Hello,

On Thursday, July 14, 2011 8:33 PM Ramirez Luna, Omar wrote:

quoted

Add initial proof of concept implementation of DMA-mapping API for
devices that have IOMMU support. Right now only dma_alloc_coherent,
dma_free_coherent and dma_mmap_coherent functions are supported.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
---

...

quoted

diff --git a/arch/arm/include/asm/dma-iommu.h b/arch/arm/include/asm/dma-

iommu.h

quoted

new file mode 100644
index 0000000..c246ff3

--- /dev/null
+++ b/arch/arm/include/asm/dma-iommu.h

...

quoted

+int __init arm_iommu_assign_device(struct device *dev, dma_addr_t base,

dma_addr_t size);

__init causes a panic if the iommu is assigned after boot.

In OMAP3 the iommu driver controls isp and dsp address spaces, it is
loaded until any of those 2 drivers is needed.

Well, ok. This was just a proof-of-concept/rfc patch, so it was designed only
for our particular case.

quoted

diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index f8c6972..b6397c1 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c

...

quoted

+static void *arm_iommu_alloc_attrs(struct device *dev, size_t size,
+ ? ? ? ? ? dma_addr_t *handle, gfp_t gfp, struct dma_attrs *attrs)
+{
+ ? ? ? struct dma_iommu_mapping *mapping = dev->archdata.mapping;
+ ? ? ? struct page **pages;
+ ? ? ? void *addr = NULL;
+ ? ? ? pgprot_t prot;
+
+ ? ? ? if (dma_get_attr(DMA_ATTR_WRITE_COMBINE, attrs))
+ ? ? ? ? ? ? ? prot = pgprot_writecombine(pgprot_kernel);
+ ? ? ? else
+ ? ? ? ? ? ? ? prot = pgprot_dmacoherent(pgprot_kernel);
+
+ ? ? ? arm_iommu_init(dev);

I found useful to call arm_iommu_init inside arm_iommu_assign_device
instead. So, then gen_pool is created only once without the
mapping->pool check, instead of relying on the call to ...alloc_attrs,
which in my case I never use because I'm implementing
iommu_map|unmap_sg functions to see how it goes with the dma mapping.

Right, this is still on my todo list, but I wanted to focus on cleanup 
of dma mapping framework and cma first.

Best regards
-- 
Marek Szyprowski
Samsung Poland R&D Center