On Thu, 05 Nov 2020, Jiri Slaby wrote:
> 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.
There are normally 3 ways to fix this warning;
- Start using/checking the variable/result
- Remove the variable
- Mark it as __{always,maybe}_unused
The later just tells the compiler that not checking the resultant
value is intentional. There are some functions (as Jiri mentions
below) which are marked as '__must_check' which *require* a dummy
(garbage) variable to be used.
> Or, why is the "garbage =" needed in the first place? read_zsdata is not
> defined with __warn_unused_result__.
I used '__always_used' here for fear of breaking something.
However, if it's safe to remove it, then all the better.
> And even if it was, would (void)!read_zsdata(port) fix it?
That's hideous. :D
*Much* better to just use '__always_used' in that use-case.
> > > 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,
--
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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