[PATCH] video: Add parentheses around VNBYTES() macro

[Miquel Raynal]

Hello,

trini at konsulko.com wrote on Tue, 19 Sep 2023 11:14:56 -0400:

> On Mon, Sep 18, 2023 at 07:04:41PM -0600, Simon Glass wrote:
> > Hi Tom, Dan,
> > 
> > On Tue, 8 Aug 2023 at 19:39, Tom Rini <trini at konsulko.com> wrote:  
> > >
> > > On Wed, Jul 26, 2023 at 09:54:08AM +0300, Dan Carpenter wrote:
> > >  
> > > > The VNBYTES() macro needs to have parentheses to prevent some (harmless)
> > > > macro expansion bugs.  The VNBYTES() macro is used like this:
> > > >
> > > >       VID_TO_PIXEL(x) * VNBYTES(vid_priv->bpix)
> > > >
> > > > The * operation is done before the / operation.  It still ends up with
> > > > the same results, but it's not ideal.
> > > >
> > > > Signed-off-by: Dan Carpenter <dan.carpenter at linaro.org>
> > > > Reviewed-by: Simon Glass <sjg at chromium.org>  
> > >
> > > In that this seems correct:
> > >
> > > Applied to u-boot/next, thanks!
> > >
> > > But I want to note that with gcc-13.1 (and binutils 2.40) or more
> > > specifically the kernel.org arm/aarch64/etc toolchains, this causes the
> > > generated code to change:
> > >    aarch64: (for 1/1 boards) all +8.0 text +8.0
> > >             bananapi-m5    : all +8 text +8
> > >                u-boot: add: 0/0, grow: 1/0 bytes: 8/0 (8)
> > >                  function                                   old     new   delta
> > >                  video_post_probe                           248     256      +8
> > >
> > > So I don't know that this was a harmless bug.  
> > 
> > Hmm I should have read the comment directly above...
> > 
> > "Note we omit the outer brackets to allow multiplication by fractional pixels."
> > 
> > Having said that, it doesn't seem to matter getting (if indeed we do)
> > a less accurate result.  
> 
> But we should fix the comment then, or decide no, this is intentional.

One year has passed and I just stumbled upon this incoherency. It would
be nice to clarify the comment or otherwise to revert Dan's patch if
judged irrelevant in the end.

Thanks!
Miquèl