mtd: spi-nor: core: Fix erase type discovery for overlaid region

commit 969b276 upstream.

In case of overlaid regions in which their biggest erase size command
overpasses in size the region's size, only the non-overlaid portion of
the sector gets erased. For example, if a Sector Erase command is applied
to a 256-kB range that is overlaid by 4-kB sectors, the overlaid 4-kB
sectors are not affected by the erase.
For overlaid regions, 'region->size' is assigned to 'cmd->size' later in
spi_nor_init_erase_cmd(), so 'erase->size' can be greater than 'len'.

Fixes: 5390a8d ("mtd: spi-nor: add support to non-uniform SFDP SPI NOR flash memories")
Cc: stable@vger.kernel.org
Signed-off-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
[ta: Update commit description, add Fixes tag and Cc to stable]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/fa5d8b944a5cca488ac54ba37c95e775ac2deb34.1601612872.git.Takahiro.Kuwano@infineon.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/mtd/spi-nor/core.c

@@ -1212,14 +1212,15 @@ spi_nor_find_best_erase_type(const struct spi_nor_erase_map *map,
 
 		erase = &map->erase_type[i];
 
+		/* Alignment is not mandatory for overlaid regions */
+		if (region->offset & SNOR_OVERLAID_REGION &&
+		    region->size <= len)
+			return erase;
+
 		/* Don't erase more than what the user has asked for. */
 		if (erase->size > len)
 			continue;
 
-		/* Alignment is not mandatory for overlaid regions */
-		if (region->offset & SNOR_OVERLAID_REGION)
-			return erase;
-
 		spi_nor_div_by_erase_size(erase, addr, &rem);
 		if (rem)
 			continue;