Received-SPF: pass (google.com: domain of linux-kernel+bounces-107635-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Sender: Guenter Roeck <groeck7@gmail.com>
Message-ID: <ce352c9c-2052-4a23-809a-ef4cc9b7169c@roeck-us.net>
Date: Tue, 19 Mar 2024 07:17:58 -0700
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v2] xtensa: remove redundant flush_dcache_page and
 ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE macros
Content-Language: en-US
To: Barry Song <21cnbao@gmail.com>, chris@zankel.net, jcmvbkbc@gmail.com,
 akpm@linux-foundation.org, linux-kernel@vger.kernel.org
Cc: willy@infradead.org, dennis@kernel.org, alexghiti@rivosinc.com,
 Barry Song <v-songbaohua@oppo.com>, Huacai Chen <chenhuacai@loongson.cn>,
 Herbert Xu <herbert@gondor.apana.org.au>, kernel test robot <lkp@intel.com>
References: <20240319010920.125192-1-21cnbao@gmail.com>
 <CAGsJ_4z1k9BQGPJvuXtXPQueokM-yu0nf7yQko6yjhj-0fgAnA@mail.gmail.com>
From: Guenter Roeck <linux@roeck-us.net>
Autocrypt: addr=linux@roeck-us.net; keydata=
 xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN
 RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7
 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl
 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh
 gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX
 IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC
 kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0
 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s
 jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk
 BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv
 ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL
 CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA
 nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx
 hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1
 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9
 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu
 GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI
 sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT
 Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l
 HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8
 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA
 l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq
 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7
 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM
 J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi
 pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz
 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w
 ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF
 I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT
 nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY
 HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX
 JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+
 J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW
 cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG
 wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh
 hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H
 nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng
 QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj
 trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk
 WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI
 HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU
 mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q=
In-Reply-To: <CAGsJ_4z1k9BQGPJvuXtXPQueokM-yu0nf7yQko6yjhj-0fgAnA@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit

On 3/18/24 18:27, Barry Song wrote:
> On Tue, Mar 19, 2024 at 2:09 PM Barry Song <21cnbao@gmail.com> wrote:
>>
>> From: Barry Song <v-songbaohua@oppo.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@loongson.cn>
>> Cc: Herbert Xu <herbert@gondor.apana.org.au>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Closes: https://lore.kernel.org/oe-kbuild-all/202403091614.NeUw5zcv-lkp@intel.com/
>> Reported-by: Barry Song <v-songbaohua@oppo.com>
>> Closes: https://lore.kernel.org/all/CAGsJ_4yDk1+axbte7FKQEwD7X2oxUCFrEc9M5YOS1BobfDFXPA@mail.gmail.com/
>> Reported-by: Guenter Roeck <linux@roeck-us.net>
> 
> Hi Guenter,
> I am not a xtensa guy, so I will need your help for a full test. if
> turns out it is a too big(ambitious)

I sent a Tested-by: tag to your patch. As far as my testing goes, it works fine,
and I added your patch to my "testing" branch (which tries to be buildable
and testable for all architectures).

> fix, a minimal fix might be:
> 

FWIW, I think a minimal fix would have been to mark the variable as __maybe_unused,
but as others have pointed out it would be nice if there would be a guidance
about optional API functions like this one that specifies if it may be
implemented as macro and, if so, how it has to handle unused variables.

Thanks,
Guenter