linux-kernel - [PATCH 4.14 041/138] backlight: tdo24m: Fix the SPI CS between transfers

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Date:   Wed, 11 Apr 2018 00:23:51 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andrea Adami <andrea.adami@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Lee Jones <lee.jones@...aro.org>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.14 041/138] backlight: tdo24m: Fix the SPI CS between transfers

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Robert Jarzmik <robert.jarzmik@...e.fr>

[ Upstream commit 2023b0524a6310e9ea80daf085f51c71bff9289f ]

Currently the LCD display (TD035S) on the cm-x300 platform is broken and
remains blank.

The TD0245S specification requires that the chipselect is toggled
between commands sent to the panel. This was also the purpose of the
former patch of commit f64dcac0b124 ("backlight: tdo24m: ensure chip
select changes between transfers").

Unfortunately, the "cs_change" field of a SPI transfer is
misleading. Its true meaning is that for a SPI message holding multiple
transfers, the chip select is toggled between each transfer, but for the
last transfer it remains asserted.

In this driver, all the SPI messages contain exactly one transfer, which
means that each transfer is the last of its message, and as a
consequence the chip select is never toggled.

Actually, there was a second bug hidding the first one, hence the
problem was not seen until v4.6. This problem was fixed by commit
a52db659c79c ("spi: pxa2xx: Fix cs_change management") for PXA based
boards.

This fix makes the TD035S work again on a cm-x300 board. The same
applies to other PXA boards, ie. corgi and tosa.

Fixes: a52db659c79c ("spi: pxa2xx: Fix cs_change management")
Reported-by: Andrea Adami <andrea.adami@...il.com>
Signed-off-by: Robert Jarzmik <robert.jarzmik@...e.fr>
Acked-by: Daniel Thompson <daniel.thompson@...aro.org>
Signed-off-by: Lee Jones <lee.jones@...aro.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/video/backlight/corgi_lcd.c |    2 +-
 drivers/video/backlight/tdo24m.c    |    2 +-
 drivers/video/backlight/tosa_lcd.c  |    2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/video/backlight/corgi_lcd.c
+++ b/drivers/video/backlight/corgi_lcd.c
@@ -177,7 +177,7 @@ static int corgi_ssp_lcdtg_send(struct c
 	struct spi_message msg;
 	struct spi_transfer xfer = {
 		.len		= 1,
-		.cs_change	= 1,
+		.cs_change	= 0,
 		.tx_buf		= lcd->buf,
 	};

--- a/drivers/video/backlight/tdo24m.c
+++ b/drivers/video/backlight/tdo24m.c
@@ -369,7 +369,7 @@ static int tdo24m_probe(struct spi_devic

 	spi_message_init(m);

-	x->cs_change = 1;
+	x->cs_change = 0;
 	x->tx_buf = &lcd->buf[0];
 	spi_message_add_tail(x, m);

--- a/drivers/video/backlight/tosa_lcd.c
+++ b/drivers/video/backlight/tosa_lcd.c
@@ -49,7 +49,7 @@ static int tosa_tg_send(struct spi_devic
 	struct spi_message msg;
 	struct spi_transfer xfer = {
 		.len		= 1,
-		.cs_change	= 1,
+		.cs_change	= 0,
 		.tx_buf		= buf,
 	};