linux-kernel - [PATCH 1/2] spi: sun6i: reduce DMA RX transfer width to single byte

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Message-ID: <20230827152558.5368-2-t.schramm@manjaro.org>
Date:   Sun, 27 Aug 2023 17:25:57 +0200
From:   Tobias Schramm <t.schramm@...jaro.org>
To:     Mark Brown <broonie@...nel.org>, Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>
Cc:     linux-spi@...r.kernel.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Tobias Schramm <t.schramm@...jaro.org>
Subject: [PATCH 1/2] spi: sun6i: reduce DMA RX transfer width to single byte

Through empirical testing it has been determined that sometimes RX SPI
transfers with DMA enabled return corrupted data. This is down to single
or even multiple bytes lost during DMA transfer from SPI peripheral to
memory. It seems the RX FIFO within the SPI peripheral can become
confused when performing bus read accesses wider than a single byte to it
during an active SPI transfer.

This patch reduces the width of individual DMA read accesses to the
RX FIFO to a single byte to mitigate that issue.

Signed-off-by: Tobias Schramm <t.schramm@...jaro.org>
---
 drivers/spi/spi-sun6i.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-sun6i.c b/drivers/spi/spi-sun6i.c
index 30d541612253..8fcb2696ec09 100644
--- a/drivers/spi/spi-sun6i.c
+++ b/drivers/spi/spi-sun6i.c
@@ -207,7 +207,7 @@ static int sun6i_spi_prepare_dma(struct sun6i_spi *sspi,
 		struct dma_slave_config rxconf = {
 			.direction = DMA_DEV_TO_MEM,
 			.src_addr = sspi->dma_addr_rx,
-			.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES,
+			.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE,
 			.src_maxburst = 8,
 		};
 
-- 
2.42.0