linux-kernel - Re: [PATCH] media: saa6588: Fix unsafe debug printk macro

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Message-ID: <958a157f-e01d-499c-9f3e-d19e33b1de74@kernel.org>
Date: Mon, 13 Oct 2025 12:35:38 +0200
From: Hans Verkuil <hverkuil+cisco@...nel.org>
To: Shrikant Raskar <raskar.shree97@...il.com>, hverkuil@...nel.org,
 mchehab@...nel.org
Cc: linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: saa6588: Fix unsafe debug printk macro

On 23/09/2025 19:59, Shrikant Raskar wrote:
> The existing dprintk macro used an unwrapped `if` statement, which can lead
> to logic errors when used in if/else constructs. This patch wraps the macro
> in a do { } while (0) block to ensure safe usage.
> 
> This change resolves the following checkpatch error:
> ERROR: Macros starting with if should be enclosed by a do - while loop to
> avoid possible if/else logic defects
> 
> Signed-off-by: Shrikant Raskar <raskar.shree97@...il.com>
> ---
>  drivers/media/i2c/saa6588.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/i2c/saa6588.c b/drivers/media/i2c/saa6588.c
> index fb09e4560d8a..71d34d229564 100644
> --- a/drivers/media/i2c/saa6588.c
> +++ b/drivers/media/i2c/saa6588.c
> @@ -50,7 +50,7 @@ MODULE_LICENSE("GPL");
>  
>  #define UNSET       (-1U)
>  #define PREFIX      "saa6588: "
> -#define dprintk     if (debug) printk
> +#define dprintk(fmt, args...)  do { if (debug) printk(fmt, ##args); } while (0)
>  
>  struct saa6588 {
>  	struct v4l2_subdev sd;

I think we can do better than this.

Looking at how dprintk is used in this driver, I see that in almost all cases
it is preceded by a 'if (debug > X)' condition. Except for one occurrence in
saa6588_configure().

So I would propose to just drop dprintk, and instead change dprintk to
pr_info and pr_cont. And add a 'if (debug)' in saa6588_configure().

Actually, v4l2_info(&s->sd, ...) would be even better, then the PREFIX can
be dropped as well.

Regards,

	Hans