linux-kernel - Re: [PATCH] media: renesas: rzg2l-cru: Simplify FIFO empty check

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Message-ID: <CA+V-a8vDDLZ422nZds7pEEW+gZ1n7s-U3eJjmG8DsOJT9uJygQ@mail.gmail.com>
Date: Mon, 28 Apr 2025 12:32:59 +0100
From: "Lad, Prabhakar" <prabhakar.csengg@...il.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil <hverkuil@...all.nl>, linux-media@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-renesas-soc@...r.kernel.org, 
	Biju Das <biju.das.jz@...renesas.com>, 
	Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 
	Tommaso Merciai <tommaso.merciai.xr@...renesas.com>, 
	Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>, 
	Dan Carpenter <dan.carpenter@...aro.org>
Subject: Re: [PATCH] media: renesas: rzg2l-cru: Simplify FIFO empty check

Hi Laurent,

On Mon, Apr 28, 2025 at 12:25 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
>
> On Mon, Apr 28, 2025 at 12:17:54PM +0100, Lad, Prabhakar wrote:
> > On Mon, Apr 28, 2025 at 10:59 AM Laurent Pinchart wrote:
> > > On Mon, Apr 28, 2025 at 10:52:08AM +0100, Prabhakar wrote:
> > > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > >
> > > > Simplify the `rzg2l_fifo_empty()` helper by removing the redundant
> > > > comparison in the return path. Now the function explicitly returns `true`
> > > > if the FIFO write and read pointers match, and `false` otherwise, improving
> > > > readability without changing behavior.
> > > >
> > > > Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
> > > > Closes: https://lore.kernel.org/all/aAtQThCibZCROETx@stanley.mountain/
> > > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > > ---
> > > >  drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c b/drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c
> > > > index 067c6af14e95..97faefcd6019 100644
> > > > --- a/drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c
> > > > +++ b/drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c
> > > > @@ -348,7 +348,7 @@ bool rzg2l_fifo_empty(struct rzg2l_cru_dev *cru)
> > > >       if (amnfifopntr_w == amnfifopntr_r_y)
> > > >               return true;
> > > >
> > > > -     return amnfifopntr_w == amnfifopntr_r_y;
> > > > +     return false;
> > >
> > > So the function always returned true. This seems to be a bug fix, please
> > > add a Fixes: tag. The commit message should also make it clear that
> > > you're fixing an issue, not just simplifying the code.
> >
> > No, the function returned true only if the pointers matched;
> > otherwise, amnfifopntr_w == amnfifopntr_r_y would return false. I was
> > simply removing the repetitive pointer check and directly returning
> > false at the end of the function, as we can be certain at that point.
> > Hence, I did not add a Fixes tag. Am I missing something?
>
> Oops, you're right, my bad.
>
> > > Personally I'd have written
> > >
> > > diff --git a/drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c b/drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c
> > > index 067c6af14e95..3d0810b3c35e 100644
> > > --- a/drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c
> > > +++ b/drivers/media/platform/renesas/rzg2l-cru/rzg2l-video.c
> > > @@ -345,8 +345,6 @@ bool rzg2l_fifo_empty(struct rzg2l_cru_dev *cru)
> > >         amnfifopntr_w = amnfifopntr & AMnFIFOPNTR_FIFOWPNTR;
> > >         amnfifopntr_r_y =
> > >                 (amnfifopntr & AMnFIFOPNTR_FIFORPNTR_Y) >> 16;
> > > -       if (amnfifopntr_w == amnfifopntr_r_y)
> > > -               return true;
> > >
> > >         return amnfifopntr_w == amnfifopntr_r_y;
> > >  }
> > >
> > > but that's also a bit of a style preference.
> >
> > I wanted to keep this consistent with the rz3e_fifo_empty(). If you
> > prefer the above I'll do that in v2.
>
> Up to you.
>
Thanks. OK, let's keep this patch as is to stay consistent with
rz3e_fifo_empty().

Cheers,
Prabhakar