Re: [PATCH v5 6/6] swiotlb: Remove pointless stride adjustment for allocations >= PAGE_SIZE

Christoph Hellwig
2024-02-29T15:48:01Z

On Thu, Feb 29, 2024 at 03:44:11PM +0000, Michael Kelley wrote:
> Any thoughts on how that historical behavior should apply if
> the DMA min_align_mask is non-zero, or the alloc_align_mask
> parameter to swiotbl_tbl_map_single() is non-zero? As currently
> used, alloc_align_mask is page aligned if the IOMMU granule is
> >= PAGE_SIZE. But a non-zero min_align_mask could mandate
> returning a buffer that is not page aligned. Perhaps do the
> historical behavior only if alloc_align_mask and min_align_mask
> are both zero?

I think the driver setting min_align_mask is a clear indicator
that the driver requested a specific alignment and the defaults
don't apply. For swiotbl_tbl_map_single as used by dma-iommu
I'd have to tak a closer look at how it is used.