From: Stephen Boyd <swboyd@chromium.org>
To: khsieh@codeaurora.org
Cc: robdclark@gmail.com, sean@poorly.run, tanmay@codeaurora.org,
abhinavk@codeaurora.org, aravindh@codeaurora.org,
airlied@linux.ie, daniel@ffwll.ch, linux-arm-msm@vger.kernel.org,
dri-devel@lists.freedesktop.org, freedreno@lists.freedesktop.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/msm/dp: fixes wrong connection state caused by failure of link train
Date: Mon, 05 Oct 2020 17:53:06 -0700 [thread overview]
Message-ID: <160194558634.310579.5267169787902306024@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <0de13a805820e4d73b8f906682386845@codeaurora.org>
Quoting khsieh@codeaurora.org (2020-10-05 11:02:10)
> >> + dp_del_event(dp_display, EV_DISCONNECT_PENDING_TIMEOUT);
> >> +
> >> dp_display_disable(dp_display, 0);
> >>
> >> rc = dp_display_unprepare(dp);
> >> if (rc)
> >> DRM_ERROR("DP display unprepare failed, rc=%d\n", rc);
> >>
> >> - dp_del_event(dp_display, EV_DISCONNECT_PENDING_TIMEOUT);
> >> -
> >> state = atomic_read(&dp_display->hpd_state);
> >> if (state == ST_DISCONNECT_PENDING) {
> >
> > I don't understand the atomic nature of this hpd_state variable. Why is
> > it an atomic variable? Is taking a spinlock bad? What is to prevent the
> > atomic read here to not be interrupted and then this if condition check
> > be invalid because the variable has been updated somewhere else?
> hpd_state variable updated by multiple threads. however it was protected
> by mutex.
> in theory, it should also work as u32. since it was declared as atomic
> from beginning
> and it does not cause any negative effects, can we keep it as it is?
>
It does cause negative effects by generating worse code for something
that is already protected from concurrency by a mutex. Can we make it an
enum and name the enum and then add a comment indicating that the
'event_mutex' lock protects this variable?
prev parent reply other threads:[~2020-10-06 0:53 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 22:09 [PATCH] drm/msm/dp: fixes wrong connection state caused by failure of link train Kuogee Hsieh
2020-10-03 2:12 ` Stephen Boyd
2020-10-05 18:02 ` khsieh
2020-10-06 0:53 ` Stephen Boyd [this message]
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