Patch "backlight: tdo24m: Fix the SPI CS between transfers" has been added to the 4.15-stable tree

This is a note to let you know that I've just added the patch titled

backlight: tdo24m: Fix the SPI CS between transfers

to the 4.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
backlight-tdo24m-fix-the-spi-cs-between-transfers.patch
and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Robert Jarzmik <[email protected]>
Date: Thu, 28 Dec 2017 09:27:41 +0100
Subject: backlight: tdo24m: Fix the SPI CS between transfers

From: Robert Jarzmik <[email protected]>

[ 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.

---
 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(-)

@@ -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,
 	};
 

@@ -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);
 

@@ -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,
 	};
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.15/backlight-tdo24m-fix-the-spi-cs-between-transfers.patch