Revert "mtd: maps: remove uclinux map driver"

The uclinux MTD map driver is still actively used on ColdFire (m68k)
platforms. The ColdFire startup code in arch/m68k/coldfire/head.S copies
an attached filesystem blob to _bss_stop, and the uclinux driver picks
it up from there. Most ColdFire defconfigs enable CONFIG_MTD_UCLINUX, as
the driver seems to serve as a replacement for CONFIG_BLK_DEV_INITRD on
these non-MMU targets.

The driver was removed as part of a series cleaning up AMD Élan specific
drivers, but unlike the other three drivers in that series, this driver
seemed to not be as Élan specific (nor unused) as initially thought.

This reverts commit c584b8a7ad.

Reported-by: Greg Ungerer <gregungerer@westnet.com.au>
Closes: https://lore.kernel.org/all/b55ac37f-4523-46d0-8e77-3a17d7235ffe@westnet.com.au/
Acked-by: Arnd Bergmann <arnd@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/maps/Kconfig

@@ -277,6 +277,12 @@ config MTD_PCMCIA_ANONYMOUS
 
 	  If unsure, say N.
 
+config MTD_UCLINUX
+	bool "Generic uClinux RAM/ROM filesystem support"
+	depends on (MTD_RAM=y || MTD_ROM=y) && (!MMU || COLDFIRE)
+	help
+	  Map driver to support image based filesystems for uClinux.
+
 config MTD_PLATRAM
 	tristate "Map driver for platform device RAM (mtd-ram)"
 	select MTD_RAM

drivers/mtd/maps/Makefile

@@ -30,6 +30,7 @@ obj-$(CONFIG_MTD_SUN_UFLASH)	+= sun_uflash.o
 obj-$(CONFIG_MTD_SCx200_DOCFLASH)+= scx200_docflash.o
 obj-$(CONFIG_MTD_SOLUTIONENGINE)+= solutionengine.o
 obj-$(CONFIG_MTD_PCI)		+= pci.o
+obj-$(CONFIG_MTD_UCLINUX)	+= uclinux.o
 obj-$(CONFIG_MTD_SCB2_FLASH)	+= scb2_flash.o
 obj-$(CONFIG_MTD_PLATRAM)	+= plat-ram.o
 obj-$(CONFIG_MTD_VMU)		+= vmu-flash.o

drivers/mtd/maps/uclinux.c

@@ -0,0 +1,118 @@
+/****************************************************************************/
+
+/*
+ *	uclinux.c -- generic memory mapped MTD driver for uclinux
+ *
+ *	(C) Copyright 2002, Greg Ungerer (gerg@snapgear.com)
+ *
+ *      License: GPL
+ */
+
+/****************************************************************************/
+
+#include <linux/moduleparam.h>
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/major.h>
+#include <linux/mtd/mtd.h>
+#include <linux/mtd/map.h>
+#include <linux/mtd/partitions.h>
+#include <asm/io.h>
+#include <asm/sections.h>
+
+/****************************************************************************/
+
+#ifdef CONFIG_MTD_ROM
+#define MAP_NAME "rom"
+#else
+#define MAP_NAME "ram"
+#endif
+
+static struct map_info uclinux_ram_map = {
+	.name = MAP_NAME,
+	.size = 0,
+};
+
+static unsigned long physaddr = -1;
+module_param(physaddr, ulong, S_IRUGO);
+
+static struct mtd_info *uclinux_ram_mtdinfo;
+
+/****************************************************************************/
+
+static const struct mtd_partition uclinux_romfs[] = {
+	{ .name = "ROMfs" }
+};
+
+#define	NUM_PARTITIONS	ARRAY_SIZE(uclinux_romfs)
+
+/****************************************************************************/
+
+static int uclinux_point(struct mtd_info *mtd, loff_t from, size_t len,
+	size_t *retlen, void **virt, resource_size_t *phys)
+{
+	struct map_info *map = mtd->priv;
+	*virt = map->virt + from;
+	if (phys)
+		*phys = map->phys + from;
+	*retlen = len;
+	return(0);
+}
+
+/****************************************************************************/
+
+static int __init uclinux_mtd_init(void)
+{
+	struct mtd_info *mtd;
+	struct map_info *mapp;
+
+	mapp = &uclinux_ram_map;
+
+	if (physaddr == -1)
+		mapp->phys = (resource_size_t)__bss_stop;
+	else
+		mapp->phys = physaddr;
+
+	if (!mapp->size)
+		mapp->size = PAGE_ALIGN(ntohl(*((unsigned long *)(mapp->phys + 8))));
+	mapp->bankwidth = 4;
+
+	printk("uclinux[mtd]: probe address=0x%x size=0x%x\n",
+	       	(int) mapp->phys, (int) mapp->size);
+
+	/*
+	 * The filesystem is guaranteed to be in direct mapped memory. It is
+	 * directly following the kernels own bss region. Following the same
+	 * mechanism used by architectures setting up traditional initrds we
+	 * use phys_to_virt to get the virtual address of its start.
+	 */
+	mapp->virt = phys_to_virt(mapp->phys);
+
+	if (mapp->virt == 0) {
+		printk("uclinux[mtd]: no virtual mapping?\n");
+		return(-EIO);
+	}
+
+	simple_map_init(mapp);
+
+	mtd = do_map_probe("map_" MAP_NAME, mapp);
+	if (!mtd) {
+		printk("uclinux[mtd]: failed to find a mapping?\n");
+		return(-ENXIO);
+	}
+
+	mtd->owner = THIS_MODULE;
+	mtd->_point = uclinux_point;
+	mtd->priv = mapp;
+
+	uclinux_ram_mtdinfo = mtd;
+	mtd_device_register(mtd, uclinux_romfs, NUM_PARTITIONS);
+
+	return(0);
+}
+device_initcall(uclinux_mtd_init);
+
+/****************************************************************************/