On 18.10.2022 10:24, Christoph Hellwig wrote:
> @@ -127,19 +128,22 @@ static inline unsigned int i915_sg_dma_sizes(struct scatterlist *sg)
> return page_sizes;
> }
>
> -static inline unsigned int i915_sg_segment_size(void)
> +static inline unsigned int i915_sg_segment_size(struct device *dev)
> {
> - unsigned int size = swiotlb_max_segment();
> -
> - if (size == 0)
> - size = UINT_MAX;
> -
> - size = rounddown(size, PAGE_SIZE);
> - /* swiotlb_max_segment_size can return 1 byte when it means one page. */
> - if (size < PAGE_SIZE)
> - size = PAGE_SIZE;
> -
> - return size;
> + size_t max = min_t(size_t, UINT_MAX, dma_max_mapping_size(dev));
> +
> + /*
> + * Xen on x86 can reshuffle pages under us. The DMA API takes
> + * care of that both in dma_alloc_* (by calling into the hypervisor
> + * to make the pages contigous) and in dma_map_* (by bounce buffering).
> + * But i915 abuses ignores the coherency aspects of the DMA API and
> + * thus can't cope with bounce buffering actually happening, so add
> + * a hack here to force small allocations and mapping when running on
> + * Xen. (good luck with TDX, btw --hch)
> + */
> + if (IS_ENABLED(CONFIG_X86) && xen_domain())
> + max = PAGE_SIZE;
> + return round_down(max, PAGE_SIZE);
> }
Shouldn't this then be xen_pv_domain() that you use here, and - if you
really want IS_ENABLED() in addition - CONFIG_XEN_PV?
Jan
