mtd: spi-nor: Reorder the preparation vs. locking steps

The ->prepare()/->unprepare() hooks are now legacy, we no longer accept
new drivers supporting them. The only remaining controllers using them
acquires a per-chip mutex, which should not interfere with the rest of
the operation done in the core. As a result, we should be safe to
reorganize these helpers to first perform the preparation, before
acquiring the core locks. This is necessary in order to be able to
improve the locking mechanism in the core (coming next). No side effects
are expected.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20230328154105.448540-4-miquel.raynal@bootlin.com
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>

mtd: spi-nor: s/addr_width/addr_nbytes

Address width was an unfortunate name, as it means the number of IO lines
used for the address, whereas in the code it is used as the number of
address bytes. s/addr_width/addr_nbytes throughout the entire SPI NOR
framework.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Michael Walle <michael@walle.cc>
Acked-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20220725092505.446315-2-tudor.ambarus@microchip.com

mtd: spi-nor: Introduce spi_nor_set_mtd_info()

Used to init all the mtd_info fields. Move the mtd_info init
the last thing in the spi_nor_scan(), so that we avoid superfluous
initialization of the mtd_info fields in case of errors.

While here use common naming scheme for functions that are setting
mtd_info fields:
s/spi_nor_register_locking_ops/spi_nor_set_mtd_locking_ops
s/spi_nor_otp_init/spi_nor_set_mtd_otp_ops
The functions names are self explanatory, get rid of the comment
for the OTP function.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Michael Walle <michael@walle.cc>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20211207140254.87681-4-tudor.ambarus@microchip.com

mtd: spi-nor: otp: implement erase for Winbond and similar flashes

Winbond flashes with OTP support provide a command to erase the OTP
data. This might come in handy during development.

This was tested with a Winbond W25Q32JW on a LS1028A SoC with the
NXP FSPI controller.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>

mtd: spi-nor: otp: return -EROFS if region is read-only

SPI NOR flashes will just ignore program commands if the OTP region is
locked. Thus, a user might not notice that the intended write didn't end
up in the flash. Return -EROFS to the user in this case. From what I can
tell, chips/cfi_cmdset_0001.c also return this error code.

One could optimize spi_nor_mtd_otp_range_is_locked() to read the status
register only once and not for every OTP region, but for that we would
need some more invasive changes. Given that this is
one-time-programmable memory and the normal access mode is reading, we
just live with the small overhead.

By moving the code around a bit, we can just check the length before
calling spi_nor_mtd_otp_range_is_locked() and avoid an underflow there
if a len is 0. This way we don't need to take the lock either. We also
skip the "*retlen = 0" assignment, mtdcore already takes care of that
for us.

Fixes: 069089acf88b ("mtd: spi-nor: add OTP support")
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>

mtd: spi-nor: otp: use more consistent wording

Use the wording as used in the datasheet to describe the access methods
of the security registers (aka OTP storage). This will also match the
function names.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>

mtd: spi-nor: otp: fix access to security registers in 4 byte mode

The security registers either take a 3 byte or a 4 byte address offset,
depending on the address mode of the flash. Thus just leave the
nor->addr_width as is.

Fixes: cad3193fe9d1 ("mtd: spi-nor: implement OTP support for Winbond and similar flashes")
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Acked-by: Pratyush Yadav <p.yadav@ti.com>

mtd: spi-nor: otp: fix kerneldoc typos

Use the correct argument names in the kerneldoc.

Fixes: cad3193fe9d1 ("mtd: spi-nor: implement OTP support for Winbond and similar flashes")
Reported-by: Pratyush Yadav <p.yadav@ti.com>
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Reviewed-by: Pratyush Yadav <p.yadav@ti.com>

mtd: core: Constify buf in mtd_write_user_prot_reg()

The write buffer comes from user and should be const.
Constify write buffer in mtd core and across all _write_user_prot_reg()
users. cfi_cmdset_{0001, 0002} and onenand_base will pay the cost of an
explicit cast to discard the const qualifier since the beginning, since
they are using an otp_op_t function prototype that is used for both reads
and writes. mtd_dataflash and SPI NOR will benefit of the const buffer
because they are using different paths for writes and reads.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20210403060931.7119-1-tudor.ambarus@microchip.com

mtd: spi-nor: implement OTP support for Winbond and similar flashes

Use the new OTP ops to implement OTP access on Winbond flashes. Most
Winbond flashes provides up to four different OTP regions ("Security
Registers").

Winbond devices use a special opcode to read and write to the OTP
regions, just like the RDSFDP opcode. In fact, it seems that the
(undocumented) first OTP area of the newer flashes is the actual SFDP
table.

On a side note, Winbond devices also allow erasing the OTP regions as
long as the area isn't locked down.

Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20210321235140.8308-3-michael@walle.cc

mtd: spi-nor: add OTP support

SPI flashes sometimes have a special OTP area, which can (and is) used to
store immutable properties like board serial number or vendor assigned
network hardware addresses.

The MTD subsystem already supports accessing such areas and some (non
SPI NOR) flashes already implement support for it. It differentiates
between user and factory areas. User areas can be written by the user and
factory ones are pre-programmed and locked down by the vendor, usually
containing an "electrical serial number". This patch will only add support
for the user areas.

Lay the foundation and implement the MTD callbacks for the SPI NOR and add
necessary parameters to the flash_info structure. If a flash supports OTP
it can be added by the convenience macro OTP_INFO(). Sometimes there are
individual regions, which might have individual offsets. Therefore, it is
possible to specify the starting address of the first regions as well as
the distance between two regions (e.g. Winbond devices uses this method).

Additionally, the regions might be locked down. Once locked, no further
write access is possible.

For SPI NOR flashes the OTP area is accessed like the normal memory, e.g.
by offset addressing; except that you either have to use special read/write
commands (Winbond) or you have to enter (and exit) a specific OTP mode
(Macronix, Micron).

Thus we introduce four operations to which the MTD callbacks will be
mapped: .read(), .write(), .lock() and .is_locked(). The read and the write
ops will be given an address offset to operate on while the locking ops use
regions because locking always affects a whole region. It is up to the
flash driver to implement these ops.

Signed-off-by: Michael Walle <michael@walle.cc>
[ta: use div64_u64(), IS_ALIGNED, params->otp.org. unsigned int region,
drop comment, add rlen local variable in spi_nor_mtd_otp_lock()]
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20210321235140.8308-2-michael@walle.cc