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    Subject[PATCH AUTOSEL 6.0 12/44] spi: stm32: fix stm32_spi_prepare_mbr() that halves spi clk for every run
    Date
    From: Sean Nyekjaer <sean@geanix.com>

    [ Upstream commit 62aa1a344b0904549f6de7af958e8a1136fd5228 ]

    When this driver is used with a driver that uses preallocated spi_transfer
    structs. The speed_hz is halved by every run. This results in:

    spi_stm32 44004000.spi: SPI transfer setup failed
    ads7846 spi0.0: SPI transfer failed: -22

    Example when running with DIV_ROUND_UP():
    - First run; speed_hz = 1000000, spi->clk_rate 125000000
    div 125 -> mbrdiv = 7, cur_speed = 976562
    - Second run; speed_hz = 976562
    div 128,00007 (roundup to 129) -> mbrdiv = 8, cur_speed = 488281
    - Third run; speed_hz = 488281
    div 256,000131072067109 (roundup to 257) and then -EINVAL is returned.

    Use DIV_ROUND_CLOSEST to allow to round down and allow us to keep the
    set speed.

    Signed-off-by: Sean Nyekjaer <sean@geanix.com>
    Link: https://lore.kernel.org/r/20221103080043.3033414-1-sean@geanix.com
    Signed-off-by: Mark Brown <broonie@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/spi/spi-stm32.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
    index 6fe617b445a5..d6833361409d 100644
    --- a/drivers/spi/spi-stm32.c
    +++ b/drivers/spi/spi-stm32.c
    @@ -434,7 +434,7 @@ static int stm32_spi_prepare_mbr(struct stm32_spi *spi, u32 speed_hz,
    u32 div, mbrdiv;

    /* Ensure spi->clk_rate is even */
    - div = DIV_ROUND_UP(spi->clk_rate & ~0x1, speed_hz);
    + div = DIV_ROUND_CLOSEST(spi->clk_rate & ~0x1, speed_hz);

    /*
    * SPI framework set xfer->speed_hz to master->max_speed_hz if
    --
    2.35.1
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