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

[Guenter Roeck]

On 3/18/24 19:16, Barry Song wrote:
> On Tue, Mar 19, 2024 at 3:12 PM Max Filippov <jcmvbkbc@xxxxxxxxx> wrote:
> > On Mon, Mar 18, 2024 at 6:27 PM Barry Song <21cnbao@xxxxxxxxx> 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.
> >
> > I wonder why this warning is considered useful in the first place?
>
> Guenter reported it as an error not a warning
> "
>
> Error log:
> crypto/scompress.c: In function 'scomp_acomp_comp_decomp':
> crypto/scompress.c:174:38: error: unused variable 'dst_page'"
>
> is it because xtensa's toolchain is different with others?

It is because -Werror is now default in allmodconfig builds.
Other test build systems may manually override that.

Guenter