mtd: map_rom: Support UBI on ROM

UBI needs to know the physical erase block size, even on read-only
devices, since it defines the on-device layout. Use a device-tree
provided value to support previously written UBI on read-only NOR.

UBI also needs a non-zero writebufsize, so we set it to one.

Note: This was implemented because hardware write-protected CFI
      NOR cannot be probed for the physical erase block size.

Signed-off-by: Joe Schultz <jschultz@xes-inc.ccom>
Signed-off-by: Aaron Sierra <asierra@xes-inc.ccom>
[Brian: removed unneeded #ifdef, note 'optional' erase-size property]
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/drivers/mtd/chips/map_rom.c b/drivers/mtd/chips/map_rom.c
index 47a43cf7e5c6..e67f73ab44c9 100644
--- a/drivers/mtd/chips/map_rom.c
+++ b/drivers/mtd/chips/map_rom.c
@@ -11,6 +11,7 @@
 #include <linux/errno.h>
 #include <linux/slab.h>
 #include <linux/init.h>
+#include <linux/of.h>
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/map.h>
 
@@ -28,6 +29,15 @@ static struct mtd_chip_driver maprom_chipdrv = {
         .module = THIS_MODULE
 };
 
+static unsigned int default_erasesize(struct map_info *map)
+{
+        const __be32 *erase_size = NULL;
+
+        erase_size = of_get_property(map->device_node, "erase-size", NULL);
+
+        return !erase_size ? map->size : be32_to_cpu(*erase_size);
+}
+
 static struct mtd_info *map_rom_probe(struct map_info *map)
 {
         struct mtd_info *mtd;
@@ -47,8 +57,9 @@ static struct mtd_info *map_rom_probe(struct map_info *map)
         mtd->_sync = maprom_nop;
         mtd->_erase = maprom_erase;
         mtd->flags = MTD_CAP_ROM;
-        mtd->erasesize = map->size;
+        mtd->erasesize = default_erasesize(map);
         mtd->writesize = 1;
+        mtd->writebufsize = 1;
 
         __module_get(THIS_MODULE);
         return mtd;