dm: Add support for generic system controllers (syscon)

Many SoCs have a number of system controllers which are dealt with as a
group by a single driver. It is a pain to have to add lots of compatible
strings and/or separate drivers for each. Instead we can identify the
controllers by a number and request the address of the one we want.

Add a simple implementation of this which can be used by SoC driver code.

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

drivers/core/syscon-uclass.c

@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2015 Google, Inc
+ * Written by Simon Glass <sjg@chromium.org>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+#include <common.h>
+#include <syscon.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>
+
+struct regmap *syscon_get_regmap(struct udevice *dev)
+{
+	struct syscon_uc_info *priv = dev_get_uclass_priv(dev);
+
+	return priv->regmap;
+}
+
+static int syscon_pre_probe(struct udevice *dev)
+{
+	struct syscon_uc_info *priv = dev_get_uclass_priv(dev);
+
+	return regmap_init_mem(dev, &priv->regmap);
+}
+
+struct regmap *syscon_get_regmap_by_driver_data(ulong driver_data)
+{
+	struct udevice *dev;
+	struct uclass *uc;
+	int ret;
+
+	ret = uclass_get(UCLASS_SYSCON, &uc);
+	if (ret)
+		return ERR_PTR(ret);
+	uclass_foreach_dev(dev, uc) {
+		if (dev->driver_data == driver_data) {
+			struct syscon_uc_info *priv;
+			int ret;
+
+			ret = device_probe(dev);
+			if (ret)
+				return ERR_PTR(ret);
+			priv = dev_get_uclass_priv(dev);
+
+			return priv->regmap;
+		}
+	}
+
+	return ERR_PTR(-ENOENT);
+}
+
+void *syscon_get_first_range(ulong driver_data)
+{
+	struct regmap *map;
+
+	map = syscon_get_regmap_by_driver_data(driver_data);
+	if (IS_ERR(map))
+		return map;
+	return regmap_get_range(map, 0);
+}
+
+UCLASS_DRIVER(syscon) = {
+	.id		= UCLASS_SYSCON,
+	.name		= "syscon",
+	.per_device_auto_alloc_size = sizeof(struct syscon_uc_info),
+	.pre_probe = syscon_pre_probe,
+};