amdgpu/TTM oopses since merging swiotlb_dma_ops into the dma_direct code

[Christoph Hellwig]

Hmm, I wonder if we are not actually using swiotlb in the end,
can you check if your dmesg contains this line or not?

PCI-DMA: Using software bounce buffering for IO (SWIOTLB)

If not I guess we found a bug in swiotlb exit vs is_swiotlb_buffer,
and you can try this patch:

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index d6361776dc5c..1fb6fd68b9c7 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -378,6 +378,8 @@ void __init swiotlb_exit(void)
 		memblock_free_late(io_tlb_start,
 				   PAGE_ALIGN(io_tlb_nslabs << IO_TLB_SHIFT));
 	}
+	io_tlb_start = 0;
+	io_tlb_end = 0;
 	io_tlb_nslabs = 0;
 	max_segment = 0;
 }