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

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: 5390a8df ("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

drivers/mtd/spi-nor/core.c

@@ -1364,14 +1364,15 @@ 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;