Re: [PATCHv7 9/9] ARM: dma-mapping: add support for IOMMU mapper

[Subash Patel <subashrp@xxxxxxxxx>]

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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