linux-kernel - Re: [PATCH v2] xtensa: remove redundant flush_dcache_page and ARCH_IMPLEMENTS_FLUSH_DCACHE

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Date: Sun, 28 Apr 2024 22:09:49 -0700
From: Max Filippov <jcmvbkbc@...il.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Barry Song <21cnbao@...il.com>, chris@...kel.net, akpm@...ux-foundation.org, 
	linux-kernel@...r.kernel.org, willy@...radead.org, dennis@...nel.org, 
	alexghiti@...osinc.com, Barry Song <v-songbaohua@...o.com>, 
	Huacai Chen <chenhuacai@...ngson.cn>, Herbert Xu <herbert@...dor.apana.org.au>, 
	kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2] xtensa: remove redundant flush_dcache_page and
 ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE macros

On Sat, Apr 27, 2024 at 12:05 PM Guenter Roeck <linux@...ck-us.net> wrote:
>
> Hi,
>
> On Tue, Mar 19, 2024 at 02:09:20PM +1300, Barry Song wrote:
> > From: Barry Song <v-songbaohua@...o.com>
> >
> > 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@...ngson.cn>
> > Cc: Herbert Xu <herbert@...dor.apana.org.au>
> > Reported-by: kernel test robot <lkp@...el.com>
> > Closes: https://lore.kernel.org/oe-kbuild-all/202403091614.NeUw5zcv-lkp@intel.com/
> > Reported-by: Barry Song <v-songbaohua@...o.com>
> > Closes: https://lore.kernel.org/all/CAGsJ_4yDk1+axbte7FKQEwD7X2oxUCFrEc9M5YOS1BobfDFXPA@mail.gmail.com/
> > Reported-by: Guenter Roeck <linux@...ck-us.net>
> > Closes: https://lore.kernel.org/all/aaa8b7d7-5abe-47bf-93f6-407942436472@roeck-us.net/
> > Fixes: 77292bb8ca69 ("crypto: scomp - remove memcpy if sg_nents is 1 and pages are lowmem")
> > Signed-off-by: Barry Song <v-songbaohua@...o.com>
>
> The mainline kernel still fails to build xtensa:allmodconfig.
>
> Building xtensa:allmodconfig ... failed
> --------------
> Error log:
> crypto/scompress.c: In function 'scomp_acomp_comp_decomp':
> crypto/scompress.c:174:38: error: unused variable 'dst_page' [-Werror=unused-variable]
>   174 |                         struct page *dst_page = sg_page(req->dst);
>
> This patch fixes the problem. Is there a chance to get it applied to the
> upstream kernel, or should I just stop build testing xtensa:allmodconfig ?

Applied to my xtensa tree.
I was still hoping to see rationale for why this is a useful warning.

-- 
Thanks.
-- Max