From mboxrd@z Thu Jan 1 00:00:00 1970 From: kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org Subject: [PATCH V2 3/6] spi: bcm2835: added comment about different bus behaviour of DMA mode Date: Tue, 23 Apr 2019 20:15:10 +0000 Message-ID: <20190423201513.8073-4-kernel@martin.sperl.org> References: <20190423201513.8073-1-kernel@martin.sperl.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Mark Brown , Eric Anholt , Stefan Wahren , linux-spi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-rpi-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org Return-path: In-Reply-To: <20190423201513.8073-1-kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-rpi-kernel" Errors-To: linux-rpi-kernel-bounces+glkr-linux-rpi-kernel=m.gmane.org-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org List-Id: linux-spi.vger.kernel.org From: Martin Sperl 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 --- 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 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); -- 2.11.0