In the Linux kernel, the following vulnerability has been resolved:
pinctrl: mediatek: paris: bypass pinctrl GPIO layer in set GPIO direction
pinctrl_gpio_direction_input() / pinctrl_gpio_direction_output() take the pinctrl mutex. This causes a gpiochip operations to need to sleep. Worse yet, the .can_sleep field in the gpiochip is not set. This causes the shared GPIO proxy to trip over, as it uses gpiod_cansleep() to check whether it can use a spinlock or needs a mutex. In this case, it ends up taking a spinlock, then calls pinctrl_gpio_direction_output(), which takes a mutex. This causes a huge warning.
While this class of Mediatek hardware does not have separate clear/set registers, the pinctrl context has a spinlock that is taken whenever a register read-modify-write is done. Also, once the GPIO function is selected / muxed in, further GPIO operations do not involve pinctrl operations or state. The GPIO direction and level values do not require toggling the pinmux or any other pin config options.
Switch to directly calling mtk_pinmux_gpio_set_direction() in the GPIO set direction callbacks to avoid taking the pinctrl mutex. Drop the .gpio_set_direction field in mtk_pmxops to signal we are no longer using the pinctrl GPIO layer for setting the direction.
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