linux-kernel - Re: [PATCH v5 08/10] drm/bridge: samsung-dsim: use supporting variable for out

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Message-ID: <20250110115819.55bc887b@booty>
Date: Fri, 10 Jan 2025 11:58:19 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Simona Vetter <simona@...ll.ch>, Inki Dae <inki.dae@...sung.com>, Jagan
 Teki <jagan@...rulasolutions.com>, Marek Szyprowski
 <m.szyprowski@...sung.com>, Catalin Marinas <catalin.marinas@....com>, Will
 Deacon <will@...nel.org>, Shawn Guo <shawnguo@...nel.org>, Sascha Hauer
 <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>,
 Fabio Estevam <festevam@...il.com>, Daniel Thompson <danielt@...nel.org>,
 Andrzej Hajda <andrzej.hajda@...el.com>, Jonathan Corbet <corbet@....net>,
 Paul Kocialkowski <contact@...lk.fr>, Maxime Ripard <mripard@...nel.org>,
 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>, Hervé Codina <herve.codina@...tlin.com>, Thomas Petazzoni
 <thomas.petazzoni@...tlin.com>, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org, linux-doc@...r.kernel.org, Paul
 Kocialkowski <paul.kocialkowski@...tlin.com>
Subject: Re: [PATCH v5 08/10] drm/bridge: samsung-dsim: use supporting
 variable for out_bridge

Hi Dmitry,

On Thu, 2 Jan 2025 13:01:49 +0100
Luca Ceresoli <luca.ceresoli@...tlin.com> wrote:

> > > diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> > > index f8b4fb8357659018ec0db65374ee5d05330639ae..c4d1563fd32019efde523dfc0863be044c05a826 100644
> > > --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> > > +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> > > @@ -1705,6 +1705,7 @@ static int samsung_dsim_host_attach(struct mipi_dsi_host *host,
> > >  	struct device *dev = dsi->dev;
> > >  	struct device_node *np = dev->of_node;
> > >  	struct device_node *remote;
> > > +	struct drm_bridge *out_bridge;
> > >  	struct drm_panel *panel;
> > >  	int ret;
> > >  
> > > @@ -1740,21 +1741,23 @@ static int samsung_dsim_host_attach(struct mipi_dsi_host *host,
> > >  
> > >  	panel = of_drm_find_panel(remote);
> > >  	if (!IS_ERR(panel)) {
> > > -		dsi->out_bridge = devm_drm_panel_bridge_add(dev, panel);
> > > +		out_bridge = devm_drm_panel_bridge_add(dev, panel);
> > >  	} else {
> > > -		dsi->out_bridge = of_drm_find_bridge(remote);
> > > -		if (!dsi->out_bridge)
> > > -			dsi->out_bridge = ERR_PTR(-EINVAL);
> > > +		out_bridge = of_drm_find_bridge(remote);
> > > +		if (!out_bridge)
> > > +			out_bridge = ERR_PTR(-EINVAL);
> > >  	}    
> > 
> > While looking at this patch, I think we should migrate the driver to
> > drm_of_find_panel_or_bridge().  
> 
> Indeed, the code here is duplicating drm_of_find_panel_or_bridge(). I'm
> going to convert it.

Or maybe not. A similar work has been attempted in the past [0] and
then reverted. There are many subtleties one would need to take care of
before getting this right, I don't think opening this other can of
worms in the middle of the bridge refcounting work makes sense.

[0] https://patchwork.freedesktop.org/patch/482751/

Luca

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