[PATCH] mfd: tps6586x: register restart handler

[Benjamin Bara <bbara93@gmail.com>]

From: Benjamin Bara <benjamin.bara@skidata.com>

The TPS658629-Q1 (unfortunately the only TPS6586x with public data sheet)
provides a SOFT RST bit in the SUPPLYENE reg to request a (cold) reboot.

Use it to implement and register a restart handler/notifier.
The DS does not clarify if only writing the SOFT RST bit has side effects.
Therefore, regmap_update_bits() is used.

Set an appropriate system_state and disable the IRQs to activate
i2c_in_atomic_xfer_mode(). This avoids the following WARNING:
[   12.667612] WARNING: CPU: 1 PID: 1 at kernel/rcu/tree_plugin.h:318 rcu_note_context_switch+0x33c/0x6b0
[   12.676926] Voluntary context switch within RCU read-side critical section!
...
[   12.742376]  schedule_timeout from wait_for_completion_timeout+0x90/0x114
[   12.749179]  wait_for_completion_timeout from tegra_i2c_wait_completion+0x40/0x70

Tested on a TPS658640.

Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
---
 drivers/mfd/tps6586x.c | 38 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/drivers/mfd/tps6586x.c b/drivers/mfd/tps6586x.c
index 2d947f3f606a..e40c664b5f64 100644
--- a/drivers/mfd/tps6586x.c
+++ b/drivers/mfd/tps6586x.c
@@ -15,6 +15,7 @@
 #include <linux/interrupt.h>
 #include <linux/irq.h>
 #include <linux/irqdomain.h>
+#include <linux/irqflags.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
@@ -22,6 +23,7 @@
 #include <linux/err.h>
 #include <linux/i2c.h>
 #include <linux/platform_device.h>
+#include <linux/reboot.h>
 #include <linux/regmap.h>
 #include <linux/of.h>
 
@@ -29,6 +31,7 @@
 #include <linux/mfd/tps6586x.h>
 
 #define TPS6586X_SUPPLYENE	0x14
+#define SOFT_RST_BIT		BIT(0)
 #define EXITSLREQ_BIT		BIT(1)
 #define SLEEP_MODE_BIT		BIT(3)
 
@@ -466,6 +469,23 @@ static void tps6586x_power_off(void)
 	tps6586x_set_bits(tps6586x_dev, TPS6586X_SUPPLYENE, SLEEP_MODE_BIT);
 }
 
+static int tps6586x_restart_notify(struct notifier_block *this, unsigned long mode, void *data)
+{
+	/* bring pmic into HARD REBOOT state, disable IRQs for atomic i2c RCU */
+	system_state = SYSTEM_RESTART;
+	local_irq_disable();
+	tps6586x_set_bits(tps6586x_dev, TPS6586X_SUPPLYENE, SOFT_RST_BIT);
+	local_irq_enable();
+
+	mdelay(500);
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block tps6586x_restart_handler = {
+	.notifier_call = tps6586x_restart_notify,
+	.priority = 200,
+};
+
 static void tps6586x_print_version(struct i2c_client *client, int version)
 {
 	const char *name;
@@ -559,9 +579,16 @@ static int tps6586x_i2c_probe(struct i2c_client *client)
 		goto err_add_devs;
 	}
 
-	if (pdata->pm_off && !pm_power_off) {
+	if (pdata->pm_off) {
 		tps6586x_dev = &client->dev;
-		pm_power_off = tps6586x_power_off;
+		if (!pm_power_off)
+			pm_power_off = tps6586x_power_off;
+
+		ret = register_restart_handler(&tps6586x_restart_handler);
+		if (ret) {
+			dev_err(&client->dev, "register restart handler failed: %d\n", ret);
+			goto err_add_devs;
+		}
 	}
 
 	return 0;
@@ -582,6 +609,13 @@ static void tps6586x_i2c_remove(struct i2c_client *client)
 	mfd_remove_devices(tps6586x->dev);
 	if (client->irq)
 		free_irq(client->irq, tps6586x);
+
+	if (tps6586x_dev == &client->dev) {
+		tps6586x_dev = NULL;
+		unregister_restart_handler(&tps6586x_restart_handler);
+		if (pm_power_off == tps6586x_power_off)
+			pm_power_off = NULL;
+	}
 }
 
 static int __maybe_unused tps6586x_i2c_suspend(struct device *dev)
-- 
2.34.1