linux-kernel - Re: [PATCH] media: rkvdec: silence ktest bot build warning

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Date:   Thu, 7 Jan 2021 12:41:32 +0100
From:   Boris Brezillon <boris.brezillon@...labora.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Adrian Ratiu <adrian.ratiu@...labora.com>,
        linux-media@...r.kernel.org, kernel@...labora.com,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH] media: rkvdec: silence ktest bot build warning

On Thu, 7 Jan 2021 10:13:43 +0100
Hans Verkuil <hverkuil@...all.nl> wrote:

> On 08/12/2020 16:55, Adrian Ratiu wrote:
> > Some configurations built by the ktest bot produce the following
> > warn, so mark the struct as __maybe_unused to avoid unnecessary
> > ML spam.
> >   
> >>> drivers/staging/media/rkvdec/rkvdec.c:967:34: warning: unused variable 'of_rkvdec_match' [-Wunused-const-variable]  
> >    static const struct of_device_id of_rkvdec_match[] = {
> > 				    ^
> >    1 warning generated.  
> 
> I suspect that this is because there is no 'depends on OF' in the Kconfig.
> 
> '__maybe_unused' isn't used for this anywhere else, so this does not seem like the
> right approach.

It's not uncommon to do that, especially when you want the driver to be
compile-tested (`git grep -C2 __maybe_unused|grep of_device_id` even
reports 2 drivers in the media tree :P). A `depends on OF` or an
`#ifdef CONFIG_OF` section surrounding the of_rkvdec_match declaration
would also do the trick.

> 
> Regards,
> 
> 	Hans
> 
> > 
> > vim +/of_rkvdec_match +967 drivers/staging/media/rkvdec/rkvdec.c
> > 
> >    966  
> >  > 967	static const struct of_device_id of_rkvdec_match[] = {  
> >    968		{ .compatible = "rockchip,rk3399-vdec" },
> >    969		{ /* sentinel */ }
> >    970	};
> >    971	MODULE_DEVICE_TABLE(of, of_rkvdec_match);
> >    972
> > 
> > Cc: Boris Brezillon <boris.brezillon@...labora.com>
> > Cc: Ezequiel Garcia <ezequiel@...labora.com>
> > Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
> > Reported-by: kernel test robot <lkp@...el.com>
> > Signed-off-by: Adrian Ratiu <adrian.ratiu@...labora.com>
> > ---
> >  drivers/staging/media/rkvdec/rkvdec.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/staging/media/rkvdec/rkvdec.c b/drivers/staging/media/rkvdec/rkvdec.c
> > index aa4f8c287618..3af0f02ec59b 100644
> > --- a/drivers/staging/media/rkvdec/rkvdec.c
> > +++ b/drivers/staging/media/rkvdec/rkvdec.c
> > @@ -992,7 +992,7 @@ static void rkvdec_watchdog_func(struct work_struct *work)
> >  	}
> >  }
> >  
> > -static const struct of_device_id of_rkvdec_match[] = {
> > +static const struct of_device_id __maybe_unused of_rkvdec_match[] = {
> >  	{ .compatible = "rockchip,rk3399-vdec" },
> >  	{ /* sentinel */ }
> >  };
> >   
>