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

[Guenter Roeck]

On 3/17/24 17:27, Barry Song wrote:
> On Mon, Mar 18, 2024 at 8:16 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On Wed, Mar 13, 2024 at 05:50:36PM +1300, Barry Song 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. And Huacai fixed it on LoongArch, but I found xtensa
> > > obviously has the same issue.
> >
> > Maybe I am doing something wrong, but this patch doesn't build
> > for me.
> >
> >   CC      arch/xtensa/kernel/asm-offsets.s
> > In file included from ./include/linux/highmem.h:8,
> >                   from ./include/linux/bvec.h:10,
> >                   from ./include/linux/blk_types.h:10,
> >                   from ./include/linux/writeback.h:13,
> >                   from ./include/linux/memcontrol.h:23,
> >                   from ./include/linux/swap.h:9,
> >                   from ./include/linux/suspend.h:5,
> >                   from arch/xtensa/kernel/asm-offsets.c:24:
> > ./include/linux/cacheflush.h:9:5: error: "ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE" is not defined, evaluates to 0 [-Werror=undef]
> >      9 | #if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE
>
> is it because xtensa doesn't include this at the end of
> arch/xtensa/include/asm/cacheflush.h
> while other architectures do?
>
> #include <asm-generic/cacheflush.h>

Looks like it (see my other e-mail).

Guenter