[PATCH v3] pinctrl: qcom: spmi-gpio: make direction changes exclusive

[Shawn Guo]

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.  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.

Open-drain and open-source outputs are the exception: such a pad only ever
drives one rail, so DIGITAL_INPUT_OUTPUT is physically correct for it, and
pmic_gpio_get() needs the input buffer to sample the line rather than
return the value last written.  Keep it enabled for those pads, and key
pmic_gpio_get_direction() off output_enabled so they still read back as
outputs.  gpiolib applies PIN_CONFIG_DRIVE_OPEN_DRAIN before calling
.direction_output(), so pad->buffer_type is up to date there.

An input must not drive the line whatever the buffer type, so
.direction_input() clears output_enabled unconditionally.

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 v3:
- .direction_output() clears PIN_CONFIG_INPUT_ENABLE only for
  PMIC_GPIO_OUT_BUF_CMOS pads; open-drain/open-source keep the input
  buffer so pmic_gpio_get() samples the wire.
- pmic_gpio_get_direction() now keys on output_enabled instead of
  input_enabled - required, or an open-drain output reports IN again and
  the -EPERM regression returns.
- Link to v2: https://lore.kernel.org/all/20260922065908.477523-1-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 | 35 ++++++++++++++++++------
 1 file changed, 27 insertions(+), 8 deletions(-)

diff --git a/drivers/pinctrl/qcom/pinctrl-spmi-gpio.c b/drivers/pinctrl/qcom/pinctrl-spmi-gpio.c
index f6dc43e27b38..dd9c212da6ee 100644
--- a/drivers/pinctrl/qcom/pinctrl-spmi-gpio.c
+++ b/drivers/pinctrl/qcom/pinctrl-spmi-gpio.c
@@ -734,29 +734,48 @@ static int pmic_gpio_get_direction(struct gpio_chip *chip, unsigned pin)
 	    (!pad->input_enabled && !pad->output_enabled))
 		return -EINVAL;
 
-	/* Make sure the state is aligned on what pmic_gpio_get() returns */
-	return pad->input_enabled ? GPIO_LINE_DIRECTION_IN : GPIO_LINE_DIRECTION_OUT;
+	/*
+	 * An open-drain or open-source pad keeps its input buffer enabled while
+	 * driving, so the output buffer is what tells the direction.
+	 */
+	return pad->output_enabled ? GPIO_LINE_DIRECTION_OUT : GPIO_LINE_DIRECTION_IN;
 }
 
 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;
+	struct pmic_gpio_pad *pad = state->ctrl->desc->pins[pin].drv_data;
+	unsigned long configs[2];
+	unsigned int nconfigs = 0;
 
-	config = pinconf_to_config_packed(PIN_CONFIG_LEVEL, val);
+	/*
+	 * An open-drain or open-source pad only ever drives one rail, so the
+	 * line can still be sampled while the pad is an output.  Leave the
+	 * input buffer enabled for those, so that pmic_gpio_get() reports what
+	 * is on the wire rather than the value last written.  gpiolib applies
+	 * PIN_CONFIG_DRIVE_OPEN_DRAIN before calling this, so buffer_type is
+	 * already up to date here.
+	 */
+	if (pad->buffer_type == PMIC_GPIO_OUT_BUF_CMOS)
+		configs[nconfigs++] =
+			pinconf_to_config_packed(PIN_CONFIG_INPUT_ENABLE, 0);
 
-	return pmic_gpio_config_set(state->ctrl, pin, &config, 1);
+	configs[nconfigs++] = pinconf_to_config_packed(PIN_CONFIG_LEVEL, val);
+
+	return pmic_gpio_config_set(state->ctrl, pin, configs, nconfigs);
 }
 
 static int pmic_gpio_get(struct gpio_chip *chip, unsigned pin)
-- 
2.43.0