RE: [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper

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

Hello,

On Wednesday, March 07, 2012 12:22 AM Russell King - ARM Linux wrote:

> On Wed, Feb 29, 2012 at 04:04:22PM +0100, Marek Szyprowski wrote:
> > +static int arm_iommu_mmap_attrs(struct device *dev, struct vm_area_struct *vma,
> > +		    void *cpu_addr, dma_addr_t dma_addr, size_t size,
> > +		    struct dma_attrs *attrs)
> > +{
> > +	struct arm_vmregion *c;
> > +
> > +	vma->vm_page_prot = __get_dma_pgprot(attrs, vma->vm_page_prot);
> > +	c = arm_vmregion_find(&consistent_head, (unsigned long)cpu_addr);
> 
> What protects this against other insertions/removals from the list?

arm_vmregion_* functions have their own spinlock.

(snipped)

> > +	if (c) {
> > +		struct page **pages = c->priv;
> > +		__dma_free_remap(cpu_addr, size);
> > +		__iommu_remove_mapping(dev, handle, size);
> > +		__iommu_free_buffer(dev, pages, size);
> > +	}
> > +}
> > +
> > +/*
> > + * Map a part of the scatter-gather list into contiguous io address space
> > + */
> > +static int __map_sg_chunk(struct device *dev, struct scatterlist *sg,
> > +			  size_t size, dma_addr_t *handle,
> > +			  enum dma_data_direction dir)
> > +{
> > +	struct dma_iommu_mapping *mapping = dev->archdata.mapping;
> > +	dma_addr_t iova, iova_base;
> > +	int ret = 0;
> > +	unsigned int count;
> > +	struct scatterlist *s;
> > +
> > +	size = PAGE_ALIGN(size);
> > +	*handle = ARM_DMA_ERROR;
> > +
> > +	iova_base = iova = __alloc_iova(mapping, size);
> > +	if (iova == ARM_DMA_ERROR)
> > +		return -ENOMEM;
> > +
> > +	for (count = 0, s = sg; count < (size >> PAGE_SHIFT); s = sg_next(s))
> > +	{
> > +		phys_addr_t phys = page_to_phys(sg_page(s));
> > +		unsigned int len = PAGE_ALIGN(s->offset + s->length);
> > +
> > +		if (!arch_is_coherent())
> > +			__dma_page_cpu_to_dev(sg_page(s), s->offset, s->length, dir);
> > +
> > +		ret = iommu_map(mapping->domain, iova, phys, len, 0);
> 
> Dealing with phys addresses on one part and pages + offset + length
> in a different part doesn't look like a good idea.  Why can't there
> be some consistency?

Well, I have no idea how to be more consistent here. scatter-lists operates on 
pages + offsets + length parameters. iommu api operates on the whole pages, but
they are referred with physical address. Right now I cannot change any of it, 
at least not it the near future.

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