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

[Yaozhong Li <yaozhonguwl@gmail.com>]

rk808_power_off() writes the PMIC's shutdown bit directly. On boards with
"power hold" lines driven by the SoC, 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.

Releasing every described line matters: on a Firefly-RK3399 the board
stays off when both lines described for it are released, whereas releasing
GPIO1_D0 while GPIO1_B5 is left asserted makes it come back up.

Signed-off-by: Yaozhong Li <yaozhonguwl@gmail.com>
---
 drivers/mfd/rk8xx-core.c  | 29 +++++++++++++++++++++++++++++
 include/linux/mfd/rk808.h |  4 ++++
 2 files changed, 33 insertions(+)

diff --git a/drivers/mfd/rk8xx-core.c b/drivers/mfd/rk8xx-core.c
index 3dcf6ab..fd1efbb 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 +705,24 @@ 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:
+	 * with any of them left asserted, the rails drop and then come back
+	 * up. Releasing them here rather than from a separate handler keeps
+	 * the ordering against the I2C write explicit.
+	 */
+	if (rk808->power_hold_gpios) {
+		unsigned int i;
+
+		for (i = 0; i < rk808->power_hold_gpios->ndescs; i++)
+			gpiod_set_value_cansleep(rk808->power_hold_gpios->desc[i], 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");
@@ -874,6 +894,15 @@ int rk8xx_probe(struct device *dev, int variant, unsigned int irq, struct regmap
 
 	if (device_property_read_bool(dev, "system-power-controller") ||
 	    device_property_read_bool(dev, "rockchip,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");
+
+		device_property_read_u32(dev, "power-hold-delay-ms",
+					 &rk808->power_hold_delay_ms);
+
 		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..eda111e 100644
--- a/include/linux/mfd/rk808.h
+++ b/include/linux/mfd/rk808.h
@@ -1459,6 +1459,8 @@ enum {
 	RK818_ID = 0x8180,
 };
 
+struct gpio_descs;
+
 struct rk808 {
 	struct device			*dev;
 	struct regmap_irq_chip_data	*irq_data;
@@ -1466,6 +1468,8 @@ 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