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| author | Martin Sperl | 2019-04-23 22:15:10 +0200 |
|---|---|---|
| committer | Mark Brown | 2019-05-08 10:58:54 +0200 |
| commit | c41d62b06cb92289ab5db9d37a0f27fe6271fa34 (patch) | |
| tree | a8fed8e77108b175647dc2c740746f5c4f0bf4da /drivers/spi | |
| parent | spi: bcm2835: Avoid 64-bit arithmetic in xfer len calc (diff) | |
| download | kernel-qcow2-linux-c41d62b06cb92289ab5db9d37a0f27fe6271fa34.tar.gz kernel-qcow2-linux-c41d62b06cb92289ab5db9d37a0f27fe6271fa34.tar.xz kernel-qcow2-linux-c41d62b06cb92289ab5db9d37a0f27fe6271fa34.zip | |
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>
Diffstat (limited to 'drivers/spi')
| -rw-r--r-- | drivers/spi/spi-bcm2835.c | 5 |
1 files changed, 4 insertions, 1 deletions
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); |