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@xxxxxxxxxxx> 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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