Sorry for digging this very late. But as part of integrating dma_map v7 & sysmmu v12 on 3.3-rc5, I am facing below issue:
a) By un-selecting IOMMU in menu config, I am able to allocate memory in vb2-dma-contig
b) When I enable SYSMMU support for the IP's, I am receiving below fault:
Unhandled fault: external abort on non-linefetch (0x818) at 0xb6f55000
I think this has something to do with the access to the SYSMMU registers for writing the page table. Has anyone of you faced this issue while testing these(dma_map+iommu) patches on kernel mentioned above? This must be something related to recent changes, as I didn't have issues with these patches on 3.2 kernel.
Regards, Subash
On 03/02/2012 01:35 PM, KyongHo Cho wrote:
On Thu, Mar 1, 2012 at 12:04 AM, Marek Szyprowski m.szyprowski@samsung.com wrote:
+/**
- arm_iommu_map_sg - map a set of SG buffers for streaming mode DMA
- @dev: valid struct device pointer
- @sg: list of buffers
- @nents: number of buffers to map
- @dir: DMA transfer direction
- Map a set of buffers described by scatterlist in streaming mode for DMA.
- The scatter gather list elements are merged together (if possible) and
- tagged with the appropriate dma address and length. They are obtained via
- sg_dma_{address,length}.
- */
+int arm_iommu_map_sg(struct device *dev, struct scatterlist *sg, int nents,
enum dma_data_direction dir, struct dma_attrs *attrs)+{
struct scatterlist *s = sg, *dma = sg, *start = sg;int i, count = 0;unsigned int offset = s->offset;unsigned int size = s->offset + s->length;unsigned int max = dma_get_max_seg_size(dev);for (i = 1; i< nents; i++) {s->dma_address = ARM_DMA_ERROR;s->dma_length = 0;s = sg_next(s);if (s->offset || (size& ~PAGE_MASK) || size + s->length> max) {if (__map_sg_chunk(dev, start, size,&dma->dma_address,dir)< 0)goto bad_mapping;dma->dma_address += offset;dma->dma_length = size - offset;size = offset = s->offset;start = s;dma = sg_next(dma);count += 1;}size += s->length;}if (__map_sg_chunk(dev, start, size,&dma->dma_address, dir)< 0)goto bad_mapping;dma->dma_address += offset;dma->dma_length = size - offset;return count+1;+bad_mapping:
for_each_sg(sg, s, count, i)__iommu_remove_mapping(dev, sg_dma_address(s), sg_dma_len(s));return 0;+}
This looks that the given sg list specifies the list of physical memory chunks and the list of IO virtual memory chunks at the same time after calling arm_dma_map_sg(). It can happen that dma_address and dma_length of a sg entry does not correspond to physical memory information of the sg entry.
I think it is beneficial for handling IO virtual memory.
However, I worry about any other problems caused by a single sg entry contains information from 2 different context.
Regards,
Cho KyongHo.
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