Re: [PATCH v2] pinctrl: qcom: spmi-gpio: make direction changes exclusive

[Bartosz Golaszewski]

On Tue, 22 Sep 2026 08:59:08 +0200, Shawn Guo
<shengchao.guo@xxxxxxxxxxxxxxxx> said:
> pmic_gpio_populate() seeds pad->input_enabled and pad->output_enabled from
> the hardware MODE_CTL register, so a pad left in DIGITAL_INPUT or
> DIGITAL_INPUT_OUTPUT mode by the bootloader starts out with the input
> buffer enabled.  Neither direction callback clears the opposite buffer:
> .direction_output() only packs PIN_CONFIG_LEVEL, which sets
> output_enabled, and .direction_input() only packs PIN_CONFIG_INPUT_ENABLE,
> which sets input_enabled.  Requesting either direction on such a pad
> therefore programs MODE_DIGITAL_INPUT_OUTPUT rather than the requested
> direction.
>
> That silently breaks both directions.  After gpiod_direction_input() the
> pad keeps driving the line, since the output buffer is never disabled.
> And after gpiod_direction_output() pmic_gpio_get_direction() still reports
> GPIO_LINE_DIRECTION_IN, because it cannot tell plain input from
> input+output, which makes gpiolib consider the line an input while the
> driver is driving it.  On a board where several regulator-fixed nodes
> share one PMIC GPIO the shared GPIO proxy reads that direction back and
> rejects every consumer after the first:
>
>   reg-fixed-voltage regulator-wcn-core-vm-1p35: setup of GPIO (default) failed: -1
>   reg-fixed-voltage regulator-wcn-core-vm-1p35: error -EPERM: can't get GPIO
>
> Pack the opposite buffer's PIN_CONFIG_*_ENABLE along with the requested
> direction so that the resulting MODE_CTL is DIGITAL_INPUT or
> DIGITAL_OUTPUT, never both.  pmic_gpio_config_set() programs the registers
> once after walking all configs, so this stays a single register write.
>
> Pads that are genuinely bidirectional can still be described that way
> through pinconf, which is the interface that has always been able to
> express it; the gpiolib direction callbacks now mean what gpiolib says
> they mean.
>
> Fixes: 263447532463 ("pinctrl: qcom: spmi-gpio: implement .get_direction()")
> Assisted-by: LLM
> Signed-off-by: Shawn Guo <shengchao.guo@xxxxxxxxxxxxxxxx>
> ---
> Changes for v2:
> - Drop GPIO shared-proxy patch
> - Update Fixes tag (Thanks Neil!)
> - Link to v1: https://lore.kernel.org/all/20260915014447.282121-1-shengchao.guo@xxxxxxxxxxxxxxxx/
>
>  drivers/pinctrl/qcom/pinctrl-spmi-gpio.c | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/pinctrl/qcom/pinctrl-spmi-gpio.c b/drivers/pinctrl/qcom/pinctrl-spmi-gpio.c
> index f6dc43e27b38..eb4431591331 100644
> --- a/drivers/pinctrl/qcom/pinctrl-spmi-gpio.c
> +++ b/drivers/pinctrl/qcom/pinctrl-spmi-gpio.c
> @@ -741,22 +741,26 @@ static int pmic_gpio_get_direction(struct gpio_chip *chip, unsigned pin)
>  static int pmic_gpio_direction_input(struct gpio_chip *chip, unsigned pin)
>  {
>  	struct pmic_gpio_state *state = gpiochip_get_data(chip);
> -	unsigned long config;
> +	unsigned long configs[2];
>
> -	config = pinconf_to_config_packed(PIN_CONFIG_INPUT_ENABLE, 1);
> +	configs[0] = pinconf_to_config_packed(PIN_CONFIG_OUTPUT_ENABLE, 0);
> +	configs[1] = pinconf_to_config_packed(PIN_CONFIG_INPUT_ENABLE, 1);
>
> -	return pmic_gpio_config_set(state->ctrl, pin, &config, 1);
> +	return pmic_gpio_config_set(state->ctrl, pin, configs,
> +				    ARRAY_SIZE(configs));
>  }
>
>  static int pmic_gpio_direction_output(struct gpio_chip *chip,
>  				      unsigned pin, int val)
>  {
>  	struct pmic_gpio_state *state = gpiochip_get_data(chip);
> -	unsigned long config;
> +	unsigned long configs[2];
>
> -	config = pinconf_to_config_packed(PIN_CONFIG_LEVEL, val);
> +	configs[0] = pinconf_to_config_packed(PIN_CONFIG_INPUT_ENABLE, 0);

Sashiko's comment basically says that for open-drain GPIOs, if we set direction
to output via GPIOLIB and disable the input buffer, then later call
gpiod_get_value() on that GPIO, we'll never read what's really on the wire. Can
we not disable the input buffer for open-drain pins?

Bart