2 Mar
2012
2 Mar
'12
8:05 a.m.
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.