[PATCH 2/4] iommu: Implement common IOMMU ops for DMA mapping

[yong.wu@mediatek.com (Yong Wu)]

Hi Robin,
    Thanks.

    While we test venc in v4l2, we get a problem:
    When we enter the funtion[0], it will be break unexpectedly in the
funcion[1] while the offset of sg table is not zero. It is ok if the
offset is zero. Then I add more log in dma-iommu.c, please help check
below.
    All we tested it based on dma v2. and have not tested it on v3 yet.
The code of iommu-map-sg seems the same. if it's fixed in v3, I'm very
sorry. The map_sg in mtk-iommu use default_iommu_map_sg.
    Any question please tell me, Thanks very much. 

[0]http://lxr.free-electrons.com/source/drivers/media/v4l2-core/videobuf2-dma-contig.c#L564	[1]http://lxr.free-electrons.com/source/drivers/media/v4l2-core/videobuf2-dma-contig.c#L70


On Wed, 2015-05-27 at 15:09 +0100, Robin Murphy wrote:
> Taking inspiration from the existing arch/arm code, break out some
> generic functions to interface the DMA-API to the IOMMU-API. This will
> do the bulk of the heavy lifting for IOMMU-backed dma-mapping.
> 
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/iommu/Kconfig     |   7 +
>  drivers/iommu/Makefile    |   1 +
>  drivers/iommu/dma-iommu.c | 560 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/dma-iommu.h |  94 ++++++++
>  4 files changed, 662 insertions(+)
>  create mode 100644 drivers/iommu/dma-iommu.c
>  create mode 100644 include/linux/dma-iommu.h
> 
[snip]
> +static int __finalise_sg(struct device *dev, struct scatterlist *sg, int nents,
> +		dma_addr_t dma_addr)
> +{
> +	struct scatterlist *s, *seg = sg;
> +	unsigned long seg_mask = dma_get_seg_boundary(dev);
> +	unsigned int max_len = dma_get_max_seg_size(dev);
> +	unsigned int seg_len = 0, seg_dma = 0;
> +	int i, count = 1;
> +
> +	for_each_sg(sg, s, nents, i) {
> +		/* Un-swizzling the fields here, hence the naming mismatch */
> +		unsigned int s_offset = sg_dma_address(s);
> +		unsigned int s_length = sg_dma_len(s);
> +		unsigned int s_dma_len = s->length;
> +
> +		s->offset = s_offset;
> +		s->length = s_length;
> +		sg_dma_address(s) = DMA_ERROR_CODE;
> +		sg_dma_len(s) = 0;
> +
> +		if (seg_len && (seg_dma + seg_len == dma_addr + s_offset) &&
> +		    (seg_len + s_dma_len <= max_len) &&
> +		    ((seg_dma & seg_mask) <= seg_mask - (seg_len + s_length))
> +		   ) {
> +			sg_dma_len(seg) += s_dma_len;
> +		} else {
> +			if (seg_len) {
> +				seg = sg_next(seg);
> +				count++;
> +			}
> +			sg_dma_len(seg) = s_dma_len;
> +			sg_dma_address(seg) = dma_addr + s_offset;
   Here the value of sg_dma_address have added s_offset, but
sg_dma_len(seg) still is s_dma_len.
   In the first loop, s_dma_len is from s->length which is alignd by
"s_length = iova_align(iovad, s_length + s_offset);" in
the interface iommu_dma_map_sg.
> +
> +			seg_len = s_offset;
> +			seg_dma = dma_addr + s_offset;
> +		}
> +		seg_len += s_length;
> +		dma_addr += s_dma_len;
> +	}
> +	return count;
> +}
> +
> +static void __invalidate_sg(struct scatterlist *sg, int nents)
> +{
> +	struct scatterlist *s;
> +	int i;
> +
> +	for_each_sg(sg, s, nents, i) {
> +		if (sg_dma_address(s) != DMA_ERROR_CODE)
> +			s->offset = sg_dma_address(s);
> +		if (sg_dma_len(s))
> +			s->length = sg_dma_len(s);
> +		sg_dma_address(s) = DMA_ERROR_CODE;
> +		sg_dma_len(s) = 0;
> +	}
> +}
> +
> +int iommu_dma_map_sg(struct device *dev, struct scatterlist *sg,
> +		int nents, int prot, bool coherent)
> +{
> +	struct iommu_dma_domain *dom = arch_get_dma_domain(dev);
> +	struct iova_domain *iovad = dom->iovad;
> +	struct iova *iova;
> +	struct scatterlist *s;
> +	dma_addr_t dma_addr;
> +	size_t iova_len = 0;
> +	int i;
> +
> +	/*
> +	 * Work out how much IOVA space we need, and align the segments to
> +	 * IOVA granules for the IOMMU driver to handle. With some clever
> +	 * trickery we can modify the list in a reversible manner.
> +	 */
> +	for_each_sg(sg, s, nents, i) {
> +		size_t s_offset = iova_offset(iovad, s->offset);
> +		size_t s_length = s->length;
> +
> +		sg_dma_address(s) = s->offset;
> +		sg_dma_len(s) = s_length;
> +		s->offset -= s_offset;
> +		s_length = iova_align(iovad, s_length + s_offset);
> +		s->length = s_length;
At the begging, s->length is the length of valid data. but it's aligned
here.
> +
> +		iova_len += s_length;
> +	}
> +
> +	iova = __alloc_iova(dev, iova_len, coherent);
> +	if (!iova)
> +		goto out_restore_sg;
> +
> +	/*
> +	 * We'll leave any physical concatenation to the IOMMU driver's
> +	 * implementation - it knows better than we do.
> +	 */
> +	dma_addr = iova_dma_addr(iovad, iova);
> +	if (iommu_map_sg(dom->domain, dma_addr, sg, nents, prot) < iova_len)
> +		goto out_free_iova;
> +
> +	return __finalise_sg(dev, sg, nents, dev_dma_addr(dev, dma_addr));
> +
> +out_free_iova:
> +	__free_iova(iovad, iova);
> +out_restore_sg:
> +	__invalidate_sg(sg, nents);
> +	return 0;
> +}
> +
[snip]