Applied "spi: davinci: do not use DMA if transfer length is less than 16" to the spi tree

Mark Brown broonie at
Wed Mar 15 12:37:16 PDT 2017

The patch

   spi: davinci: do not use DMA if transfer length is less than 16

has been applied to the spi tree at


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tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
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>From 0718b764880434ac7a5b7c0f5cb2c805c589a807 Mon Sep 17 00:00:00 2001
From: Frode Isaksen <fisaksen at>
Date: Thu, 23 Feb 2017 19:01:59 +0100
Subject: [PATCH] spi: davinci: do not use DMA if transfer length is less than

Higher bitrate and lower CPU load if using PIO in this case.

Signed-off-by: Frode Isaksen <fisaksen at>
Signed-off-by: Mark Brown <broonie at>
 drivers/spi/spi-davinci.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/spi/spi-davinci.c b/drivers/spi/spi-davinci.c
index ca122165a3c6..75c658e4e487 100644
--- a/drivers/spi/spi-davinci.c
+++ b/drivers/spi/spi-davinci.c
@@ -109,6 +109,8 @@
 #define SPIDEF		0x4c
 #define SPIFMT0		0x50
+#define DMA_MIN_BYTES	16
 /* SPI Controller driver's private data. */
 struct davinci_spi {
 	struct spi_bitbang	bitbang;
@@ -479,7 +481,8 @@ static bool davinci_spi_can_dma(struct spi_master *master,
 	bool can_dma = false;
 	if (spicfg)
-		can_dma = spicfg->io_type == SPI_IO_TYPE_DMA;
+		can_dma = (spicfg->io_type == SPI_IO_TYPE_DMA) &&
+			(xfer->len >= DMA_MIN_BYTES);
 	return can_dma;
@@ -620,10 +623,9 @@ static int davinci_spi_bufs(struct spi_device *spi, struct spi_transfer *t)
-	if (spicfg->io_type == SPI_IO_TYPE_INTR)
-		set_io_bits(dspi->base + SPIINT, SPIINT_MASKINT);
-	if (spicfg->io_type != SPI_IO_TYPE_DMA) {
+	if (!davinci_spi_can_dma(spi->master, spi, t)) {
+		if (spicfg->io_type != SPI_IO_TYPE_POLL)
+			set_io_bits(dspi->base + SPIINT, SPIINT_MASKINT);
 		/* start the transfer */
 		tx_data = dspi->get_tx(dspi);
@@ -698,7 +700,7 @@ static int davinci_spi_bufs(struct spi_device *spi, struct spi_transfer *t)
 	clear_io_bits(dspi->base + SPIINT, SPIINT_MASKALL);
-	if (spicfg->io_type == SPI_IO_TYPE_DMA)
+	if (davinci_spi_can_dma(spi->master, spi, t))
 		clear_io_bits(dspi->base + SPIINT, SPIINT_DMA_REQ_EN);
 	clear_io_bits(dspi->base + SPIGCR1, SPIGCR1_SPIENA_MASK);

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