Re: [PATCH v8 12/23] dma: swiotlb: pass mapping attributes by reference

On Wed, Jul 29, 2026 at 02:35:36PM +0530, Aneesh Kumar K.V wrote:

Mostafa Saleh [off-list ref] writes:

quoted

On Fri, Jul 17, 2026 at 11:34:30PM +0530, Aneesh Kumar K.V (Arm) wrote:

quoted

Change swiotlb_tbl_map_single() to take the DMA mapping attributes by
reference and update the direct callers accordingly.

This is a preparatory change for a follow-up patch which updates the
attributes based on the selected swiotlb pool. Keeping the signature change
separate makes the follow-up patch easier to review.

I do not understand the point of this, why would
swiotlb_tbl_map_single() force attrs over the caller which should
already know the context (whether DMA is shared or not) which case
would this be useful to force from the SWIOTLB code?

The mapping request was for private memory, but the device could not use
it because the dma_capable() (force_dma_unencrypted() == true) check
failed. As a result, dma_direct_map_phys() allocated a swiotlb bounce
buffer, which is shared. Since the DMA now targets the shared bounce
buffer rather than the original private memory, the attributes must be
updated to reflect the new shared mapping.

dma_addr = phys_to_dma(dev, phys);
if (unlikely(!dma_capable(dev, dma_addr, size, true)))
	if (is_swiotlb_active(dev))
		return swiotlb_map(dev, phys, size, dir, attrs);

But it does not make sense to me to have it in such a low level
function, and it shouldn't change the attrs that was passed.

dma_direct_map_phys() is the right place to do this it should set
the correct attrs before calling swiotlb_map().

Thanks,
Mostafa

-aneesh