On Fri, Dec 08, 2023 at 02:12:45PM +0100, Linus Walleij wrote: > On Thu, Dec 7, 2023 at 7:38 PM Bartosz Golaszewski <brgl@xxxxxxxx> wrote: > > > The reason for that is that I'm stuck on some corner-cases related to > > the GPIO <-> pinctrl interaction. Specifically the fact that we have > > GPIOLIB API functions that may be called from atomic context which may > > end up calling into pinctrl where a mutex will be acquired. > > OK I see the problem. > > > An example of that is any of the GPIO chips that don't set the > > can_sleep field in struct gpio_chip but still use > > gpiochip_generic_config() (e.g. tegra186). We can then encounter the > > following situation: > > > > irq_handler() // in atomic context > > gpiod_direction_output() // line is open-drain > > gpio_set_config() > > gpiochip_generic_config() > > pinctrl_gpio_set_config() > > mutex_lock() > > > > Currently we don't take any locks nor synchronize in any other way > > (which is wrong as concurrent gpiod_direction_output() and > > gpiod_direction_input() will get in each other's way). > > The only thing that really make sense to protect from here is > concurrent access to the same register (such as if a single > register contains multiple bits to set a number of GPIOs at > output or input). > > The real usecases for gpiod_direction_* I know of are limited to: > > 1. Once when the GPIO is obtained. > > 2. In strict sequence switching back and forth as in > drivers/i2c/busses/i2c-cbus-gpio.c > cbus_transfer() Isn't this a very special case already? cbus_transfer() holds the spin lock across the entire function, so it will only work for a very small set of GPIO providers anyway, right? Anything that's sleepable just is not going to work. I suspect that direction configuration is then also not going to sleep, so this should be fine. Thierry
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