Re: [PATCH 34/36] tty: serial: pmac_zilog: Make disposable variable __always_unused

[Jiri Slaby]

On 05. 11. 20, 8:04, Christophe Leroy wrote:
> Le 04/11/2020 à 20:35, Lee Jones a écrit :
> > Fixes the following W=1 kernel build warning(s):
> >
> >   drivers/tty/serial/pmac_zilog.h:365:58: warning: variable ‘garbage’ 
> > set but not used [-Wunused-but-set-variable]
>
> Explain how you are fixing this warning.
>
> Setting  __always_unused is usually not the good solution for fixing 
> this warning, but here I guess this is likely the good solution. But it 
> should be explained why.

Or, why is the "garbage =" needed in the first place? read_zsdata is not 
defined with __warn_unused_result__. And even if it was, would 
(void)!read_zsdata(port) fix it?

> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Jiri Slaby <jirislaby@xxxxxxxxxx>
> > Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> > Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Paul Mackerras <paulus@xxxxxxxxx>
> > Cc: linux-serial@xxxxxxxxxxxxxxx
> > Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > ---
> >   drivers/tty/serial/pmac_zilog.h | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/serial/pmac_zilog.h 
> > b/drivers/tty/serial/pmac_zilog.h
> > index bb874e76810e0..968aec7c1cf82 100644
> > --- a/drivers/tty/serial/pmac_zilog.h
> > +++ b/drivers/tty/serial/pmac_zilog.h
> > @@ -362,7 +362,7 @@ static inline void zssync(struct uart_pmac_port 
> > *port)
> >   /* Misc macros */
> >   #define ZS_CLEARERR(port)    (write_zsreg(port, 0, ERR_RES))
> > -#define ZS_CLEARFIFO(port)   do { volatile unsigned char garbage; \
> > +#define ZS_CLEARFIFO(port)   do { volatile unsigned char 
> > __always_unused garbage; \
> >                        garbage = read_zsdata(port); \
> >                        garbage = read_zsdata(port); \
> >                        garbage = read_zsdata(port); \

thanks,
--
js