linux-kernel - Re: [PATCH v3] backlight: tdo24m: fix the spi cs between transfers

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Date:   Tue, 2 Jan 2018 15:38:41 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Robert Jarzmik <robert.jarzmik@...e.fr>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] backlight: tdo24m: fix the spi cs between transfers

On Thu, 28 Dec 2017, 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")

Since this fixes an old kernel, I'm not going to apply it for -fixes.

> 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>
> ---
> Since v1: added 2 other panels
> Since v2: added Daniel's ack
> ---
>  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(-)

Applied to -next, thanks.

-- 
Lee Jones
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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