firmware: raspberrypi: notify VC4 firmware of a reboot

The firmware-owned GPIO expander on RPi 3 B+ must be in same state
after a reboot as initial power on. Otherwise this would cause a
network boot failure of the BOOTROM. So inform the VC4 firmware to restore
the expander before doing a reboot.
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Tested-by: Phil Elwell <phil@raspberrypi.org>
Reviewed-by: Eric Anholt <eric@anholt.net>

drivers/firmware/raspberrypi.c

@@ -238,6 +238,16 @@ static int rpi_firmware_probe(struct platform_device *pdev)
 	return 0;
 }
 
+static void rpi_firmware_shutdown(struct platform_device *pdev)
+{
+	struct rpi_firmware *fw = platform_get_drvdata(pdev);
+
+	if (!fw)
+		return;
+
+	rpi_firmware_property(fw, RPI_FIRMWARE_NOTIFY_REBOOT, NULL, 0);
+}
+
 static int rpi_firmware_remove(struct platform_device *pdev)
 {
 	struct rpi_firmware *fw = platform_get_drvdata(pdev);
@@ -278,6 +288,7 @@ static struct platform_driver rpi_firmware_driver = {
 		.of_match_table = rpi_firmware_of_match,
 	},
 	.probe		= rpi_firmware_probe,
+	.shutdown	= rpi_firmware_shutdown,
 	.remove		= rpi_firmware_remove,
 };
 module_platform_driver(rpi_firmware_driver);