linux-kernel - Re: [PATCH v3 2/2] drm/bridge: analogix

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Date:   Tue, 1 Mar 2022 18:03:18 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        Sean Paul <sean@...rly.run>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>
Subject: Re: [PATCH v3 2/2] drm/bridge: analogix_dp: Enable autosuspend

On Tue, Feb 22, 2022 at 2:10 PM Doug Anderson <dianders@...omium.org> wrote:
> On Thu, Feb 17, 2022 at 2:42 PM Brian Norris <briannorris@...omium.org> wrote:
> > --- a/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> > +++ b/drivers/gpu/drm/bridge/analogix/analogix_dp_core.c
> > @@ -1121,7 +1121,7 @@ static int analogix_dp_get_modes(struct drm_connector *connector)
> >
> >                 pm_runtime_get_sync(dp->dev);
> >                 edid = drm_get_edid(connector, &dp->aux.ddc);
> > -               pm_runtime_put(dp->dev);
> > +               pm_runtime_put_autosuspend(dp->dev);
>
> So I think you can fully get rid of these ones now and rely on the
> ones in the aux transfer, right?

Yep, good catch.

> >                 if (edid) {
> >                         drm_connector_update_edid_property(&dp->connector,
> >                                                            edid);
> > @@ -1642,7 +1642,7 @@ static ssize_t analogix_dpaux_transfer(struct drm_dp_aux *aux,
> >
> >         ret = analogix_dp_transfer(dp, msg);
> >  out:
> > -       pm_runtime_put(dp->dev);
> > +       pm_runtime_put_autosuspend(dp->dev);
> >
> >         return ret;
> >  }
> > @@ -1775,6 +1775,8 @@ int analogix_dp_bind(struct analogix_dp_device *dp, struct drm_device *drm_dev)
> >         if (ret)
> >                 return ret;
> >
> > +       pm_runtime_use_autosuspend(dp->dev);
> > +       pm_runtime_set_autosuspend_delay(dp->dev, 100);
>
> It's explicitly listed in the Documentation that you need the
> corresponding pm_runtime_dont_use_autosuspend(). Specifically, it
> says:
>
> > Drivers in ->remove() callback should undo the runtime PM changes done
> > in ->probe(). Usually this means calling pm_runtime_disable(),
> > pm_runtime_dont_use_autosuspend() etc.
>
> Not that it's very common to see anyone actually get it right, but I
> seem to remember running into an issue when I didn't do it. I think
> ti-sn65dsi86 still has it wrong since I found out about this later.
> Need to write a patch up for that... Basically you want to put it
> right before the two calls in your driver to pm_runtime_disable().

Ack.

Speaking of API misfeatures that we missed: I've failed to call
pm_runtime_mark_last_busy(). I'll add that in the next rev, for the
cases where we weren't already calling *_put_sync() (i.e., presumably
we don't really care to wait around for autosuspend).

*gripe* What a silly API. *gripe*

Brian