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    Subject[PATCH 4.9 143/310] backlight: tdo24m: Fix the SPI CS between transfers
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

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

    From: Robert Jarzmik <robert.jarzmik@free.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@gmail.com>
    Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
    Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
    Signed-off-by: Lee Jones <lee.jones@linaro.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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,
    };


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