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

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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>
This commit is contained in:
Martin Sperl 2019-04-23 20:15:10 +00:00 committed by Mark Brown
parent 7f1922eb3a
commit c41d62b06c
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GPG Key ID: 24D68B725D5487D0
1 changed files with 4 additions and 1 deletions
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5
drivers/spi/spi-bcm2835.c
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@ -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);