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

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Message-ID: <CAHc1_P5+xz5JK=dHQGBOt_kfCyeAm6mcX2zbjgE0WtR5mnDqdg@mail.gmail.com>
Date: Fri, 24 Oct 2025 17:15:24 +0530
From: Shrikant <raskar.shree97@...il.com>
To: Hans Verkuil <hverkuil+cisco@...nel.org>
Cc: hverkuil@...nel.org, mchehab@...nel.org, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: saa6588: Fix unsafe debug printk macro

On Mon, Oct 13, 2025 at 4:05 PM Hans Verkuil <hverkuil+cisco@...nel.org> wrote:
>
> 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.
Thank you so much for reviewing my patch and sharing your feedback.
I will drop the dprintk macro and will use the v4l2_info() helper as
you suggested. I will share the v2 patch shortly.

Regards,
Shrikant