arm64: dma-mapping: Fix dma_mapping_error() when bypassing SWIOTLB

When bypassing SWIOTLB on small-memory systems, we need to avoid calling
into swiotlb_dma_mapping_error() in exactly the same way as we avoid
swiotlb_dma_supported(), because the former also relies on SWIOTLB state
being initialised.

Under the assumptions for which we skip SWIOTLB, dma_map_{single,page}()
will only ever return the DMA-offset-adjusted physical address of the
page passed in, thus we can report success unconditionally.

Fixes: b67a8b29 ("arm64: mm: only initialize swiotlb when necessary")
CC: stable@vger.kernel.org
CC: Jisheng Zhang <jszhang@marvell.com>
Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/mm/dma-mapping.c

@@ -356,6 +356,13 @@ static int __swiotlb_dma_supported(struct device *hwdev, u64 mask)
 	return 1;
 }
 
+static int __swiotlb_dma_mapping_error(struct device *hwdev, dma_addr_t addr)
+{
+	if (swiotlb)
+		return swiotlb_dma_mapping_error(hwdev, addr);
+	return 0;
+}
+
 static struct dma_map_ops swiotlb_dma_ops = {
 	.alloc = __dma_alloc,
 	.free = __dma_free,
@@ -370,7 +377,7 @@ static struct dma_map_ops swiotlb_dma_ops = {
 	.sync_sg_for_cpu = __swiotlb_sync_sg_for_cpu,
 	.sync_sg_for_device = __swiotlb_sync_sg_for_device,
 	.dma_supported = __swiotlb_dma_supported,
-	.mapping_error = swiotlb_dma_mapping_error,
+	.mapping_error = __swiotlb_dma_mapping_error,
 };
 
 static int __init atomic_pool_init(void)