eeprom: at25: Add DT support for EEPROMs with odd address bits

Certain EEPROMS have a size that is larger than the number of address
bytes would allow, and store the MSB of the address in bit 3 of the
instruction byte.

This can be described in platform data using EE_INSTR_BIT3_IS_ADDR, or
in DT using the obsolete legacy "at25,addr-mode" property.
But currently there exists no non-deprecated way to describe this in DT.

Hence extend the existing "address-width" DT property to allow
specifying 9 address bits, and enable support for that in the driver.

This has been tested with a Microchip 25LC040A.
Signed-off-by: NGeert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/eeprom/at25.txt

@@ -11,7 +11,9 @@ Required properties:
 - spi-max-frequency : max spi frequency to use
 - pagesize : size of the eeprom page
 - size : total eeprom size in bytes
-- address-width : number of address bits (one of 8, 16, or 24)
+- address-width : number of address bits (one of 8, 9, 16, or 24).
+  For 9 bits, the MSB of the address is sent as bit 3 of the instruction
+  byte, before the address byte.
 
 Optional properties:
 - spi-cpha : SPI shifted clock phase, as per spi-bus bindings.

drivers/misc/eeprom/at25.c

@@ -276,6 +276,9 @@ static int at25_fw_to_chip(struct device *dev, struct spi_eeprom *chip)
 			return -ENODEV;
 		}
 		switch (val) {
+		case 9:
+			chip->flags |= EE_INSTR_BIT3_IS_ADDR;
+			/* fall through */
 		case 8:
 			chip->flags |= EE_ADDR1;
 			break;