sysreset: Add support for gpio-restart

The Linux kernel has binding for gpio-restart node.
This patch is adding basic support without supporting any optional
properties.
This driver was tested on Microblaze system where gpio is connected to
SoC reset logic.
Output value is handled via gpios cells values.

In gpio_reboot_request() set_value is writing 1 because
dm_gpio_set_value() is capable to changing it when it is ACTIVE_LOW.
...
	if (desc->flags & GPIOD_ACTIVE_LOW)
		value = !value;
...

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

MAINTAINERS

@@ -419,6 +419,7 @@ F:	drivers/net/xilinx_axi_emac.c
 F:	drivers/net/xilinx_emaclite.c
 F:	drivers/serial/serial_xuartlite.c
 F:	drivers/spi/xilinx_spi.c
+F:	drivers/sysreset/sysreset_gpio.c
 F:	drivers/watchdog/xilinx_tb_wdt.c
 N:	xilinx
 

drivers/sysreset/Kconfig

@@ -15,6 +15,14 @@ config SYSRESET
 
 if SYSRESET
 
+config SYSRESET_GPIO
+	bool "Enable support for GPIO reset driver"
+	select GPIO
+	help
+	  Reset support via GPIO pin connected reset logic. This is used for
+	  example on Microblaze where reset logic can be controlled via GPIO
+	  pin which triggers cpu reset.
+
 config SYSRESET_PSCI
 	bool "Enable support for PSCI System Reset"
 	depends on ARM_PSCI_FW

drivers/sysreset/Makefile

@@ -3,6 +3,7 @@
 # (C) Copyright 2016 Cadence Design Systems Inc.
 
 obj-$(CONFIG_SYSRESET) += sysreset-uclass.o
+obj-$(CONFIG_SYSRESET_GPIO) += sysreset_gpio.o
 obj-$(CONFIG_SYSRESET_PSCI) += sysreset_psci.o
 obj-$(CONFIG_SYSRESET_SYSCON) += sysreset_syscon.o
 obj-$(CONFIG_SYSRESET_WATCHDOG) += sysreset_watchdog.o

drivers/sysreset/sysreset_gpio.c

@@ -0,0 +1,59 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2018 Xilinx, Inc. - Michal Simek
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <sysreset.h>
+#include <asm/gpio.h>
+
+struct gpio_reboot_priv {
+	struct gpio_desc gpio;
+};
+
+static int gpio_reboot_request(struct udevice *dev, enum sysreset_t type)
+{
+	struct gpio_reboot_priv *priv = dev_get_priv(dev);
+
+	/*
+	 * When debug log is enabled please make sure that chars won't end up
+	 * in output fifo. Or you can append udelay(); to get enough time
+	 * to HW to emit output fifo.
+	 */
+	debug("GPIO reset\n");
+
+	/* Writing 1 respects polarity (active high/low) based on gpio->flags */
+	return dm_gpio_set_value(&priv->gpio, 1);
+}
+
+static struct sysreset_ops gpio_reboot_ops = {
+	.request = gpio_reboot_request,
+};
+
+int gpio_reboot_probe(struct udevice *dev)
+{
+	struct gpio_reboot_priv *priv = dev_get_priv(dev);
+
+	/*
+	 * Linux kernel DT binding contain others optional properties
+	 * which are not supported now
+	 */
+
+	return gpio_request_by_name(dev, "gpios", 0, &priv->gpio, GPIOD_IS_OUT);
+}
+
+static const struct udevice_id led_gpio_ids[] = {
+	{ .compatible = "gpio-restart" },
+	{ }
+};
+
+U_BOOT_DRIVER(gpio_reboot) = {
+	.id = UCLASS_SYSRESET,
+	.name = "gpio_restart",
+	.of_match = led_gpio_ids,
+	.ops = &gpio_reboot_ops,
+	.priv_auto_alloc_size = sizeof(struct gpio_reboot_priv),
+	.probe = gpio_reboot_probe,
+};