From 1234e8398fe03267bf2e353e36825dbd0abc2fc6 Mon Sep 17 00:00:00 2001 From: Frode Isaksen Date: Fri, 17 Mar 2017 16:41:10 +0100 Subject: [PATCH] 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 Signed-off-by: Mark Brown --- drivers/spi/spi-davinci.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/spi/spi-davinci.c b/drivers/spi/spi-davinci.c index f37bbdd18d61..595acdcfc7d0 100644 --- a/drivers/spi/spi-davinci.c +++ b/drivers/spi/spi-davinci.c @@ -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; }