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Commit 1234e839 authored by Frode Isaksen's avatar Frode Isaksen Committed by Mark Brown
Browse files

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: default avatarFrode Isaksen <fisaksen@baylibre.com>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 4dd9becb

drivers/spi/spi-davinci.c

+5 −1
Original line number Original line Diff line number Diff line
@@ -660,7 +660,11 @@ static int davinci_spi_bufs(struct spi_device *spi, struct spi_transfer *t) 
			goto err_desc;

			goto err_desc;





		if (!t->tx_buf) {

		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.sgl = t->rx_sg.sgl;

			t->tx_sg.nents = t->rx_sg.nents;

			t->tx_sg.nents = t->rx_sg.nents;

		}

		}