On 29/05/15 06:26, Yong Wu wrote:

Hi Robin,
     Thanks.

     While we test venc in v4l2, we get a problem:

Thanks as always for testing!

     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.

Bah, non-zero offset was about the only scatterlist case I wasn't able 
to get out of the EHCI driver...

     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:

quoted

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]

quoted

+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;

Does changing this to
			sg_dma_len(seg) = s_dma_len - s_offset;

make things behave as expected? Since the new unmap code no longer 
relies on adding up the individual segments to equal the IOVA size I 
don't _think_ that'll break anything here.

Robin.