linux-kernel - Re: [PATCH 4/9] drm/omapdrm: use drm_bridge_chain_get_last

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Message-ID: <20250714123240.16d8dcb1@booty>
Date: Mon, 14 Jul 2025 12:32:40 +0200
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Maxime Ripard <mripard@...nel.org>
Cc: Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong
 <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, Laurent
 Pinchart <Laurent.pinchart@...asonboard.com>, Jonas Karlman
 <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann
 <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter
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 <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix
 Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>,
 Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, Philipp Zabel
 <p.zabel@...gutronix.de>, Hui Pu <Hui.Pu@...ealthcare.com>, Thomas
 Petazzoni <thomas.petazzoni@...tlin.com>, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 4/9] drm/omapdrm: use drm_bridge_chain_get_last_bridge()

Hi Maxime,

On Thu, 10 Jul 2025 09:13:46 +0200
Maxime Ripard <mripard@...nel.org> wrote:

> On Wed, Jul 09, 2025 at 06:48:03PM +0200, Luca Ceresoli wrote:
> > Use drm_bridge_chain_get_last_bridge() instead of open coding a loop with
> > two invocations of drm_bridge_get_next_bridge() per iteration.
> > 
> > Besides being cleaner and more efficient, this change is necessary in
> > preparation for drm_bridge_get_next_bridge() to get a reference to the
> > returned bridge.
> > 
> > Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> > ---
> >  drivers/gpu/drm/omapdrm/omap_drv.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/omapdrm/omap_drv.c b/drivers/gpu/drm/omapdrm/omap_drv.c
> > index 054b71dba6a75b8c42198c4b102a093f43a675a2..3bbcec01428a6f290afdfa40ef6f79629539a584 100644
> > --- a/drivers/gpu/drm/omapdrm/omap_drv.c
> > +++ b/drivers/gpu/drm/omapdrm/omap_drv.c
> > @@ -378,12 +378,12 @@ static int omap_display_id(struct omap_dss_device *output)
> >  	struct device_node *node = NULL;
> >  
> >  	if (output->bridge) {
> > -		struct drm_bridge *bridge = output->bridge;
> > -
> > -		while (drm_bridge_get_next_bridge(bridge))
> > -			bridge = drm_bridge_get_next_bridge(bridge);
> > +		struct drm_bridge *bridge =
> > +			drm_bridge_chain_get_last_bridge(output->bridge->encoder);
> >  
> >  		node = bridge->of_node;
> > +
> > +		drm_bridge_put(bridge);  
> 
> Any reason you're not using __free(drm_bridge_put) here?

Just because the code is simple enough that an explicit
drm_bridge_put() is clearly sufficient.

Do you think __free() should be used even in such trivial cases?

Luca

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com