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

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Message-ID: <YjSx1rNLTh/L3MQQ@aptenodytes>
Date:   Fri, 18 Mar 2022 17:22:46 +0100
From:   Paul Kocialkowski <paul.kocialkowski@...tlin.com>
To:     Maxime Ripard <maxime@...no.tech>
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

Hi Maxime,

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.

> Looks good otherwise, thanks!

Great, thanks for the review!

Paul

-- 
Paul Kocialkowski, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com

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