dm: Add a system reset uclass

It is common for system reset to be available at multiple levels in modern
hardware. For example, an SoC may provide a reset option, and a board may
provide its own reset for reasons of security or thoroughness. It is useful
to be able to model this hardware without hard-coding the behaviour in the
SoC or board. Also there is a distinction sometimes between resetting just
the CPU (leaving GPIO state alone) and resetting all the PMICs, just cutting
power.

To achieve this, add a simple system reset uclass. It allows multiple devices
to provide reset functionality and provides a way to walk through them,
requesting a particular reset type until is it provided.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/misc/Kconfig

@@ -73,3 +73,12 @@ config PCA9551_I2C_ADDR
 	default 0x60
 	help
 	  The I2C address of the PCA9551 LED controller.
+
+config RESET
+	bool "Enable support for reset drivers"
+	depends on DM
+	help
+	  Enable reset drivers which can be used to reset the CPU or board.
+	  Each driver can provide a reset method which will be called to
+	  effect a reset. The uclass will try all available drivers when
+	  reset_walk() is called.

drivers/misc/Makefile

@@ -32,3 +32,4 @@ obj-$(CONFIG_TWL4030_LED) += twl4030_led.o
 obj-$(CONFIG_FSL_IFC) += fsl_ifc.o
 obj-$(CONFIG_FSL_SEC_MON) += fsl_sec_mon.o
 obj-$(CONFIG_PCA9551_LED) += pca9551_led.o
+obj-$(CONFIG_RESET) += reset-uclass.o

drivers/misc/reset-uclass.c

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <reset.h>
+#include <dm.h>
+#include <errno.h>
+#include <regmap.h>
+#include <dm/device-internal.h>
+#include <dm/lists.h>
+#include <dm/root.h>
+#include <linux/err.h>
+
+int reset_request(struct udevice *dev, enum reset_t type)
+{
+	struct reset_ops *ops = reset_get_ops(dev);
+
+	if (!ops->request)
+		return -ENOSYS;
+
+	return ops->request(dev, type);
+}
+
+void reset_walk(enum reset_t type)
+{
+	struct udevice *dev;
+	int ret = 0;
+
+	while (ret != -EINPROGRESS && type < RESET_COUNT) {
+		for (uclass_first_device(UCLASS_RESET, &dev);
+		dev;
+		uclass_next_device(&dev)) {
+			ret = reset_request(dev, type);
+			if (ret == -EINPROGRESS)
+				break;
+		}
+	}
+
+	/* Wait for the reset to take effect */
+	mdelay(100);
+
+	/* Still no reset? Give up */
+	printf("Reset not supported on this platform\n");
+	hang();
+}
+
+/**
+ * reset_cpu() - calls reset_walk(RESET_WARM)
+ */
+void reset_cpu(ulong addr)
+{
+	reset_walk(RESET_WARM);
+}
+
+UCLASS_DRIVER(reset) = {
+	.id		= UCLASS_RESET,
+	.name		= "reset",
+};

include/dm/uclass-id.h

@@ -44,6 +44,7 @@ enum uclass_id {
 	UCLASS_PCI_GENERIC,	/* Generic PCI bus device */
 	UCLASS_PMIC,		/* PMIC I/O device */
 	UCLASS_REGULATOR,	/* Regulator device */
+	UCLASS_RESET,		/* Reset device */
 	UCLASS_RTC,		/* Real time clock device */
 	UCLASS_SERIAL,		/* Serial UART */
 	UCLASS_SPI,		/* SPI bus */

include/reset.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright (c) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#ifndef __RESET_H
+#define __RESET_H
+
+enum reset_t {
+	RESET_WARM,	/* Reset CPU, keep GPIOs active */
+	RESET_COLD,	/* Reset CPU and GPIOs */
+	RESET_POWER,	/* Reset PMIC (remove and restore power) */
+
+	RESET_COUNT,
+};
+
+struct reset_ops {
+	/**
+	 * request() - request a reset of the given type
+	 *
+	 * Note that this function may return before the reset takes effect.
+	 *
+	 * @type:	Reset type to request
+	 * @return -EINPROGRESS if the reset has been started and
+	 *		will complete soon, -EPROTONOSUPPORT if not supported
+	 *		by this device, 0 if the reset has already happened
+	 *		(in which case this method will not actually return)
+	 */
+	int (*request)(struct udevice *dev, enum reset_t type);
+};
+
+#define reset_get_ops(dev)        ((struct reset_ops *)(dev)->driver->ops)
+
+/**
+ * reset_request() - request a reset
+ *
+ * @type:	Reset type to request
+ * @return 0 if OK, -EPROTONOSUPPORT if not supported by this device
+ */
+int reset_request(struct udevice *dev, enum reset_t type);
+
+/**
+ * reset_walk() - cause a reset
+ *
+ * This works through the available reset devices until it finds one that can
+ * perform a reset. If the provided reset type is not available, the next one
+ * will be tried.
+ *
+ * If this function fails to reset, it will display a message and halt
+ *
+ * @type:	Reset type to request
+ */
+void reset_walk(enum reset_t type);
+
+/**
+ * reset_cpu() - calls reset_walk(RESET_WARM)
+ */
+void reset_cpu(ulong addr);
+
+#endif