From c41d62b06cb92289ab5db9d37a0f27fe6271fa34 Mon Sep 17 00:00:00 2001 From: Martin Sperl Date: Tue, 23 Apr 2019 20:15:10 +0000 Subject: [PATCH] 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 Changelog: V1 -> V2: applied feedback by Stefan Wahren new in V2 Signed-off-by: Mark Brown --- drivers/spi/spi-bcm2835.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c index b7bb07c9507d..0d8c97502f14 100644 --- 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); -- 2.39.5