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Fri, 30 Oct 2026 09:29:38 +0100 (CET) From: Julian Vetter To: Russell King Cc: Linus Walleij , Arnd Bergmann , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Julian Vetter Subject: [PATCH] ARM: fix big-endian check for IO memcpy and memset Date: Fri, 30 Oct 2026 09:29:32 +0100 Message-ID: <20261030082932.193164-1-julian@outer-limits.org> X-Mailer: git-send-email 2.53.0 X-Archived-By: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20261030_012948_744937_48B5811C X-CRM114-Status: GOOD ( 17.57 ) X-Spam-Score: -2.1 (--) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" X-Spam-Status: No, score=-16.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_EF,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 The commit 7ddfe625cbc1 ("ARM: optimize memset_io()/memcpy_fromio()/memcpy_toio()") switched little-endian builds to mmioset()/mmiocpy() and intended to keep the byte-wise _memset_io()/_memcpy_fromio()/_memcpy_toio() for big-endian builds. However, the check uses __ARMBE__, which is not defined by GCC. The define used throughout the kernel is __ARMEB__ for big-endian ARM. So, big-endian builds have been using mmioset() and mmiocpy() ever since. This is a problem on ARMv5 BE32 platforms like IXP4xx, where word accesses to IO memory can end up on different byte lanes than byte accesses. Fix the typo, so big-endian builds use the correct byte-wise implementations again, as originally intended. Switching big-endian builds to the generic implementation from lib/iomem_copy.c instead is not an option either, because it also uses word accesses for the aligned parts of a buffer and thus has the same byte lane problem on BE32. ARMv6/v7 BE8 mode would work with both, but it is marked as broken and is expected to be removed, so it is not worth treating it differently from BE32. Signed-off-by: Julian Vetter --- This replaces my earlier patch that removed the byte-wise helpers: https://lore.kernel.org/all/20241203083838.3260036-1-jvetter@outer-limits.org/ I have done a compilation test with ixp4xx_defconfig and see that drivers/pci/pci-sysfs.o and drivers/mtd/maps/map_funcs.o now call _memcpy_fromio()/_memcpy_toio() instead of mmiocpy(). This is however untested on hardware. I think the problem didn't show up on Linus' hw test, because platform doesn't use those drivers. --- arch/arm/include/asm/io.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h index e6bd9e79737c..50e142f817f5 100644 --- a/arch/arm/include/asm/io.h +++ b/arch/arm/include/asm/io.h @@ -308,7 +308,7 @@ extern void _memset_io(volatile void __iomem *, int, size_t); #define writesw(p,d,l) __raw_writesw(p,d,l) #define writesl(p,d,l) __raw_writesl(p,d,l) -#ifndef __ARMBE__ +#ifndef __ARMEB__ static inline void memset_io(volatile void __iomem *dst, unsigned c, size_t count) { -- 2.53.0