linux-kernel - Re: [PATCH v2 1/3] backlight: tdo24m: fix the spi cs between transfers

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Message-ID: <20171215114025.4nmuz44xdecpzqt3@oak.lan>
Date:   Fri, 15 Dec 2017 11:40:25 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:     Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] backlight: tdo24m: fix the spi cs between
 transfers

On Fri, Oct 13, 2017 at 09:42:47PM +0200, Robert Jarzmik wrote:
> 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>

Didn't I already ack this one?


Daniel.

> ---
> Since v1: added 2 other panels
> ---
>  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(-)
> 
> diff --git a/drivers/video/backlight/corgi_lcd.c b/drivers/video/backlight/corgi_lcd.c
> index d7c239ea3d09..f5574060f9c8 100644
> --- 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 corgi_lcd *lcd, int adrs, uint8_t data)
>  	struct spi_message msg;
>  	struct spi_transfer xfer = {
>  		.len		= 1,
> -		.cs_change	= 1,
> +		.cs_change	= 0,
>  		.tx_buf		= lcd->buf,
>  	};
>  
> diff --git a/drivers/video/backlight/tdo24m.c b/drivers/video/backlight/tdo24m.c
> index eab1f842f9c0..e4bd63e9db6b 100644
> --- a/drivers/video/backlight/tdo24m.c
> +++ b/drivers/video/backlight/tdo24m.c
> @@ -369,7 +369,7 @@ static int tdo24m_probe(struct spi_device *spi)
>  
>  	spi_message_init(m);
>  
> -	x->cs_change = 1;
> +	x->cs_change = 0;
>  	x->tx_buf = &lcd->buf[0];
>  	spi_message_add_tail(x, m);
>  
> diff --git a/drivers/video/backlight/tosa_lcd.c b/drivers/video/backlight/tosa_lcd.c
> index 6a41ea92737a..4dc5ee8debeb 100644
> --- 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_device *spi, int adrs, uint8_t data)
>  	struct spi_message msg;
>  	struct spi_transfer xfer = {
>  		.len		= 1,
> -		.cs_change	= 1,
> +		.cs_change	= 0,
>  		.tx_buf		= buf,
>  	};
>  
> -- 
> 2.11.0
>