Messages in this thread Patch in this message | | | Date | Thu, 5 Nov 2020 08:36:26 +0000 | From | Lee Jones <> | Subject | Re: [PATCH 34/36] tty: serial: pmac_zilog: Make disposable variable __always_unused |
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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@linuxfoundation.org> > > > Cc: Jiri Slaby <jirislaby@kernel.org> > > > Cc: Michael Ellerman <mpe@ellerman.id.au> > > > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> > > > Cc: Paul Mackerras <paulus@samba.org> > > > Cc: linux-serial@vger.kernel.org > > > Cc: linuxppc-dev@lists.ozlabs.org > > > Signed-off-by: Lee Jones <lee.jones@linaro.org> > > > --- > > > 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 Follow Linaro: Facebook | Twitter | Blog
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