mtd: add a flags for partitions which should just leave smth. after them

Add support for MTDPART_OFS_RETAIN: such partitions start at the current
offset, take as much space as possible, but rain part->size bytes after
the end of the partitions for other parts. Primarily this is intended
for ts72xx arm platforms cleanup.

Artem: tweaked the patch a bit

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

drivers/mtd/mtdpart.c

@@ -479,6 +479,19 @@ static struct mtd_part *allocate_partition(struct mtd_info *master,
 			       (unsigned long long)cur_offset, (unsigned long long)slave->offset);
 		}
 	}
+	if (slave->offset == MTDPART_OFS_RETAIN) {
+		slave->offset = cur_offset;
+		if (master->size - slave->offset >= slave->mtd.size) {
+			slave->mtd.size = master->size - slave->offset
+							- slave->mtd.size;
+		} else {
+			printk(KERN_ERR "mtd partition \"%s\" doesn't have enough space: %#llx < %#llx, disabled\n",
+				part->name, master->size - slave->offset,
+				slave->mtd.size);
+			/* register to preserve ordering */
+			goto out_register;
+		}
+	}
 	if (slave->mtd.size == MTDPART_SIZ_FULL)
 		slave->mtd.size = master->size - slave->offset;
 

include/linux/mtd/partitions.h

@@ -24,7 +24,9 @@
  * 	will extend to the end of the master MTD device.
  * offset: absolute starting position within the master MTD device; if
  * 	defined as MTDPART_OFS_APPEND, the partition will start where the
- * 	previous one ended; if MTDPART_OFS_NXTBLK, at the next erase block.
+ *	previous one ended; if MTDPART_OFS_NXTBLK, at the next erase block;
+ *	if MTDPART_OFS_RETAIN, consume as much as possible, leaving size
+ *	after the end of partition.
  * mask_flags: contains flags that have to be masked (removed) from the
  * 	master MTD flag set for the corresponding MTD partition.
  * 	For example, to force a read-only partition, simply adding
@@ -42,6 +44,7 @@ struct mtd_partition {
 	struct nand_ecclayout *ecclayout;	/* out of band layout for this partition (NAND only) */
 };
 
+#define MTDPART_OFS_RETAIN	(-3)
 #define MTDPART_OFS_NXTBLK	(-2)
 #define MTDPART_OFS_APPEND	(-1)
 #define MTDPART_SIZ_FULL	(0)