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spi: Avoid undefined behaviour when counting unused native CSs

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[ Upstream commit f60d7270c8 ]

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: 7d93aecdb5 ("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>
This commit is contained in:
Andy Shevchenko 2021-04-20 19:44:25 +03:00 committed by Greg Kroah-Hartman
parent db5a7e22c9
commit 08d0aa16a1
1 changed files with 1 additions and 1 deletions
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2
drivers/spi/spi.c
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@ -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) {