Messages in this thread | | | Date | Mon, 29 Apr 2024 06:58:10 -0700 | Subject | Re: [PATCH v2] xtensa: remove redundant flush_dcache_page and ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE macros | From | Guenter Roeck <> |
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On 4/28/24 22:09, Max Filippov wrote: > On Sat, Apr 27, 2024 at 12:05 PM Guenter Roeck <linux@roeck-us.net> wrote: >> >> Hi, >> >> On Tue, Mar 19, 2024 at 02:09:20PM +1300, Barry Song 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> >>> 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@oppo.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. >
Useful in general or here ? In general it helps a lot to identify unnecessary or buggy code, and I think it is very useful. In this case, the other option would have been to declare the variable as __maybe_unused. I think that has been discussed. Personally I preferred the more comprehensive patch because it makes the code more generic, but at this point in the release cycle I really only want to know what to do with xtensa:allmodconfig test builds.
Thanks, Guenter
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