linux-kernel - Re: [PATCH v4 24/27] drm/panel: panel-simple: Cache the EDID as long as we retain power

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Message-ID: <CAD=FV=UhOKcSC5FPPZgXiqfFCYOu4iFGrhtrgfGz_ovT8Qi-6w@mail.gmail.com>
Date:   Fri, 23 Apr 2021 09:30:36 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Sam Ravnborg <sam@...nborg.org>, Wolfram Sang <wsa@...nel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Rob Clark <robdclark@...omium.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Stanislav Lisovskiy <stanislav.lisovskiy@...el.com>,
        Steev Klimaszewski <steev@...i.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linus W <linus.walleij@...aro.org>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...ux.ie>,
        Thierry Reding <thierry.reding@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 24/27] drm/panel: panel-simple: Cache the EDID as long
 as we retain power

Hi,

On Fri, Apr 23, 2021 at 9:12 AM Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
>
> On Fri 16 Apr 17:39 CDT 2021, Douglas Anderson wrote:
>
> > It doesn't make sense to go out to the bus and read the EDID over and
> > over again. Let's cache it and throw away the cache when we turn power
> > off from the panel. Autosuspend means that even if there are several
> > calls to read the EDID before we officially turn the power on then we
> > should get good use out of this cache.
> >
> > Signed-off-by: Douglas Anderson <dianders@...omium.org>
> > ---
> >
> > (no changes since v1)
> >
> >  drivers/gpu/drm/panel/panel-simple.c | 17 ++++++++++-------
> >  1 file changed, 10 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> > index 40382c1be692..5a2953c4ca44 100644
> > --- a/drivers/gpu/drm/panel/panel-simple.c
> > +++ b/drivers/gpu/drm/panel/panel-simple.c
> > @@ -189,6 +189,8 @@ struct panel_simple {
> >       struct gpio_desc *enable_gpio;
> >       struct gpio_desc *hpd_gpio;
> >
> > +     struct edid *edid;
> > +
> >       struct drm_display_mode override_mode;
> >
> >       enum drm_panel_orientation orientation;
> > @@ -345,6 +347,9 @@ static int panel_simple_suspend(struct device *dev)
> >       regulator_disable(p->supply);
> >       p->unprepared_time = ktime_get();
> >
> > +     kfree(p->edid);
> > +     p->edid = NULL;
>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>
>
>
> But separate of this, shouldn't the driver have a pm_runtime_disable()
> in the remove path to synchronize the autosleep? Or is that not how that
> works?

Indeed! I'll add a patch to the start of my v5 (coming shortly) that
fixes this. Thanks for catching!

-Doug