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 16:00:35 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     khsieh@...eaurora.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

Quoting khsieh@...eaurora.org (2021-01-13 15:44:32)
> 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).

Ok. So nobody understands why the hardware is acting this way and we're
papering over the problem by forcing the HPD state to be what we think
it should be? That's not great.