Re: [PATCH v2] xtensa: remove redundant flush_dcache_page and ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE macros

[Guenter Roeck]

On 3/18/24 18:27, Barry Song wrote:
> On Tue, Mar 19, 2024 at 2:09 PM Barry Song <21cnbao@xxxxxxxxx> wrote:
> > From: Barry Song <v-songbaohua@xxxxxxxx>
> >
> > xtensa's flush_dcache_page() can be a no-op sometimes. There is a
> > generic implementation for this case in include/asm-generic/
> > cacheflush.h.
> >   #ifndef ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
> >   static inline void flush_dcache_page(struct page *page)
> >   {
> >   }
> >
> >   #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 0
> >   #endif
> >
> > So remove the superfluous flush_dcache_page() definition, which also
> > helps silence potential build warnings complaining the page variable
> > passed to flush_dcache_page() is not used.
> >
> >     In file included from crypto/scompress.c:12:
> >     include/crypto/scatterwalk.h: In function 'scatterwalk_pagedone':
> >     include/crypto/scatterwalk.h:76:30: warning: variable 'page' set but not used [-Wunused-but-set-variable]
> >        76 |                 struct page *page;
> >           |                              ^~~~
> >     crypto/scompress.c: In function 'scomp_acomp_comp_decomp':
> > > > crypto/scompress.c:174:38: warning: unused variable 'dst_page' [-Wunused-variable]
> >       174 |                         struct page *dst_page = sg_page(req->dst);
> >           |
> >
> > The issue was originally reported on LoongArch by kernel test
> > robot (Huacai fixed it on LoongArch), then reported by Guenter
> > and me on xtensa.
> >
> > This patch also removes lots of redundant macros which have
> > been defined by asm-generic/cacheflush.h.
> >
> > Cc: Huacai Chen <chenhuacai@xxxxxxxxxxx>
> > Cc: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202403091614.NeUw5zcv-lkp@xxxxxxxxx/
> > Reported-by: Barry Song <v-songbaohua@xxxxxxxx>
> > Closes: https://lore.kernel.org/all/CAGsJ_4yDk1+axbte7FKQEwD7X2oxUCFrEc9M5YOS1BobfDFXPA@xxxxxxxxxxxxxx/
> > Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
>
> Hi Guenter,
> I am not a xtensa guy, so I will need your help for a full test. if
> turns out it is a too big(ambitious)

I sent a Tested-by: tag to your patch. As far as my testing goes, it works fine,
and I added your patch to my "testing" branch (which tries to be buildable
and testable for all architectures).

> fix, a minimal fix might be:

FWIW, I think a minimal fix would have been to mark the variable as __maybe_unused,
but as others have pointed out it would be nice if there would be a guidance
about optional API functions like this one that specifies if it may be
implemented as macro and, if so, how it has to handle unused variables.

Thanks,
Guenter