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

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

Signed-off-by: Frode Isaksen <fisaksen@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-davinci.c b/drivers/spi/spi-davinci.c
index ca122165a3c6f67e5a36b32d84a3be26bb1e1d80..75c658e4e48774ee4ab478c1a390f147ee891424 100644 (file)
--- 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)
 
        reinit_completion(&dspi->done);
 
-       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 */
                dspi->wcount--;
                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);