NAND: Scan bad blocks lazily.

Rather than scanning on boot, scan upon the first attempt to check the
badness of a block.  This speeds up boot when not using NAND, and reduces
the likelihood of needing to reflash via JTAG if NAND becomes
nonfunctional.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>

drivers/mtd/nand/nand_base.c

@@ -457,6 +457,11 @@ static int nand_block_checkbad(struct mtd_info *mtd, loff_t ofs, int getchip,
 {
 	struct nand_chip *chip = mtd->priv;
 
+	if (!(chip->options & NAND_BBT_SCANNED)) {
+		chip->scan_bbt(mtd);
+		chip->options |= NAND_BBT_SCANNED;
+	}
+
 	if (!chip->bbt)
 		return chip->block_bad(mtd, ofs, getchip);
 
@@ -2721,10 +2726,9 @@ int nand_scan_tail(struct mtd_info *mtd)
 
 	/* Check, if we should skip the bad block table scan */
 	if (chip->options & NAND_SKIP_BBTSCAN)
-		return 0;
+		chip->options |= NAND_BBT_SCANNED;
 
-	/* Build bad block table */
-	return chip->scan_bbt(mtd);
+	return 0;
 }
 
 /* module_text_address() isn't exported, and it's mostly a pointless

include/linux/mtd/nand.h

@@ -204,6 +204,8 @@ typedef enum {
    (e.g. because it needs them DMA-coherent */
 #define NAND_OWN_BUFFERS	0x00040000
 /* Options set by nand scan */
+/* bbt has already been read */
+#define NAND_BBT_SCANNED	0x40000000
 /* Nand scan has allocated controller struct */
 #define NAND_CONTROLLER_ALLOC	0x80000000