microblaze: Switch to standard restart handler

The microblaze uses the legacy APIs to dig out a GPIO pin
defined in the root of the device tree to issue a hard
reset of the platform.

Asserting a hard reset should be done using the standard
DT-enabled and fully GPIO descriptor aware driver in
drivers/power/reset/gpio-restart.c using the bindings
from Documentation/devicetree/bindings/power/reset/gpio-restart.txt

To achieve this, first make sure microblaze makes use of
the standard kernel restart path utilizing do_kernel_restart()
from <linux/reboot.h>. Put in some grace time and an
emergency print if the restart does not properly assert.

As this is basic platform functionality we patch the DTS
file and defconfig in one go for a lockstep change.

Cc: Arnd Bergmann <[e-mail]>
Cc: Michal Simek <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>
[ Michal: Move machine_restart back to reset.c ]
Signed-off-by: Michal Simek <[e-mail]>

arch/microblaze/boot/dts/system.dts

···
 	#address-cells = <1>;
 	#size-cells = <1>;
 	compatible = "xlnx,microblaze";
-	hard-reset-gpios = <&LEDs_8Bit 2 1>;
 	model = "testing";
 	DDR2_SDRAM: memory@90000000 {
 		device_type = "memory";
···
 				gpios = <&LEDs_8Bit 7 1>;
 			};
 		} ;
+
+		gpio-restart {
+			compatible = "gpio-restart";
+			/*
+			 * FIXME: is this active low or active high?
+			 * the current flag (1) indicates active low.
+			 * delay measures are templates, should be adjusted
+			 * to datasheet or trial-and-error with real hardware.
+			 */
+			gpios = <&LEDs_8Bit 2 1>;
+			active-delay = <100>;
+			inactive-delay = <10>;
+			wait-delay = <100>;
+		};
+
 		RS232_Uart_1: serial@84000000 {
 			clock-frequency = <125000000>;
 			compatible = "xlnx,xps-uartlite-1.00.a";

arch/microblaze/configs/mmu_defconfig

···
 CONFIG_GPIOLIB=y
 CONFIG_GPIO_SYSFS=y
 CONFIG_GPIO_XILINX=y
+CONFIG_POWER_RESET=y
+CONFIG_POWER_RESET_GPIO_RESTART=y
 # CONFIG_HWMON is not set
 CONFIG_WATCHDOG=y
 CONFIG_XILINX_WATCHDOG=y

arch/microblaze/configs/nommu_defconfig

···
 CONFIG_GPIOLIB=y
 CONFIG_GPIO_SYSFS=y
 CONFIG_GPIO_XILINX=y
+CONFIG_POWER_RESET=y
+CONFIG_POWER_RESET_GPIO_RESTART=y
 # CONFIG_HWMON is not set
 CONFIG_WATCHDOG=y
 CONFIG_XILINX_WATCHDOG=y

arch/microblaze/kernel/reset.c

···
  */
 
 #include <linux/init.h>
+#include <linux/delay.h>
 #include <linux/of_platform.h>
-
-/* Trigger specific functions */
-#ifdef CONFIG_GPIOLIB
-
-#include <linux/of_gpio.h>
-
-static int handle; /* reset pin handle */
-static unsigned int reset_val;
-
-static int of_platform_reset_gpio_probe(void)
-{
-	int ret;
-	handle = of_get_named_gpio(of_find_node_by_path("/"),
-				   "hard-reset-gpios", 0);
-
-	if (!gpio_is_valid(handle)) {
-		pr_info("Skipping unavailable RESET gpio %d (%s)\n",
-				handle, "reset");
-		return -ENODEV;
-	}
-
-	ret = gpio_request(handle, "reset");
-	if (ret < 0) {
-		pr_info("GPIO pin is already allocated\n");
-		return ret;
-	}
-
-	/* get current setup value */
-	reset_val = gpio_get_value(handle);
-	/* FIXME maybe worth to perform any action */
-	pr_debug("Reset: Gpio output state: 0x%x\n", reset_val);
-
-	/* Setup GPIO as output */
-	ret = gpio_direction_output(handle, 0);
-	if (ret < 0)
-		goto err;
-
-	/* Setup output direction */
-	gpio_set_value(handle, 0);
-
-	pr_info("RESET: Registered gpio device: %d, current val: %d\n",
-							handle, reset_val);
-	return 0;
-err:
-	gpio_free(handle);
-	return ret;
-}
-device_initcall(of_platform_reset_gpio_probe);
-
-
-static void gpio_system_reset(void)
-{
-	if (gpio_is_valid(handle))
-		gpio_set_value(handle, 1 - reset_val);
-	else
-		pr_notice("Reset GPIO unavailable - halting!\n");
-}
-#else
-static void gpio_system_reset(void)
-{
-	pr_notice("No reset GPIO present - halting!\n");
-}
-
-void of_platform_reset_gpio_probe(void)
-{
-	return;
-}
-#endif
-
-void machine_restart(char *cmd)
-{
-	pr_notice("Machine restart...\n");
-	gpio_system_reset();
-	while (1)
-		;
-}
+#include <linux/reboot.h>
 
 void machine_shutdown(void)
 {
···
 	pr_notice("Machine power off...\n");
 	while (1)
 		;
+}
+
+void machine_restart(char *cmd)
+{
+	do_kernel_restart(cmd);
+	/* Give the restart hook 1 s to take us down */
+	mdelay(1000);
+	pr_emerg("Reboot failed -- System halted\n");
+	while (1);
 }