linux-kernel - Re: [PATCH] drm/msm: Don't use autosuspend for display

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Message-ID: <CAF6AEGsrCssqo3v3uw00C0YmGAXd6DpqeCRpioqxKRkXeN27gg@mail.gmail.com>
Date:   Wed, 15 Dec 2021 12:13:52 -0800
From:   Rob Clark <robdclark@...il.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Rob Clark <robdclark@...omium.org>,
        Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jonathan Marek <jonathan@...ek.ca>,
        Jessica Zhang <quic_jesszhan@...cinc.com>,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        Rajeev Nandan <quic_rajeevny@...cinc.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm: Don't use autosuspend for display

On Wed, Dec 15, 2021 at 11:10 AM Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Rob Clark (2021-12-15 09:59:02)
> > From: Rob Clark <robdclark@...omium.org>
> >
> > No functional change, as we only actually enable autosuspend for the GPU
> > device.  But lets not encourage thinking that autosuspend is a good idea
> > for anything display related.
>
> I'd prefer to see a small blurb about why it's not a good idea to use
> autosuspend for display things. Then this commit can be dug out of the
> history and someone new can quickly understand the reasoning behind it.
> Just saying it's not a good idea doesn't really help.

The issue is that we have multiple different devices at play, and
potentially specific requirements about power sequencing when lighting
up or shutting down the display.. autosuspend would just turn that
into a giant race condition.  I'll squash something about this into
the commit msg

BR,
-R

> >
> > Signed-off-by: Rob Clark <robdclark@...omium.org>
> > ---
>
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>