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

From: [email-masked] (Robin Murphy)
Date: Fri, 29 May 2015 18:13:36 +0100

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:
>> 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 <[email-masked]>
>> ---
>>   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;

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.