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Commit 191aee58 authored by FUJITA Tomonori's avatar FUJITA Tomonori Committed by Benjamin Herrenschmidt
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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It's out of date.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. 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. Users can still disable the virtual merging by the
boot parameter.

Signed-off-by: default avatarFUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
parent a9327296

arch/powerpc/Kconfig

+0 −13
Original line number Diff line number Diff line
@@ -313,19 +313,6 @@ config 8XX_MINIMAL_FPEMU 


	  It is recommended that you build a soft-float userspace instead.



config IOMMU_VMERGE

	bool "Enable IOMMU virtual merging"

	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

arch/powerpc/kernel/iommu.c

+1 −6
Original line number Diff line number Diff line
@@ -42,12 +42,7 @@ 


#define DBG(...)



#ifdef CONFIG_IOMMU_VMERGE

static int novmerge = 0;

#else

static int novmerge = 1;

#endif



static int novmerge;

static int protect4gb = 1;



static void __iommu_free(struct iommu_table *, dma_addr_t, unsigned int);