On Wed, 31 Jul 2013, Konrad Rzeszutek Wilk wrote:

Stefano Stabellini [off-list ref] wrote:

quoted

Signed-off-by: Stefano Stabellini <redacted>
CC: will.deacon at arm.com
CC: linux at arm.linux.org.uk
---
arch/arm/Kconfig                   |    7 +++++++
arch/arm/include/asm/dma-mapping.h |   24 ++++++++++++++++++++++++
2 files changed, 31 insertions(+), 0 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index ba412e0..05125ab 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig

@@ -1832,6 +1832,13 @@ config CC_STACKPROTECTOR

	  neutralized via a kernel panic.
	  This feature requires gcc version 4.2 or above.

+config SWIOTLB
+	def_bool y
+	select NEED_SG_DMA_LENGTH
+
+config IOMMU_HELPER
+	def_bool SWIOTLB
+

Could you explain the purpose of these two a bit more please? 

SWIOTLB is not available on arm at the moment.
We need to make it available, otherwise SWIOTLB_XEN won't be able to
select it.

Similarly, IOMMU_HELPER is another lib Kconfig symbol needed by SWIOTLB
to compile.