linux-kernel - Re: [PATCH v2] drm: of: Properly try all possible cases for bridge/panel detection

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Message-ID: <20220321091236.5rcottkhtztvijpl@houat>
Date:   Mon, 21 Mar 2022 10:12:36 +0100
From:   Maxime Ripard <maxime@...no.tech>
To:     Paul Kocialkowski <paul.kocialkowski@...tlin.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Linus Walleij <linus.walleij@...aro.org>,
        Jagan Teki <jagan@...rulasolutions.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Subject: Re: [PATCH v2] drm: of: Properly try all possible cases for
 bridge/panel detection

On Fri, Mar 18, 2022 at 05:22:46PM +0100, Paul Kocialkowski wrote:
> On Fri 18 Mar 22, 17:18, Maxime Ripard wrote:
> > On Fri, Mar 18, 2022 at 05:02:49PM +0100, Paul Kocialkowski wrote:
> > > While bridge/panel detection was initially relying on the usual
> > > port/ports-based of graph detection, it was recently changed to
> > > perform the lookup on any child node that is not port/ports
> > > instead when such a node is available, with no fallback on the
> > > usual way.
> > > 
> > > This results in breaking detection when a child node is present
> > > but does not contain any panel or bridge node, even when the
> > > usual port/ports-based of graph is there.
> > > 
> > > In order to support both situations properly, this commit reworks
> > > the logic to try both options and not just one of the two: it will
> > > only return -EPROBE_DEFER when both have failed.
> > > 
> > > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@...tlin.com>
> > > Fixes: 80253168dbfd ("drm: of: Lookup if child node has panel or bridge")
> > > ---
> > > 
> > > Changes since v1:
> > > - Renamed remote to node;
> > > - Renamed helper to find_panel_or_bridge;
> > > - Cleared bridge pointer early;
> > > - Returned early to make the code more concise;
> > > 
> > > ---
> > >  drivers/gpu/drm/drm_of.c | 98 ++++++++++++++++++++--------------------
> > >  1 file changed, 49 insertions(+), 49 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_of.c b/drivers/gpu/drm/drm_of.c
> > > index 9d90cd75c457..63137c833b7a 100644
> > > --- a/drivers/gpu/drm/drm_of.c
> > > +++ b/drivers/gpu/drm/drm_of.c
> > > @@ -219,6 +219,28 @@ int drm_of_encoder_active_endpoint(struct device_node *node,
> > >  }
> > >  EXPORT_SYMBOL_GPL(drm_of_encoder_active_endpoint);
> > >  
> > > +static int find_panel_or_bridge(struct device_node *node,
> > > +				struct drm_panel **panel,
> > > +				struct drm_bridge **bridge)
> > > +{
> > > +	if (panel) {
> > > +		*panel = of_drm_find_panel(node);
> > > +		if (!IS_ERR(*panel))
> > > +			return 0;
> > > +		else
> > > +			*panel = NULL;
> > 
> > You don't need the else branch here, we already cleared panel in
> > drm_of_find_panel_or_bridge
> 
> I think we do, because of_drm_find_panel doesn't return NULL when an error
> happens but PTR_ERR(), so we need to clear it to keep up with previous
> expectations.

Ah, right. We should remove the else then, checkpatch complains about it.

Maxime

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