linux-kernel - Re: [PATCH] [media] tw5864: use dev_warn instead of WARN to shut up warning

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Date:   Tue, 28 Feb 2017 21:33:19 +0000
From:   Andrey Utkin <andrey.utkin@...p.bluecherry.net>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Bluecherry Maintainers <maintainers@...echerrydvr.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Hans Verkuil <hans.verkuil@...co.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrey Utkin <andrey_utkin@...tmail.com>,
        anton@...p.bluecherry.net
Subject: Re: [PATCH] [media] tw5864: use dev_warn instead of WARN to shut up
 warning

On Tue, Feb 28, 2017 at 10:14:37PM +0100, Arnd Bergmann wrote:
> tw5864_frameinterval_get() only initializes its output when it successfully
> identifies the video standard in tw5864_input. We get a warning here because
> gcc can't always track the state if initialized warnings across a WARN()
> macro, and thinks it might get used incorrectly in tw5864_s_parm:
> 
> media/pci/tw5864/tw5864-video.c: In function 'tw5864_s_parm':
> media/pci/tw5864/tw5864-video.c:816:38: error: 'time_base.numerator' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> media/pci/tw5864/tw5864-video.c:819:31: error: 'time_base.denominator' may be used uninitialized in this function [-Werror=maybe-uninitialized]
> 
> Using dev_warn() instead of WARN() avoids the __branch_check__() in
> unlikely and lets the compiler see that the initialization is correct.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Thanks for the patch.
Acked-by: Andrey Utkin <andrey.utkin@...p.bluecherry.net>

See the note below.

> ---
>  drivers/media/pci/tw5864/tw5864-video.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/pci/tw5864/tw5864-video.c b/drivers/media/pci/tw5864/tw5864-video.c
> index 9421216bb942..4d9994a11c22 100644
> --- a/drivers/media/pci/tw5864/tw5864-video.c
> +++ b/drivers/media/pci/tw5864/tw5864-video.c
> @@ -717,6 +717,8 @@ static void tw5864_frame_interval_set(struct tw5864_input *input)
>  static int tw5864_frameinterval_get(struct tw5864_input *input,
>  				    struct v4l2_fract *frameinterval)
>  {
> +	struct tw5864_dev *dev = input->root;
> +
>  	switch (input->std) {
>  	case STD_NTSC:
>  		frameinterval->numerator = 1001;
> @@ -728,8 +730,8 @@ static int tw5864_frameinterval_get(struct tw5864_input *input,
>  		frameinterval->denominator = 25;
>  		break;
>  	default:
> -		WARN(1, "tw5864_frameinterval_get requested for unknown std %d\n",
> -		     input->std);
> +	        dev_warn(&dev->pci->dev, "tw5864_frameinterval_get requested for unknown std %d\n",
> +			 input->std);
>  		return -EINVAL;
>  	}

Looks good, though, arguably, it could fit 80 columns better if you put
the string literal to separate line.