RE: [Linaro-mm-sig] [RFC 2/2] ARM: initial proof-of-concept IOMMU mapper for DMA-mapping

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hello,

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

> > 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>
> > ---
> ...
> > diff --git a/arch/arm/include/asm/dma-iommu.h b/arch/arm/include/asm/dma-
> iommu.h
> > new file mode 100644
> > index 0000000..c246ff3
> > --- /dev/null
> > +++ b/arch/arm/include/asm/dma-iommu.h
> ...
> > +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.

> > 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
> ...
> > +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




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