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

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Message-ID:
 <TY3PR01MB11346E57A3DF8D8A90A405E4686812@TY3PR01MB11346.jpnprd01.prod.outlook.com>
Date: Mon, 28 Apr 2025 11:36:08 +0000
From: Biju Das <biju.das.jz@...renesas.com>
To: "Lad, Prabhakar" <prabhakar.csengg@...il.com>, laurent.pinchart
	<laurent.pinchart@...asonboard.com>
CC: Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil
	<hverkuil@...all.nl>, "linux-media@...r.kernel.org"
	<linux-media@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "linux-renesas-soc@...r.kernel.org"
	<linux-renesas-soc@...r.kernel.org>, Fabrizio Castro
	<fabrizio.castro.jz@...esas.com>, Tommaso Merciai
	<tommaso.merciai.xr@...renesas.com>, Prabhakar Mahadev Lad
	<prabhakar.mahadev-lad.rj@...renesas.com>, Dan Carpenter
	<dan.carpenter@...aro.org>
Subject: RE: [PATCH] media: renesas: rzg2l-cru: Simplify FIFO empty check



> -----Original Message-----
> From: Lad, Prabhakar <prabhakar.csengg@...il.com>
> Sent: 28 April 2025 12:33
> 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().

Looks a typo rz3e_fifo_empty()->rzg3e_fifo_empty(). Above as well.

Cheers,
Biju