Re: [PATCH -next 1/3] staging: vt6655: remove unused variable

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Mar 15, 2021 at 07:46:35PM -0600, Edmundo Carmona Antoranz wrote:
> On Sun, Mar 14, 2021 at 10:01 AM Greg KH <gregkh@linuxfoundation.org> wrote:
> >
> > > -                     byData = inb(0x61);                     \
> > > +                     inb(0x61);                              \
> >
> > Are you sure that the compiler does not make the inb() now go away?
> 
> Hey, Greg!
> 
> Take what you are about to read with a BIG grain of salt because I'm
> just learning about the details of what's going on and the tools at my
> disposal.
> 
> On v5.11 with an allyesconfig, by changing the value of
> CB_DELAY_LOOP_WAIT in mac.h to 100 to force the compiler to include
> the `else` path that includes the for with the inb() call, comparing
> the resulting srom.o files before/after the patch:
> 
> Compiling with only the value in mac.h changed:
> 
> $ size drivers/staging/vt6655/srom.o
>   text    data     bss     dec     hex filename
>    959       0       0     959     3bf drivers/staging/vt6655/srom.o
> 
> By removing the variable in the macro:
> 
> $ size drivers/staging/vt6655/srom.o
>   text    data     bss     dec     hex filename
>    959       0       0     959     3bf drivers/staging/vt6655/srom.o
> 
> By also removing the inb() call, in other words, keeping an empty for:
> 
> $ size drivers/staging/vt6655/srom.o
>   text    data     bss     dec     hex filename
>    865       0       0     865     361 drivers/staging/vt6655/srom.
> 
> 
> That being the case, I think that inb is not fading away by removing
> the variable... at least in my environment.
> 
> Just in case, it's not like I _want_ the patch to be accepted. I took
> it as an exercise and if you think that you want to play safe and
> reject it, it's fine. It was still valuable to me because of your
> question about the function going away and me trying to find out.

Ok, I'll leave this as-is because the inb() needs to happen, so saving
the value is normal for stuff like this.

thanks,

greg k-h