linux-kernel - Re: [PATCH 30/40] drm/rockchip: Flush PSR before committing modeset disables/enables

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Date:   Tue, 16 Jan 2018 13:02:40 +0900
From:   Tomasz Figa <tfiga@...omium.org>
To:     Thierry Escande <thierry.escande@...labora.com>
Cc:     Archit Taneja <architt@...eaurora.org>,
        Inki Dae <inki.dae@...sung.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Sandy Huang <hjc@...k-chips.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        Haixia Shi <hshi@...omium.org>,
        Ørjan Eide <orjan.eide@....com>,
        zain wang <wzz@...k-chips.com>,
        Yakir Yang <ykk@...k-chips.com>, Lin Huang <hl@...k-chips.com>,
        Douglas Anderson <dianders@...omium.org>,
        Mark Yao <mark.yao@...k-chips.com>,
        linux-kernel@...r.kernel.org,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH 30/40] drm/rockchip: Flush PSR before committing modeset disables/enables

Hi Thierry,

On Tue, Jan 16, 2018 at 2:16 AM, Thierry Escande
<thierry.escande@...labora.com> wrote:
> From: Tomasz Figa <tfiga@...omium.org>
>
> Currently PSR flush is triggered from CRTC's .atomic_begin() callback,
> which is executed after modeset disables and enables and before plane
> updates are committed. Since PSR flush and re-enable can be triggered
> asynchronously by external sources (input event, delayed work), it can
> race with hardware programming done in the aforementioned stages.
>
> To avoid the race, we can trigger PSR flush before committing modeset
> disables/enables. This also has the advantage of removing some
> PSR-specific knowledge from the VOP driver.

FYI, this patch was eventually found to still leave few unsolved races
and was later replaced with a more comprehensive redesign of Rockchip
PSR code. Please refer to the following Chromium patches:

https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/430429/
https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/436571/
https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/438228/
https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/438229/
<- This one effectively replaces all the code added in this patch.
https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/438230/

Best regards,
Tomasz