending state. This patch also make sure both link rate and lane
>> >
>> > Why does it happen at connection pending state?
>> plug in need two state to complete it.
>> advance to connection pending state once link training completed and
>> sent uevent notification to frame work.
>> transition to connected state after frame work provided resolution
>> timing and start transmit video panel.
>> Therefore irq_hpd should not be handled if it occurred before 
>> connected
>> state.
> 
> Sure that's what's going on in the patch but you didn't answer my
> question. Why does irq_hpd happen before connected state?

I have no idea why it happen this way.
during debug 
https://partnerissuetracker.corp.google.com/issues/170598152
I saw two different scenario
1) irq_hpd followed by unplug with less than 20 ms in between. this one 
fixed by this patch set.
2) plug followed by irq_hpd around 300ms in between. it does not cause 
problem. but it should be handled in order (after connected state).