mtd: add mtdram device (which build mtd over ram area - useful for FRAM oder MRAM)

Change since v1 (Sascha, thanks for review):
	* use xzalloc instead of kzalloc and control check
	* correct help and names
	* fix coding style issue
	* remove verbose and unneeded messages

This adds support for MTD in RAM devices (like FRAM or MRAM).

Signed-off-by: Sebastian Block <basti@linux-source.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

drivers/mtd/devices/Kconfig

@@ -58,4 +58,9 @@ config MTD_DOCG3
 	  M-Systems and now Sandisk. The support is very experimental,
 	  and doesn't give access to any write operations.
 
+config MTD_MTDRAM
+	tristate "Support for NVRAM devices (FRAM, MRAM, ...)"
+	help
+	  This enables non volatile RAM to used as MTD devices.
+
 endmenu

drivers/mtd/devices/Makefile

@@ -5,3 +5,4 @@
 obj-$(CONFIG_MTD_DATAFLASH)	+= mtd_dataflash.o
 obj-$(CONFIG_MTD_DOCG3)		+= docg3.o
 obj-$(CONFIG_MTD_M25P80)	+= m25p80.o
+obj-$(CONFIG_MTD_MTDRAM)	+= mtdram.o

drivers/mtd/devices/mtdram.c

@@ -0,0 +1,122 @@
+/*
+ * Author: Sebastian Block <basti@linux-source.de>
+ * Copyright (c) 2014
+ *
+ * Some parts are based on mtdram.c found in Linux kernel
+ * by   Alexander Larsson <alex@cendio.se>
+ * and  Joern Engel <joern@wh.fh-wedel.de>.
+ *
+ * This code is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ */
+#include <common.h>
+#include <environment.h>
+#include <errno.h>
+#include <init.h>
+#include <io.h>
+#include <linux/mtd/mtd.h>
+#include <malloc.h>
+#include <of.h>
+
+struct mtdram_priv_data {
+	struct mtd_info mtd;
+	void *base;
+};
+
+static int ram_erase(struct mtd_info *mtd, struct erase_info *instr)
+{
+	memset((char *)mtd->priv + instr->addr, 0xff, instr->len);
+	instr->state = MTD_ERASE_DONE;
+	mtd_erase_callback(instr);
+	return 0;
+}
+
+static int ram_write(struct mtd_info *mtd, loff_t to, size_t len, size_t *retlen, const u_char *buf)
+{
+	memcpy((char*)mtd->priv + to, buf, len);
+	*retlen = len;
+	return 0;
+}
+
+static int ram_read(struct mtd_info *mtd, loff_t from, size_t len, size_t *retlen, u_char *buf)
+{
+	memcpy(buf, mtd->priv + from, len);
+	*retlen = len;
+	return 0;
+}
+
+static int mtdram_probe(struct device_d *dev)
+{
+	void __iomem *base;
+	int device_id;
+	struct mtd_info *mtd;
+	struct resource *res;
+	loff_t size;
+	int ret = 0;
+
+	mtd = xzalloc(sizeof(struct mtd_info));
+
+	device_id = DEVICE_ID_SINGLE;
+	if (dev->device_node) {
+		const char *alias = of_alias_get(dev->device_node);
+		if (alias)
+			mtd->name = xstrdup(alias);
+	}
+
+	if (!mtd->name) {
+		device_id = DEVICE_ID_DYNAMIC;
+		mtd->name = "mtdram";
+	}
+
+	base = dev_request_mem_region(dev, 0);
+	if (!base) {
+		ret = -EBUSY;
+		goto nobase;
+	}
+
+	res = dev_get_resource(dev, IORESOURCE_MEM, 0);
+	size = (unsigned long) resource_size(res);
+	mtd->priv = base;
+
+	mtd->type = MTD_RAM;
+	mtd->writesize = 1;
+	mtd->writebufsize = 64;
+	mtd->flags = MTD_CAP_RAM;
+	mtd->size = size;
+
+	mtd->read = ram_read;
+	mtd->write = ram_write;
+	mtd->erase = ram_erase;
+	mtd->erasesize = 1;
+
+	mtd->parent = dev;
+
+	ret = add_mtd_device(mtd, mtd->name, device_id);
+	return ret;
+
+nobase:
+	kfree(mtd);
+
+	return ret;
+}
+
+static __maybe_unused struct of_device_id mtdram_dt_ids[] = {
+	{
+		.compatible	= "mtd-ram",
+	}, {
+		/*  sentinel */
+	}
+};
+
+static struct driver_d mtdram_driver = {
+	.name	= "mtdram",
+	.probe	= mtdram_probe,
+	.of_compatible	= DRV_OF_COMPAT(mtdram_dt_ids),
+};
+device_platform_driver(mtdram_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Sebastian Block");
+MODULE_DESCRIPTION("MTD RAM driver for NVRAMs");