linux-kernel - [PATCH 2/2] ARM: sunxi: spi: add notice about SPI FIFO limit.

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Date:	Fri, 26 Feb 2016 07:56:57 +0200
From:	Priit Laes <plaes@...es.org>
To:	Mark Brown <broonie@...nel.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Chen-Yu Tsai <wens@...e.org>
Cc:	linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Emilio López <emilio@...pez.com.ar>,
	Michal Suchanek <hramrach@...il.com>
Subject: [PATCH 2/2] ARM: sunxi: spi: add notice about SPI FIFO limit.

From: Michal Suchanek <hramrach@...il.com>

When testing SPI without DMA I noticed that filling the FIFO on the
spi controller causes timeout. This should never happen with DMA support
so just adding a comment.

Signed-off-by: Michal Suchanek <hramrach@...il.com>
---
 drivers/spi/spi-sun4i.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index 78141a6..b750664 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -333,7 +333,9 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 		sun4i_spi_write(sspi, SUN4I_DMA_CTL_REG, 0);
 
 		/* Fill the TX FIFO */
-		sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
+		/* Filling the fifo fully causes timeout for some reason - at least on spi2 on a10s */
+		/* The can_dma check is txlen >= SUN4I_FIFO_DEPTH so with DMA this should never happen anyway. */
+		sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH - 1);
 	}
 
 	/* Start the transfer */
-- 
2.7.2