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Concurrent updates of flags that modify other bits are lost. Add gpiod_update_flags() - it replaces a masked set of bits with try_cmpxchg() loop. All bits are updated in one atomic step so no other thread can observe it half-done. Unmasked bits are not rewritten with stale values. Signed-off-by: Bartosz Golaszewski --- drivers/gpio/gpiolib.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/drivers/gpio/gpiolib.h b/drivers/gpio/gpiolib.h index 650a702741dfb938fbdf11db65a46ac85b6af512..10659ffcf2baef9d4a7584858cda1849b26c12e8 100644 --- a/drivers/gpio/gpiolib.h +++ b/drivers/gpio/gpiolib.h @@ -9,6 +9,7 @@ #ifndef GPIOLIB_H #define GPIOLIB_H +#include #include #include #include @@ -223,6 +224,26 @@ struct gpio_desc { #endif }; +/** + * gpiod_update_flags() - Atomically update several descriptor flags at once + * @desc: GPIO descriptor to update. + * @mask: Bits (not bit numbers) to modify. + * @val: New values for the bits selected by @mask. + * + * Replace the bits in @mask with the corresponding bits of @val in a single + * atomic step, so that no other context can observe a half-updated state of + * these bits. Bits outside of @mask are never rewritten with stale values, so + * concurrent atomic bit operations on them are preserved. + */ +static inline void gpiod_update_flags(struct gpio_desc *desc, + unsigned long mask, unsigned long val) +{ + unsigned long old = READ_ONCE(desc->flags); + + while (!try_cmpxchg(&desc->flags, &old, (old & ~mask) | (val & mask))) + ; +} + #define gpiod_not_found(desc) (IS_ERR(desc) && PTR_ERR(desc) == -ENOENT) struct gpio_chip_guard { -- 2.47.3