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    Subject[PATCH 5.10 210/593] spi: Avoid undefined behaviour when counting unused native CSs
    Date
    From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

    [ Upstream commit f60d7270c8a3d2beb1c23ae0da42497afa3584c2 ]

    ffz(), that has been used to count unused native CSs,
    might cause undefined behaviour when called against ~0U.
    To fix that, open code it with ffs(~value) - 1.

    Fixes: 7d93aecdb58d ("spi: Add generic support for unused native cs with cs-gpios")
    Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    Link: https://lore.kernel.org/r/20210420164425.40287-2-andriy.shevchenko@linux.intel.com
    Signed-off-by: Mark Brown <broonie@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/spi/spi.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
    index a1a85f0baf7c..8c261eac2cee 100644
    --- a/drivers/spi/spi.c
    +++ b/drivers/spi/spi.c
    @@ -2614,7 +2614,7 @@ static int spi_get_gpio_descs(struct spi_controller *ctlr)
    native_cs_mask |= BIT(i);
    }

    - ctlr->unused_native_cs = ffz(native_cs_mask);
    + ctlr->unused_native_cs = ffs(~native_cs_mask) - 1;

    if ((ctlr->flags & SPI_MASTER_GPIO_SS) && num_cs_gpios &&
    ctlr->max_native_cs && ctlr->unused_native_cs >= ctlr->max_native_cs) {
    --
    2.30.2


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