sf: Make 4K sector support configurable

Make the support for 4K subpage I/O on a SPI NOR flash configurable.
A board which requires the SPI NOR to be accessed in larger 32KiB
or 64KiB pages can disable the 4K subpage support, but by default,
the support for 4K subpage I/O is enabled. The functionality of this
option is the same as CONFIG_MTD_SPI_NOR_USE_4K_SECTORS in Linux.

This is extremely useful in case one uses UBI on a SPI NOR flash.
UBI needs at least 15k EBs and can not work on a flash which uses
4k ones, so disabling the support for 4k subpages lets UBI work on
such flash.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Jagan Teki <jteki@openedev.com>

drivers/mtd/spi/Kconfig

@@ -86,6 +86,21 @@ config SPI_FLASH_WINBOND
 
 endif
 
+config SPI_FLASH_USE_4K_SECTORS
+	bool "Use small 4096 B erase sectors"
+	depends on SPI_FLASH
+	default y
+	help
+	  Many flash memories support erasing small (4096 B) sectors. Depending
+	  on the usage this feature may provide performance gain in comparison
+	  to erasing whole blocks (32/64 KiB).
+	  Changing a small part of the flash's contents is usually faster with
+	  small sectors. On the other hand erasing should be faster when using
+	  64 KiB block instead of 16 × 4 KiB sectors.
+
+	  Please note that some tools/drivers/filesystems may not work with
+	  4096 B erase size (e.g. UBIFS requires 15 KiB as a minimum).
+
 config SPI_FLASH_DATAFLASH
 	bool "AT45xxx DataFlash support"
 	depends on SPI_FLASH && DM_SPI_FLASH

drivers/mtd/spi/sf_internal.h

@@ -37,7 +37,11 @@ enum spi_read_cmds {
 
 /* sf param flags */
 enum {
+#ifdef CONFIG_SPI_FLASH_USE_4K_SECTORS
 	SECT_4K		= 1 << 0,
+#else
+	SECT_4K		= 0 << 0,
+#endif
 	SECT_32K	= 1 << 1,
 	E_FSR		= 1 << 2,
 	SST_BP		= 1 << 3,