[RFC PATCH v3 2/3] mfd: rk8xx: Release the power hold GPIOs before powering off

[Yaozhong Li]

rk808_power_off() writes the PMIC's shutdown bit directly. On boards where
lines driven by the SoC gate the PMIC's power-off path, a shutdown
performed this way does not stick: the rails drop and immediately come
back up, so the board restarts instead of staying off. U-Boot reports the
result as a power-on reset.

Take those lines as an optional GPIO array, hold them asserted while the
system runs and release them - waiting power-hold-delay-ms - before
writing the shutdown bit. Device trees without the property retain the
existing behaviour.

The array is claimed before any child device is registered, so that a
-EPROBE_DEFER from the GPIO provider does not tear down the regulators,
RTC and clocks that devm_mfd_add_devices() has already registered.

On a Firefly-RK3399 the shutdown stuck when such a line went from high to
low before the shutdown bit was written, and did not when the line was
never driven.

Assisted-by: LLM
Signed-off-by: Yaozhong Li <yaozhonguwl at gmail.com>
---
 drivers/mfd/rk8xx-core.c  | 49 +++++++++++++++++++++++++++++++++++++--
 include/linux/mfd/rk808.h |  3 +++
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/rk8xx-core.c b/drivers/mfd/rk8xx-core.c
index 3dcf6ab..137ab20 100644
--- a/drivers/mfd/rk8xx-core.c
+++ b/drivers/mfd/rk8xx-core.c
@@ -11,6 +11,8 @@
  */
 
 #include <linux/bitfield.h>
+#include <linux/delay.h>
+#include <linux/gpio/consumer.h>
 #include <linux/interrupt.h>
 #include <linux/mfd/rk808.h>
 #include <linux/mfd/core.h>
@@ -703,6 +705,22 @@ static int rk808_power_off(struct sys_off_data *data)
 	default:
 		return NOTIFY_DONE;
 	}
+
+	/*
+	 * Some boards route "power hold" lines from the SoC into the board's
+	 * power circuitry. They have to be held asserted while the system is
+	 * running and released before the PMIC shutdown request is written,
+	 * otherwise the rails can drop and come back up instead of staying
+	 * off. Releasing them here rather than from a separate handler keeps
+	 * the ordering against the I2C write explicit.
+	 */
+	if (rk808->power_hold_gpios) {
+		for (unsigned int line = 0; line < rk808->power_hold_gpios->ndescs; line++)
+			gpiod_set_value_cansleep(rk808->power_hold_gpios->desc[line], 0);
+
+		msleep(rk808->power_hold_delay_ms);
+	}
+
 	ret = regmap_update_bits(rk808->regmap, reg, bit, bit);
 	if (ret)
 		dev_err(rk808->dev, "Failed to shutdown device!\n");
@@ -766,6 +784,7 @@ int rk8xx_probe(struct device *dev, int variant, unsigned int irq, struct regmap
 	struct rk808 *rk808;
 	const struct rk808_reg_data *pre_init_reg;
 	const struct mfd_cell *cells;
+	bool system_power_controller;
 	int dual_support = 0;
 	int nr_pre_init_regs;
 	u32 rst_fun = 0;
@@ -851,6 +870,33 @@ int rk8xx_probe(struct device *dev, int variant, unsigned int irq, struct regmap
 	if (!irq)
 		return dev_err_probe(dev, -EINVAL, "No interrupt support, no core IRQ\n");
 
+	system_power_controller =
+		device_property_read_bool(dev, "system-power-controller") ||
+		device_property_read_bool(dev, "rockchip,system-power-controller");
+
+	/*
+	 * Claim the optional power hold GPIOs before any child device is
+	 * registered. A -EPROBE_DEFER from the GPIO provider at this point
+	 * costs nothing, whereas deferring after devm_mfd_add_devices()
+	 * would tear the freshly registered children down again on every
+	 * retry.
+	 */
+	if (system_power_controller) {
+		rk808->power_hold_gpios = devm_gpiod_get_array_optional(dev, "power-hold",
+									GPIOD_OUT_HIGH);
+		if (IS_ERR(rk808->power_hold_gpios))
+			return dev_err_probe(dev, PTR_ERR(rk808->power_hold_gpios),
+					     "Failed to get power hold GPIOs\n");
+
+		/*
+		 * The settle time is optional. rk808 is zero initialised and
+		 * the binding documents 0 as the default, so an absent property
+		 * means the shutdown request follows the release with no wait.
+		 */
+		device_property_read_u32(dev, "power-hold-delay-ms",
+					 &rk808->power_hold_delay_ms);
+	}
+
 	ret = devm_regmap_add_irq_chip(dev, rk808->regmap, irq,
 				       IRQF_ONESHOT | dual_support, -1,
 				       rk808->regmap_irq_chip, &rk808->irq_data);
@@ -872,8 +918,7 @@ int rk8xx_probe(struct device *dev, int variant, unsigned int irq, struct regmap
 	if (ret)
 		return dev_err_probe(dev, ret, "failed to add MFD devices\n");
 
-	if (device_property_read_bool(dev, "system-power-controller") ||
-	    device_property_read_bool(dev, "rockchip,system-power-controller")) {
+	if (system_power_controller) {
 		ret = devm_register_sys_off_handler(dev,
 				    SYS_OFF_MODE_POWER_OFF_PREPARE, SYS_OFF_PRIO_HIGH,
 				    &rk808_power_off, rk808);
diff --git a/include/linux/mfd/rk808.h b/include/linux/mfd/rk808.h
index 7ffc904..e56d595 100644
--- a/include/linux/mfd/rk808.h
+++ b/include/linux/mfd/rk808.h
@@ -15,6 +15,7 @@
 #ifndef __LINUX_REGULATOR_RK808_H
 #define __LINUX_REGULATOR_RK808_H
 
+#include <linux/gpio/consumer.h>
 #include <linux/regulator/machine.h>
 #include <linux/regmap.h>
 
@@ -1466,6 +1467,8 @@ struct rk808 {
 	long				variant;
 	const struct regmap_config	*regmap_cfg;
 	const struct regmap_irq_chip	*regmap_irq_chip;
+	struct gpio_descs		*power_hold_gpios;
+	u32				power_hold_delay_ms;
 };
 
 void rk8xx_shutdown(struct device *dev);
-- 
2.55.0.windows.3