linux-kernel - Re: [PATCH 2/2] drm/bridge: fsl-ldb: make warning message more informative

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Message-ID: <20250307122212.18252ca6@booty>
Date: Fri, 7 Mar 2025 12:22:12 +0100
From: Luca Ceresoli <luca.ceresoli@...tlin.com>
To: Liu Ying <victor.liu@....com>
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>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Shawn Guo
 <shawnguo@...nel.org>, Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix
 Kernel Team <kernel@...gutronix.de>, Fabio Estevam <festevam@...il.com>,
 Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
 dri-devel@...ts.freedesktop.org, imx@...ts.linux.dev,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/bridge: fsl-ldb: make warning message more
 informative

Hello Liu,

thanks for your reviews.

On Fri, 7 Mar 2025 14:33:37 +0800
Liu Ying <victor.liu@....com> wrote:

> On 03/07/2025, Luca Ceresoli wrote:
> > This warning notifies a clock was set to an inaccurate value. Modify the
> > string to also show the clock name.
> > 
> > While doing that also rewrap the entire function call.
> > 
> > Signed-off-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> > ---
> >  drivers/gpu/drm/bridge/fsl-ldb.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/bridge/fsl-ldb.c b/drivers/gpu/drm/bridge/fsl-ldb.c
> > index 0fc8a14fd80062248a43b8b93272101a7ca6158a..c7c899a9644bb827845fb3fe96a9695d79a91474 100644
> > --- a/drivers/gpu/drm/bridge/fsl-ldb.c
> > +++ b/drivers/gpu/drm/bridge/fsl-ldb.c
> > @@ -181,9 +181,9 @@ static void fsl_ldb_atomic_enable(struct drm_bridge *bridge,
> >  
> >  	configured_link_freq = clk_get_rate(fsl_ldb->clk);
> >  	if (configured_link_freq != requested_link_freq)
> > -		dev_warn(fsl_ldb->dev, "Configured LDB clock (%lu Hz) does not match requested LVDS clock: %lu Hz\n",
> > -			 configured_link_freq,
> > -			 requested_link_freq);
> > +		dev_warn(fsl_ldb->dev,
> > +			 "Configured %pC clock (%lu Hz) does not match requested LVDS clock: %lu Hz\n",
> > +			 fsl_ldb->clk, configured_link_freq, requested_link_freq);  
> 
> Though this slightly changes the warning message userspace sees, I guess it is
> acceptable.
> 
> Does it make sense to s/%pC/%pCn/ so that the clock name is printed in lower
> case instead of upper case, since it seems that all i.MX specific clock names
> are in lower case?

%pC and %pCn print the same string, as I just discovered at
https://elixir.bootlin.com/linux/v6.14-rc5/source/lib/vsprintf.c#L1972

I've pondering for a moment about whether we should document %pC and
%pCn produce the same output or rather %pCn. I decided to try the
latter and just sent a patch to do it [0].

FYI in my case the printed value is (with both %pC and %pCn)
"32ec0000.blk-ctrl:bridge@5c".

[0] https://lore.kernel.org/20250307-vsprintf-pcn-v1-0-df0b2ccf610f@bootlin.com

Luca

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