linux-kernel - Re: [PATCH] dma: ste_dma40: fix unneeded variable warning

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Date:   Fri, 12 Jul 2019 22:32:05 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Vinod Koul <vkoul@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        dmaengine@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] dma: ste_dma40: fix unneeded variable warning

On Fri, Jul 12, 2019 at 9:17 PM 'Nick Desaulniers' via Clang Built
Linux <clang-built-linux@...glegroups.com> wrote:
>
> On Fri, Jul 12, 2019 at 10:39 AM Nathan Chancellor
> <natechancellor@...il.com> wrote:
> >
> > On Fri, Jul 12, 2019 at 11:13:30AM +0200, Arnd Bergmann wrote:
> > > clang-9 points out that there are two variables that depending on the
> > > configuration may only be used in an ARRAY_SIZE() expression but not
> > > referenced:
> > >
> > > drivers/dma/ste_dma40.c:145:12: error: variable 'd40_backup_regs' is not needed and will not be emitted [-Werror,-Wunneeded-internal-declaration]
> > > static u32 d40_backup_regs[] = {
> > >            ^
> > > drivers/dma/ste_dma40.c:214:12: error: variable 'd40_backup_regs_chan' is not needed and will not be emitted [-Werror,-Wunneeded-internal-declaration]
> > > static u32 d40_backup_regs_chan[] = {
> > >
> > > Mark these __maybe_unused to shut up the warning.
> > >
> > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
>
> Thanks for the patch!
>
> >
> > Might be worth mentioning that this warning will only appear when
> > CONFIG_PM is unset (they are both used in d40_save_restore_registers).
>
> So would moving the definition into a
> #ifdef CONFIG_PM
> #endif
> block be better than __maybe_unused?
>

That would not work here, since the driver still uses ARRAY_SIZE() on
the variable.
Even more #ifdefs could solve that as well, but I don't want to spend too much
effort on this driver since it has almost no users.

      Arnd