linux-kernel - Re: (EXT) Re: [PATCH 4/8] media: imx: Fail conversion if pixel format not supported

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Date:   Mon, 07 Feb 2022 10:52:00 +0100
From:   Alexander Stein <alexander.stein@...tq-group.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Dorota Czaplejewicz <dorota.czaplejewicz@...i.sm>
Cc:     Steve Longerbeam <slongerbeam@...il.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Rui Miguel Silva <rmfrfs@...il.com>,
        linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: (EXT) Re: [PATCH 4/8] media: imx: Fail conversion if pixel format not supported

Hi Laurent and Dorota,

Am Samstag, 5. Februar 2022, 08:51:51 CET schrieb Dorota Czaplejewicz:
> * PGP Signed by an unknown key
> 
> Hi Laurent,
> 
> On Sat, 5 Feb 2022 06:07:37 +0200
> 
> Laurent Pinchart <laurent.pinchart@...asonboard.com> wrote:
> > Hi Alexander and Dorota,
> > 
> > Thank you for the patch.
> > 
> > On Fri, Feb 04, 2022 at 01:15:10PM +0100, Alexander Stein wrote:
> > > From: Dorota Czaplejewicz <dorota.czaplejewicz@...i.sm>
> > > 
> > > imx_media_find_mbus_format has NULL as a valid return value,
> > > therefore the caller should take it into account.
> > > 
> > > Signed-off-by: Dorota Czaplejewicz <dorota.czaplejewicz@...i.sm>
> > > Signed-off-by: Alexander Stein <alexander.stein@...tq-group.com>
> > > ---
> > > 
> > >  drivers/staging/media/imx/imx-media-utils.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/drivers/staging/media/imx/imx-media-utils.c
> > > b/drivers/staging/media/imx/imx-media-utils.c index
> > > 32aaa2e81bea..e0a256a08c3b 100644
> > > --- a/drivers/staging/media/imx/imx-media-utils.c
> > > +++ b/drivers/staging/media/imx/imx-media-utils.c
> > > @@ -544,6 +544,9 @@ static int imx56_media_mbus_fmt_to_pix_fmt(struct
> > > v4l2_pix_format *pix,> > 
> > >  		cc = imx_media_find_mbus_format(code, PIXFMT_SEL_YUV);
> > 
> > The code passed to the function comes from the previous line:
> > 	imx_media_enum_mbus_formats(&code, 0, PIXFMT_SEL_YUV);
> > 
> > As far as I can tell, this is guaranteed to return a code that will
> > result in imx_media_find_mbus_format() returning a non-NULL pointer.
> 
> While I am not well-versed in the implicit code style of the kernel, I
> decided to leave it in because it makes the code more locally legible. With
> a check here, even a non-functional one, there's no need to understand the
> internals of `imx_media_find_mbus_format` that are only implicit. That
> makes the code less surprising when interested only in the outer function.
> 
> The other advantage of a check is becoming robust against future changes to
> `imx_media_find_mbus_format` itself.
> 
> I don't have a strong preference about keeping or leaving this patch, but if
> this check was there in the first place, I wouldn't have spent time trying
> to figure out whether there's a bug here.

Laurent, thanks for your feedback.
I'm on Dorota's side here. While you are right that the code from 
  imx_media_enum_mbus_formats(&code, 0, PIXFMT_SEL_YUV);
is guaranteed to return something. I don't lnek this implicit assumption over 
2 function calls. Better be safe than sorry. For that reason code should be 
initialized as well. Will create a patch for that.

Regards,
Alexander