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Date: Wed, 3 Mar 2010 08:54:45 +0900 From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> To: linuxppc-dev@...abs.org Cc: benh@...nel.crashing.or, arnd@...db.de, davem@...emloft.net, linux-kernel@...r.kernel.org Subject: [PATCH] powerpc: remove IOMMU_VMERGE config option Seems that IOMMU_VMERGE option description gives the false information: http://marc.info/?l=linux-sparc&m=126753808727669&w=2 http://marc.info/?l=linux-sparc&m=126753880528825&w=2 IOMMU_VMERGE is unnecessary nowadays so how about removing it? = From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> Subject: [PATCH] powerpc: remove IOMMU_VMERGE config option The description says: Cause IO segments sent to a device for DMA to be merged virtually by the IOMMU when they happen to have been allocated contiguously. This doesn't add pressure to the IOMMU allocator. However, some drivers don't support getting large merged segments coming back from *_map_sg(). Most drivers don't have this problem; it is safe to say Y here. It's out of date. Long ago, drivers didn't have a way to tell IOMMUs about their segment length limit (that is, the maximum segment length that they can handle). So IOMMUs merged as many segments as possible and gave too large segments to drivers. dma_get_max_seg_size() was introduced to solve the above problem. Device drives can use the API to tell IOMMU about the maximum segment length that they can handle. The powerpc IOMMU supports dma_get_max_seg_size() properly. In addition, the default limit (64K) should be safe for everyone. So this config option seems to be unnecessary. Note that this config option just enables users to disable the virtual merging by default (powerpc enables it by default). Users can still disable the virtual merging by the boot parameter. Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> --- arch/powerpc/Kconfig | 11 +---------- 1 files changed, 1 insertions(+), 10 deletions(-) diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig index 155d571..2dfa83b 100644 --- a/arch/powerpc/Kconfig +++ b/arch/powerpc/Kconfig @@ -314,17 +314,8 @@ config 8XX_MINIMAL_FPEMU It is recommended that you build a soft-float userspace instead. config IOMMU_VMERGE - bool "Enable IOMMU virtual merging" + def_bool y depends on PPC64 - default y - help - Cause IO segments sent to a device for DMA to be merged virtually - by the IOMMU when they happen to have been allocated contiguously. - This doesn't add pressure to the IOMMU allocator. However, some - drivers don't support getting large merged segments coming back - from *_map_sg(). - - Most drivers don't have this problem; it is safe to say Y here. config IOMMU_HELPER def_bool PPC64 -- 1.6.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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