spi: bcm2835: added comment about different bus behaviour of DMA mode

The DMA mode behaves slightly different than polling or interrupt driven
mode, so just document the fact

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Changelog:
  V1 -> V2: applied feedback by Stefan Wahren
            new in V2
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index b7bb07c9507dc4755d425c1dbd484f756c847175..0d8c97502f1477966fb634ee8cfa42c449c73bd9 100644 (file)
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -800,7 +800,10 @@ static int bcm2835_spi_transfer_one(struct spi_master *master,
        if (tfr->len < spi_used_hz / HZ_PER_BYTE)
                return bcm2835_spi_transfer_one_poll(master, spi, tfr, cs);
 
-       /* run in dma mode if conditions are right */
+       /* run in dma mode if conditions are right
+        * Note that unlike poll or interrupt mode DMA mode does not have
+        * this 1 idle clock cycle pattern but runs the spi clock without gaps
+        */
        if (master->can_dma && bcm2835_spi_can_dma(master, spi, tfr))
                return bcm2835_spi_transfer_one_dma(master, spi, tfr, cs);