Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP

Christoph Hellwig
2022-03-24T05:57:51Z

On Wed, Mar 23, 2022 at 08:54:08PM +0000, Robin Murphy wrote:
> I'll admit I still never quite grasped the reason for also adding the
> override to swiotlb_sync_single_for_device() in aa6f8dcbab47, but I think
> by that point we were increasingly tired and confused and starting to
> second-guess ourselves (well, I was, at least). I don't think it's wrong
> per se, but as I said I do think it can bite anyone who's been doing
> dma_sync_*() wrong but getting away with it until now. If ddbd89deb7d3
> alone turns out to work OK then I'd be inclined to try a partial revert of
> just that one hunk.

Agreed. Let's try that first.

Oleksandr, can you try the patch below:

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 6db1c475ec827..6c350555e5a1c 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -701,13 +701,10 @@ void swiotlb_tbl_unmap_single(struct device *dev, phys_addr_t tlb_addr,
void swiotlb_sync_single_for_device(struct device *dev, phys_addr_t tlb_addr,
size_t size, enum dma_data_direction dir)
{
- /*
- * Unconditional bounce is necessary to avoid corruption on
- * sync_*_for_cpu or dma_ummap_* when the device didn't overwrite
- * the whole lengt of the bounce buffer.
- */
- swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE);
- BUG_ON(!valid_dma_direction(dir));
+ if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
+ swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE);
+ else
+ BUG_ON(dir != DMA_FROM_DEVICE);
}

void swiotlb_sync_single_for_cpu(struct device *dev, phys_addr_t tlb_addr,