When restarting a CPU powered by the PCA9450 power management IC, it
is beneficial to use the PCA9450 to power cycle the CPU and all its
connected peripherals to start up in a known state. The PCA9450 features
a cold start procedure initiated by an I2C command.

Add a restart handler so that the PCA9450 is used to restart the CPU.
The restart handler sends command 0x14 to the SW_RST register,
initiating a cold reset (Power recycle all regulators except LDO1, LDO2
and CLK_32K_OUT)

As the PCA9450 is a PMIC specific for the i.MX8M family CPU, the restart
handler priority is set just slightly higher than imx2_wdt and the PSCI
restart handler. This makes sure this restart handler takes precedence.

Signed-off-by: Paul Geurts <paul.geurts@prodrive-technologies.com>
---
 drivers/regulator/pca9450-regulator.c | 27 +++++++++++++++++++++++++++
 include/linux/regulator/pca9450.h     |  5 +++++
 2 files changed, 32 insertions(+)

diff --git a/drivers/regulator/pca9450-regulator.c b/drivers/regulator/pca9450-regulator.c
index a56f3ab754fa..14d19a6d6655 100644
--- a/drivers/regulator/pca9450-regulator.c
+++ b/drivers/regulator/pca9450-regulator.c
@@ -9,6 +9,7 @@
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
+#include <linux/reboot.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
@@ -33,6 +34,7 @@ struct pca9450 {
 	struct device *dev;
 	struct regmap *regmap;
 	struct gpio_desc *sd_vsel_gpio;
+	struct notifier_block restart_nb;
 	enum pca9450_chip_type type;
 	unsigned int rcnt;
 	int irq;
@@ -965,6 +967,25 @@ static irqreturn_t pca9450_irq_handler(int irq, void *data)
 	return IRQ_HANDLED;
 }
 
+static int pca9450_i2c_restart_handler(struct notifier_block *nb,
+				unsigned long action, void *data)
+{
+	struct pca9450 *pca9450 = container_of(nb, struct pca9450, restart_nb);
+	struct i2c_client *i2c = container_of(pca9450->dev, struct i2c_client, dev);
+
+	dev_dbg(&i2c->dev, "Restarting device..\n");
+	if (i2c_smbus_write_byte_data(i2c, PCA9450_REG_SWRST, SW_RST_COMMAND) == 0) {
+		/* tRESTART is 250ms, so 300 should be enough to make sure it happened */
+		mdelay(300);
+		/* When we get here, the PMIC didn't power cycle for some reason. so warn.*/
+		dev_warn(&i2c->dev, "Device didn't respond to restart command\n");
+	} else {
+		dev_err(&i2c->dev, "Restart command failed\n");
+	}
+
+	return 0;
+}
+
 static int pca9450_i2c_probe(struct i2c_client *i2c)
 {
 	enum pca9450_chip_type type = (unsigned int)(uintptr_t)
@@ -1107,6 +1128,12 @@ static int pca9450_i2c_probe(struct i2c_client *i2c)
 	pca9450->sd_vsel_fixed_low =
 		of_property_read_bool(ldo5->dev.of_node, "nxp,sd-vsel-fixed-low");
 
+	pca9450->restart_nb.notifier_call = pca9450_i2c_restart_handler;
+	pca9450->restart_nb.priority = PCA9450_RESTART_HANDLER_PRIORITY;
+
+	if (register_restart_handler(&pca9450->restart_nb))
+		dev_warn(&i2c->dev, "Failed to register restart handler\n");
+
 	dev_info(&i2c->dev, "%s probed.\n",
 		type == PCA9450_TYPE_PCA9450A ? "pca9450a" :
 		(type == PCA9450_TYPE_PCA9451A ? "pca9451a" : "pca9450bc"));
diff --git a/include/linux/regulator/pca9450.h b/include/linux/regulator/pca9450.h
index b427b5873de1..85b4fecc10d8 100644
--- a/include/linux/regulator/pca9450.h
+++ b/include/linux/regulator/pca9450.h
@@ -35,6 +35,8 @@ enum {
 	PCA9450_DVS_LEVEL_MAX,
 };
 
+#define PCA9450_RESTART_HANDLER_PRIORITY 130
+
 #define PCA9450_BUCK1_VOLTAGE_NUM	0x80
 #define PCA9450_BUCK2_VOLTAGE_NUM	0x80
 #define PCA9450_BUCK3_VOLTAGE_NUM	0x80
@@ -235,4 +237,7 @@ enum {
 #define I2C_LT_ON_RUN			0x02
 #define I2C_LT_FORCE_ENABLE		0x03
 
+/* PCA9450_REG_SW_RST command */
+#define SW_RST_COMMAND			0x14
+
 #endif /* __LINUX_REG_PCA9450_H__ */
-- 
2.39.2

On Mon, 05 May 2025 13:59:36 +0200, Paul Geurts wrote:
> When restarting a CPU powered by the PCA9450 power management IC, it
> is beneficial to use the PCA9450 to power cycle the CPU and all its
> connected peripherals to start up in a known state. The PCA9450 features
> a cold start procedure initiated by an I2C command.
> 
> Add a restart handler so that the PCA9450 is used to restart the CPU.
> The restart handler sends command 0x14 to the SW_RST register,
> initiating a cold reset (Power recycle all regulators except LDO1, LDO2
> and CLK_32K_OUT)
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator.git for-next

Thanks!

[1/1] regulator: pca9450: Add restart handler
      commit: 6157e62b07d9331cc1d4d9d525dab33d45b0e83c

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark