linux-kernel - Re: [PATCH v1 2/2] drm/msm/dp: add mutex to protect internal_hpd against race condition between different threads

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Message-ID: <CAE-0n532y=ARQ_+urEA_b3zUn+gKTu1fgK_siHNt3CpbLB9PZg@mail.gmail.com>
Date:   Wed, 10 May 2023 15:46:58 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>, agross@...nel.org,
        airlied@...il.com, andersson@...nel.org, daniel@...ll.ch,
        dianders@...omium.org, dmitry.baryshkov@...aro.org,
        dri-devel@...ts.freedesktop.org, robdclark@...il.com,
        sean@...rly.run, vkoul@...nel.org
Cc:     quic_abhinavk@...cinc.com, quic_jesszhan@...cinc.com,
        quic_sbillaka@...cinc.com, marijn.suijten@...ainline.org,
        freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/2] drm/msm/dp: add mutex to protect internal_hpd
 against race condition between different threads

Quoting Kuogee Hsieh (2023-05-10 13:31:05)
> Intrenal_hpd is referenced by event thread but set by drm bridge callback
> context. Add mutex to protect internal_hpd to avoid conflicts between
> threads.
>
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---

This patch looks completely unnecessary. How can dp_bridge_hpd_enable()
be called at the same time that dp_bridge_hpd_disable() is called or
dp_bridge_hpd_notify() is called? Isn't there locking or ordering at a
higher layer?