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spi: davinci: add comment about dummy tx buffer usage 

Add explanation about using the the rx buffer as the
dummy tx buffer.

Signed-off-by: Frode Isaksen <fisaksen@baylibre.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Frode Isaksen 2017-03-17 16:41:10 +01:00 committed by Mark Brown
parent 4dd9becbce
commit 1234e8398f
1 changed files with 5 additions and 1 deletions
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6
drivers/spi/spi-davinci.c
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@ -660,7 +660,11 @@ static int davinci_spi_bufs(struct spi_device *spi, struct spi_transfer *t)
goto err_desc;
if (!t->tx_buf) {
/* use rx buffer as dummy tx buffer */
/* To avoid errors when doing rx-only transfers with
* many SG entries (> 20), use the rx buffer as the
* dummy tx buffer so that dma reloads are done at the
* same time for rx and tx.
*/
t->tx_sg.sgl = t->rx_sg.sgl;
t->tx_sg.nents = t->rx_sg.nents;
}