spi: rockchip: Config spi rx dma burst size depend on xfer length

The burst length can be adjusted according to the transmission
length to improve the transmission rate

Signed-off-by: Jon Lin <jon.lin@rock-chips.com>
Tested-by: Emil Renner Berthing <kernel@esmil.dk>
Reviewed-by: Emil Renner Berthing <kernel@esmil.dk>
Link: https://lore.kernel.org/r/20200723004356.6390-1-jon.lin@rock-chips.com
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-rockchip.c

@@ -384,6 +384,19 @@ static void rockchip_spi_dma_txcb(void *data)
 	spi_finalize_current_transfer(ctlr);
 }
 
+static u32 rockchip_spi_calc_burst_size(u32 data_len)
+{
+	u32 i;
+
+	/* burst size: 1, 2, 4, 8 */
+	for (i = 1; i < 8; i <<= 1) {
+		if (data_len & i)
+			break;
+	}
+
+	return i;
+}
+
 static int rockchip_spi_prepare_dma(struct rockchip_spi *rs,
 		struct spi_controller *ctlr, struct spi_transfer *xfer)
 {
@@ -397,7 +410,8 @@ static int rockchip_spi_prepare_dma(struct rockchip_spi *rs,
 			.direction = DMA_DEV_TO_MEM,
 			.src_addr = rs->dma_addr_rx,
 			.src_addr_width = rs->n_bytes,
-			.src_maxburst = 1,
+			.src_maxburst = rockchip_spi_calc_burst_size(xfer->len /
+								     rs->n_bytes),
 		};
 
 		dmaengine_slave_config(ctlr->dma_rx, &rxconf);
@@ -525,7 +539,8 @@ static void rockchip_spi_config(struct rockchip_spi *rs,
 		writel_relaxed(rs->fifo_len / 2 - 1, rs->regs + ROCKCHIP_SPI_RXFTLR);
 
 	writel_relaxed(rs->fifo_len / 2, rs->regs + ROCKCHIP_SPI_DMATDLR);
-	writel_relaxed(0, rs->regs + ROCKCHIP_SPI_DMARDLR);
+	writel_relaxed(rockchip_spi_calc_burst_size(xfer->len / rs->n_bytes) - 1,
+		       rs->regs + ROCKCHIP_SPI_DMARDLR);
 	writel_relaxed(dmacr, rs->regs + ROCKCHIP_SPI_DMACR);
 
 	/* the hardware only supports an even clock divisor, so