Re: [Intel-gfx] [PATCH 0/8] Convert the intel iommu driver to the dma-iommu api

Tvrtko Ursulin
2020-09-08T15:37:56Z

Hi,

On 27/08/2020 22:36, Logan Gunthorpe wrote:
> On 2020-08-23 6:04 p.m., Tom Murphy wrote:
>> I have added a check for the sg_dma_len == 0 :
>> """
>> } __sgt_iter(struct scatterlist *sgl, bool dma) {
>> struct sgt_iter s = { .sgp = sgl };
>>
>> + if (sgl && sg_dma_len(sgl) == 0)
>> + s.sgp = NULL;
>>
>> if (s.sgp) {
>> .....
>> """
>> at location [1].
>> but it doens't fix the problem.
>
> Based on my read of the code, it looks like we also need to change usage
> of sgl->length... Something like the rough patch below, maybe?

This thread was brought to my attention and I initially missed this
reply. Essentially I came to the same conclusion about the need to use
sg_dma_len. One small correction below:

> Also, Tom, do you have an updated version of the patchset to convert the
> Intel IOMMU to dma-iommu available? The last one I've found doesn't
> apply cleanly (I'm assuming parts of it have been merged in slightly
> modified forms).
>
> Thanks,
>
> Logan
>
> --
>
> diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h
> b/drivers/gpu/drm/i915/i915
> index b7b59328cb76..9367ac801f0c 100644
> --- a/drivers/gpu/drm/i915/i915_scatterlist.h
> +++ b/drivers/gpu/drm/i915/i915_scatterlist.h
> @@ -27,13 +27,19 @@ static __always_inline struct sgt_iter {
> } __sgt_iter(struct scatterlist *sgl, bool dma) {
> struct sgt_iter s = { .sgp = sgl };
>
> + if (sgl && !sg_dma_len(s.sgp))

I'd extend the condition to be, just to be safe:

if (dma && sgl && !sg_dma_len(s.sgp))

> + s.sgp = NULL;
> +
> if (s.sgp) {
> s.max = s.curr = s.sgp->offset;
> - s.max += s.sgp->length;
> - if (dma)
> +
> + if (dma) {
> + s.max += sg_dma_len(s.sgp);
> s.dma = sg_dma_address(s.sgp);
> - else
> + } else {
> + s.max += s.sgp->length;
> s.pfn = page_to_pfn(sg_page(s.sgp));
> + }

Otherwise has this been tested or alternatively how to test it? (How to
repro the issue.)

Regards,

Tvrtko