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>

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