mtd: cfi_cmdset_0002: do not fail on no extended query table as they are both optional

After looking at AMD's CFI specification [1], both of the extended query
tables are optional. Thus, it looks like relying that at least one of
those tables exist is a bug in cfi_cmdset_0002.

This patch inverts the logic and checks for unlock function pointers before
exiting on error. This approach leaves place to add a call to a fixup
function to try to handle chips compatible with the early AMD specification
from 1995 [2].

[1] http://www.amd.com/us-en/assets/content_type/DownloadableAssets/cfi_r20.pdf
[2] http://noel.feld.cvut.cz/hw/amd/20158a.pdf

Signed-off-by: Guillaume LECERF <glecerf@gmail.com>
Reviewed-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/mtd/chips/cfi_cmdset_0002.c

@@ -357,20 +357,15 @@ struct mtd_info *cfi_cmdset_0002(struct map_info *map, int primary)
 
 	if (cfi->cfi_mode==CFI_MODE_CFI){
 		unsigned char bootloc;
-		/*
-		 * It's a real CFI chip, not one for which the probe
-		 * routine faked a CFI structure. So we read the feature
-		 * table from it.
-		 */
 		__u16 adr = primary?cfi->cfiq->P_ADR:cfi->cfiq->A_ADR;
 		struct cfi_pri_amdstd *extp;
 
 		extp = (struct cfi_pri_amdstd*)cfi_read_pri(map, adr, sizeof(*extp), "Amd/Fujitsu");
-		if (!extp) {
-			kfree(mtd);
-			return NULL;
-		}
-
+		if (extp) {
+			/*
+			 * It's a real CFI chip, not one for which the probe
+			 * routine faked a CFI structure.
+			 */
 			cfi_fixup_major_minor(cfi, extp);
 
 			if (extp->MajorVersion != '1' ||
@@ -416,6 +411,12 @@ struct mtd_info *cfi_cmdset_0002(struct map_info *map, int primary)
 			/* Set the default CFI lock/unlock addresses */
 			cfi->addr_unlock1 = 0x555;
 			cfi->addr_unlock2 = 0x2aa;
+		}
+
+		if (!cfi->addr_unlock1 || !cfi->addr_unlock2) {
+			kfree(mtd);
+			return NULL;
+		}
 
 	} /* CFI mode */
 	else if (cfi->cfi_mode == CFI_MODE_JEDEC) {