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charset="utf-8" Empirical testing shows that rcar-dmac engine can handle byte-aligned addresses without issues. Relax the driver by reducing RCAR_DMAC_MEMCPY_XFER_SIZE from 4 to 1 byte so that memcpy can run on unaligned buffers. One practical user is ntb_netdev + ntb_transport. On its TX path, skb->data often ends up 2 bytes off a 4-byte boundary due to the 16-byte headroom alignment (HH_DATA_MOD) combined with a 14-byte Ethernet header push, yielding a 4n+2 start address, falling back to CPU memcpy. With this change, rcar-dmac can be used there as well. In local testing, hacking skb->data to be 4-byte aligned while keeping RCAR_DMAC_MEMCPY_XFER_SIZE =3D 4 did not produce a measurable throughput difference compared to the unaligned case with this change, suggesting the previous 4-byte constraint was not performance-driven on the tested systems. Signed-off-by: Koichiro Den --- drivers/dma/sh/rcar-dmac.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c index 0c45ce8c74aa..c4d6c2f9a26b 100644 --- a/drivers/dma/sh/rcar-dmac.c +++ b/drivers/dma/sh/rcar-dmac.c @@ -303,7 +303,7 @@ struct rcar_dmac_of_data { #define RCAR_GEN4_DMACHCLR 0x0100 =20 /* Hardcode the MEMCPY transfer size to 4 bytes. */ -#define RCAR_DMAC_MEMCPY_XFER_SIZE 4 +#define RCAR_DMAC_MEMCPY_XFER_SIZE 1 =20 /* -----------------------------------------------------------------------= ------ * Device access --=20 2.48.1