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

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Date: Sun, 17 Mar 2024 17:34:31 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Barry Song <21cnbao@...il.com>
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 3/17/24 17:27, Barry Song wrote:
> 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>
> 

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

Guenter