mtd: spi-nor: core: Track flash's internal address mode

We need to track the flash's internal address mode as there are flashes
that can operate with 4B opcodes but unfortunately do not have a 4B opcode
correspondent for all the 3B opcodes. Such an example is the Infineon
Semper chips which provide 4B opcodes for read/program/erase but do not
provide 4B opcodes for Read/Write Any Register. These registers are
indexed by address and require the internal address mode of the flash
before Read/Write Any Register opcodes are issued.
4B opcodes are preferred over changing the flash's address mode to 4byte,
as set_4byte_addr_mode could be done in a non-volatile way and could break
the boot sequence. Thus we need to track the flash's internal address mode
so that we can use 4B opcodes together with opcodes that don't have a 4B
opcode correspondent. Track flash's internal address mode.

addr_mode_nbytes is discovered when parsing BFPT. For the
BFPT_DWORD1_ADDRESS_BYTES_3_OR_4 case, one could introduce a method that
queries the flash's internal address mode at run-time (works for Winbond).
If a run-time querying can not be accomplished or if SFDP is not defined
at all, but the address mode is volatile and resets to a default known
value at boot, one can change the default addr_mode_nbytes value of 3 by
introducing a flash_info flag. If the address mode can not be queried,
discovered and it is configured via a non-volatile register, we may
introduce a dt property, but it will harm the generic approach of the
jedec,spi-nor compatible. All this complexity is not needed now, so let it
for future development.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Reviewed-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20220725092505.446315-6-tudor.ambarus@microchip.com

Author: ambarus

drivers/mtd/spi-nor/core.h

@@ -341,6 +341,10 @@ struct spi_nor_otp {
  *			ECC unit size for ECC-ed flashes.
  * @page_size:		the page size of the SPI NOR flash memory.
  * @addr_nbytes:	number of address bytes to send.
+ * @addr_mode_nbytes:	number of address bytes of current address mode. Useful
+ *			when the flash operates with 4B opcodes but needs the
+ *			internal address mode for opcodes that don't have a 4B
+ *			opcode correspondent.
  * @rdsr_dummy:		dummy cycles needed for Read Status Register command
  *			in octal DTR mode.
  * @rdsr_addr_nbytes:	dummy address bytes needed for Read Status Register
@@ -374,6 +378,7 @@ struct spi_nor_flash_parameter {
 	u32				writesize;
 	u32				page_size;
 	u8				addr_nbytes;
+	u8				addr_mode_nbytes;
 	u8				rdsr_dummy;
 	u8				rdsr_addr_nbytes;
 

drivers/mtd/spi-nor/sfdp.c

@@ -463,10 +463,12 @@ static int spi_nor_parse_bfpt(struct spi_nor *nor,
 	case BFPT_DWORD1_ADDRESS_BYTES_3_ONLY:
 	case BFPT_DWORD1_ADDRESS_BYTES_3_OR_4:
 		params->addr_nbytes = 3;
+		params->addr_mode_nbytes = 3;
 		break;
 
 	case BFPT_DWORD1_ADDRESS_BYTES_4_ONLY:
 		params->addr_nbytes = 4;
+		params->addr_mode_nbytes = 4;
 		break;
 
 	default:
@@ -653,7 +655,7 @@ static u8 spi_nor_smpt_addr_nbytes(const struct spi_nor *nor, const u32 settings
 		return 4;
 	case SMPT_CMD_ADDRESS_LEN_USE_CURRENT:
 	default:
-		return nor->params->addr_nbytes;
+		return nor->params->addr_mode_nbytes;
 	}
 }