mtd: spi-nor: fix Spansion regressions (aliased with Winbond)

Spansion and Winbond have occasionally used the same manufacturer ID,
and they don't support the same features. Particularly, writing SR=0
seems to break read access for Spansion's s25fl064k. Unfortunately, we
don't currently have a way to differentiate these Spansion and Winbond
parts, so rather than regressing support for these Spansion flash, let's
drop the new Winbond lock/unlock support for now. We can try to address
Winbond support during the next release cycle.

Original discussion:

http://patchwork.ozlabs.org/patch/549173/
http://patchwork.ozlabs.org/patch/553683/

Fixes: 357ca38d ("mtd: spi-nor: support lock/unlock/is_locked for Winbond")
Fixes: c6fc2171 ("mtd: spi-nor: disable protection for Winbond flash at startup")
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Reported-by: Felix Fietkau <nbd@openwrt.org>
Cc: Felix Fietkau <nbd@openwrt.org>

drivers/mtd/spi-nor/spi-nor.c

@@ -1200,8 +1200,7 @@ int spi_nor_scan(struct spi_nor *nor, const char *name, enum read_mode mode)
 
 	if (JEDEC_MFR(info) == SNOR_MFR_ATMEL ||
 	    JEDEC_MFR(info) == SNOR_MFR_INTEL ||
-	    JEDEC_MFR(info) == SNOR_MFR_SST ||
-	    JEDEC_MFR(info) == SNOR_MFR_WINBOND) {
+	    JEDEC_MFR(info) == SNOR_MFR_SST) {
 		write_enable(nor);
 		write_sr(nor, 0);
 	}
@@ -1217,8 +1216,7 @@ int spi_nor_scan(struct spi_nor *nor, const char *name, enum read_mode mode)
 	mtd->_read = spi_nor_read;
 
 	/* NOR protection support for STmicro/Micron chips and similar */
-	if (JEDEC_MFR(info) == SNOR_MFR_MICRON ||
-	    JEDEC_MFR(info) == SNOR_MFR_WINBOND) {
+	if (JEDEC_MFR(info) == SNOR_MFR_MICRON) {
 		nor->flash_lock = stm_lock;
 		nor->flash_unlock = stm_unlock;
 		nor->flash_is_locked = stm_is_locked;

include/linux/mtd/spi-nor.h

@@ -25,7 +25,7 @@
 #define SNOR_MFR_MACRONIX	CFI_MFR_MACRONIX
 #define SNOR_MFR_SPANSION	CFI_MFR_AMD
 #define SNOR_MFR_SST		CFI_MFR_SST
-#define SNOR_MFR_WINBOND	0xef
+#define SNOR_MFR_WINBOND	0xef /* Also used by some Spansion */
 
 /*
  * Note on opcode nomenclature: some opcodes have a format like