linux-kernel - [PATCH v2] spi: spi-imx: fix off-by-one in mx51 CPU mode burst length

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Message-ID: <20240313210258.5990-1-adam@jessamine.co.uk>
Date: Wed, 13 Mar 2024 20:58:19 +0000
From: Adam Butcher <adam@...samine.co.uk>
To: broonie@...nel.org,
	benjamin@...ler.one,
	carlos.song@....com,
	s.hauer@...gutronix.de,
	shawnguo@...nel.org,
	stefanmoring@...il.com
Cc: kernel@...gutronix.de,
	linux-imx@....com,
	linux-kernel@...r.kernel.org,
	linux-spi@...r.kernel.org,
	adam@...samine.co.uk
Subject: [PATCH v2] spi: spi-imx: fix off-by-one in mx51 CPU mode burst length

From: Adam Butcher <adam@...samine.co.uk>

992e1211dc91 ("spi: imx: fix the burst length at DMA mode and CPU mode")
corrects three cases of setting the ECSPI burst length but erroneously
leaves the in-range CPU case one bit to big (in that field a value of
0 means 1 bit).  The effect was that transmissions that should have been
8-bit bytes appeared as 9-bit causing failed communication with SPI
devices.

Link: https://lore.kernel.org/all/20240201105451.507005-1-carlos.song@nxp.com/
Link: https://lore.kernel.org/all/20240204091912.36488-1-carlos.song@nxp.com/
Fixes: 992e1211dc91 ("spi: imx: fix the burst length at DMA mode and CPU mode")
Signed-off-by: Adam Butcher <adam@...samine.co.uk>
---

This is a cleaned up version of my earlier emails after the mess webmail
and I made of the previous re-address.  The patch itself is no different,
but I've moved the discussion part here and sent with git send-email so
hopefully no more issues.

The original patch submission up to v4 (first link above) did not contain
the bug that this patch fixes.  It was introduced in the v5 update (second
link).

---
 drivers/spi/spi-imx.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
index 7c1fcd5ed52f7..100552e6c56bc 100644
--- a/drivers/spi/spi-imx.c
+++ b/drivers/spi/spi-imx.c
@@ -743,8 +743,8 @@ static int mx51_ecspi_prepare_transfer(struct spi_imx_data *spi_imx,
 				ctrl |= (MX51_ECSPI_CTRL_MAX_BURST * BITS_PER_BYTE - 1)
 						<< MX51_ECSPI_CTRL_BL_OFFSET;
 			else
-				ctrl |= spi_imx->count / DIV_ROUND_UP(spi_imx->bits_per_word,
-						BITS_PER_BYTE) * spi_imx->bits_per_word
+				ctrl |= (spi_imx->count / DIV_ROUND_UP(spi_imx->bits_per_word,
+						BITS_PER_BYTE) * spi_imx->bits_per_word - 1)
 						<< MX51_ECSPI_CTRL_BL_OFFSET;
 		}
 	}
-- 
2.43.0