On Fri, Aug 02, 2013 at 12:59:00PM +0100, Stefano Stabellini wrote:

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

quoted

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.

I was more curious about the NEED_SG_DMA_LENGTH and IOMMU_HELPER.
I think the NEED_SG_DMA_LENGTH is optional? Or does SWIOTLB complain
about? I do recall seeing a patch for this at some point but it was
malformed. It was just changing SWIOTLB to use a macro for
sg->dma_length or such.

But the IOMMU_HELPER? That seems odds as the DMA API (which as you know
is what SWIOTLB hooks up to) is _below_ the IOMMU API.  Ah, it is 
'iommu_is_span_boundary' function.  Gotcha.

Could you mention that in the git commit please? Just say that SWIOTLB
uses some of the common code that IOMMU API uses - which is in the
lib/iommu_helper.c hence the need for that.

And for the NEED_SG_DMA_LENGTH let me dig up the patch at some point and
send it your way so you can make it part of this series.