diff mbox series

[V2,3/6] spi: bcm2835: added comment about different bus behaviour of DMA mode

Message ID 20190423201513.8073-4-kernel@martin.sperl.org (mailing list archive)
State New, archived
Headers show
Series spi: bcm2835: improvements | expand

Commit Message

Martin Sperl April 23, 2019, 8:15 p.m. UTC 
From: Martin Sperl <kernel@martin.sperl.org>

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

---
 drivers/spi/spi-bcm2835.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--
2.11.0
diff mbox series

Patch

diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index a64bfa8e0710..3140d952c03a 100644
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -828,7 +828,10 @@  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);