[PATCH 1/5] spi: dw: fix first spi transfer with dma always fallback to PIO

[Jisheng Zhang <jszhang@kernel.org>]

Even with proper dma engine support, the first spi transfer always
fallback to PIO, the reason is the dws->n_bytes is 0 after
initialization, so the dw_spi_can_dma() calling from __spi_map_msg()
return false, thus both tx_sg_mapped and rx_sg_mapped are false, so
for the first spi transfer, the spi_xfer_is_dma_mapped() reports false
thus fallback to PIO.

Although this brings no harm, we can simply fix this issue by
calcuating the "n_bytes" from xfer->bits_per_word.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 drivers/spi/spi-dw-dma.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-dw-dma.c b/drivers/spi/spi-dw-dma.c
index fe726b9b1780..bd70a7ed8067 100644
--- a/drivers/spi/spi-dw-dma.c
+++ b/drivers/spi/spi-dw-dma.c
@@ -247,11 +247,12 @@ static bool dw_spi_can_dma(struct spi_controller *ctlr,
 {
 	struct dw_spi *dws = spi_controller_get_devdata(ctlr);
 	enum dma_slave_buswidth dma_bus_width;
+	u8 n_bytes = roundup_pow_of_two(BITS_TO_BYTES(xfer->bits_per_word));
 
 	if (xfer->len <= dws->fifo_len)
 		return false;
 
-	dma_bus_width = dw_spi_dma_convert_width(dws->n_bytes);
+	dma_bus_width = dw_spi_dma_convert_width(n_bytes);
 
 	return dws->dma_addr_widths & BIT(dma_bus_width);
 }
-- 
2.53.0