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

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Date: Mon, 18 Mar 2024 08:27:42 +0800
From: Barry Song <21cnbao@...il.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, chris@...kel.net, 
	jcmvbkbc@...il.com, willy@...radead.org, alexghiti@...osinc.com, 
	rppt@...nel.org, dennis@...nel.org, 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] xtensa: remove redundant flush_dcache_page and
 ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE macros

On Mon, Mar 18, 2024 at 8:16 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On Wed, Mar 13, 2024 at 05:50:36PM +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. 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>



>
> Guenter