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/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",
+};