mfd: tps6586x: Register restart handler

There are a couple of boards which use a tps6586x as
"ti,system-power-controller", e.g. the tegra20-tamonten.dtsi.
For these, the only registered restart handler is the warm reboot via
tegra's PMC. As the bootloader of the tegra20 requires the VDE, it must
be ensured that VDE is enabled (which is the case after a cold reboot).
For the "normal reboot", this is basically the case since 8f0c714a.
However, this workaround is not executed in case of an emergency restart.
In case of an emergency restart, the system now simply hangs in the
bootloader, as VDE is not enabled (because it is not used).

The TPS658629-Q1 provides a SOFT RST bit in the SUPPLYENE reg to request
a (cold) reboot, which takes at least 20ms (as the data sheet states).
This avoids the hang-up.

Tested on a TPS658640.
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Benjamin Bara <benjamin.bara@skidata.com>
Link: https://lore.kernel.org/r/20230327-tegra-pmic-reboot-v7-5-18699d5dcd76@skidata.comSigned-off-by: Lee Jones <lee@kernel.org>

drivers/mfd/tps6586x.c

@@ -30,6 +30,7 @@
 #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)
 
@@ -475,6 +476,19 @@ static int tps6586x_power_off_handler(struct sys_off_data *data)
 	return notifier_from_errno(-ETIME);
 }
 
+static int tps6586x_restart_handler(struct sys_off_data *data)
+{
+	int ret;
+
+	/* Put the PMIC into hard reboot state. This takes at least 20ms. */
+	ret = tps6586x_set_bits(data->dev, TPS6586X_SUPPLYENE, SOFT_RST_BIT);
+	if (ret)
+		return notifier_from_errno(ret);
+
+	mdelay(50);
+	return notifier_from_errno(-ETIME);
+}
+
 static void tps6586x_print_version(struct i2c_client *client, int version)
 {
 	const char *name;
@@ -575,6 +589,13 @@ static int tps6586x_i2c_probe(struct i2c_client *client)
 			dev_err(&client->dev, "register power off handler failed: %d\n", ret);
 			goto err_add_devs;
 		}
+
+		ret = devm_register_restart_handler(&client->dev, &tps6586x_restart_handler,
+						    NULL);
+		if (ret) {
+			dev_err(&client->dev, "register restart handler failed: %d\n", ret);
+			goto err_add_devs;
+		}
 	}
 
 	return 0;