On Tue, May 11, 2010 at 17:53, Dmitry Torokhov wrote: > On Tue, May 11, 2010 at 11:48:36PM +0200, Johannes Weiner wrote: >> On Tue, May 11, 2010 at 04:54:41PM -0400, Mike Frysinger wrote: >> > does the phrase "DMA safe buffer" imply cache alignment ? >> >> I guess that depends on the architectural requirements. On x86, >> apparently, not so much. On ARM, probably yes, as it's the >> requirement to properly maintain coherency. > > It looks liek ARM (and a few others) do this: > > [dtor@hammer work]$ grep -r ARCH_KMALLOC_MINALIGN arch/ > arch/sh/include/asm/page.h:#define ARCH_KMALLOC_MINALIGN L1_CACHE_BYTES > arch/frv/include/asm/mem-layout.h:#define ARCH_KMALLOC_MINALIGN 8 > arch/powerpc/include/asm/page_32.h:#define ARCH_KMALLOC_MINALIGN L1_CACHE_BYTES > arch/arm/include/asm/cache.h:#define ARCH_KMALLOC_MINALIGN L1_CACHE_BYTES > arch/microblaze/include/asm/page.h:#define ARCH_KMALLOC_MINALIGN L1_CACHE_BYTES > arch/mips/include/asm/mach-tx49xx/kmalloc.h: * All happy, no need to define ARCH_KMALLOC_MINALIGN > arch/mips/include/asm/mach-ip27/kmalloc.h: * All happy, no need to define ARCH_KMALLOC_MINALIGN > arch/mips/include/asm/mach-ip32/kmalloc.h:#define ARCH_KMALLOC_MINALIGN 32 > arch/mips/include/asm/mach-ip32/kmalloc.h:#define ARCH_KMALLOC_MINALIGN 128 > arch/mips/include/asm/mach-generic/kmalloc.h:#define ARCH_KMALLOC_MINALIGN 128 > arch/avr32/include/asm/cache.h:#define ARCH_KMALLOC_MINALIGN L1_CACHE_BYTES if ARCH_KMALLOC_MINALIGN is not defined, the current allocators default to: slub - alignof(unsigned long long) slab - alignof(unsigned long long) slob - alignof(unsigned long) which for many arches can mean an alignment of merely 4 or 8 lets look at the cacheline sizes for arches that dont set ARCH_KMALLOC_MINALIGN to L1_CACHE_BYTES: - alplha - 32 or 64 - frv - 32 or 64 - blackfin - 32 - parisc - 32 or 64 - mn10300 - 16 - s390 - 256 - score - 16 - sparc - 32 - xtensa - 16 or 32 assuming alpha and s390 handle cache coherency in hardware, it looks to me like the proposed assumption (kmalloc returns cachealigned pointers when cache management is in software) does not hold true. so should these other arches also be setting ARCH_KMALLOC_MINALIGN to L1_CACHE_BYTES ? -mike -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
