[PATCH v7 0/4] mtd: spi-nor: add support for is25wp256 spi-nor flash

[Sagar Shrikant Kadam]

The patch series adds support for 32MiB spi-nor is25wp256 present on HiFive
Unleashed A00 board. The flash device gets BFPT_DWORD1_ADDRESS_BYTES_3_ONLY
from BFPT table for address width, whereas the flash can support 4 byte
address width, so the address width is configured by using the post bfpt
fixup hook as done for is25lp256 device in
commit cf580a924005 ("mtd: spi-nor: fix nor->addr_width when its value
configured from SFDP does not match the actual width") queued in
spi-nor/next branch [1].

Patches 1 and 3 are based on original work done by Wesley Terpstra and/or
Palmer Dabbelt:
https://github.com/riscv/riscv-linux/commit/c94e267766d62bc9a669611c3d0c8ed5ea26569b

Erase/Read/Write operations are verified on HiFive Unleashed board using  mtd and
flash utils (v1.5.2):
1. mtd_debug  	: Options available are : erase/read/write.
2. flashcp	: Single utility that erases flash, writes a file to flash and verifies the data back.
3. flash_unlock : Unlock flash memory blocks. Arguments: are offset and number of blocks.
3. flash_lock   : Lock flash memory blocks. Arguments: are offset and number of blocks. 

The Unlock scheme clears the protection bits of all blocks in the Status register.

Lock scheme:
A basic implementation based on the stm_lock scheme and is validated for a different
number of blocks passed to flash_lock. ISSI devices have top/bottom area selection
in function register which is OTP memory. so we are not updating the OTP section
of function register.

The changes along are available under branch v5.2-rc1-mtd-spi-nor/next at:
https://github.com/sagsifive/riscv-linux-hifive 
 
[1] https://git.kernel.org/pub/scm/linux/kernel/git/mtd/linux.git/log/?h=spi-nor/next

Revision history:
V6<->V7:
-Incorporated review comments from Vignesh.
-Used post bfpt fixup hook as suggested by Vignesh.
-Introduce SPI_NOR_HAS_BP3 to identify whether the flash has 4th bit protect bit.
-Prefix generic flash access functions with spi_nor_xxxx.

V5<->V6:
-Incorporated review comments from Vignesh.
-Set addr width based on device size and if SPI_NOR_4B_OPCODES is set.
-Added 4th block protect identifier (SPI_NOR_HAS_BP3) to flash_info structure 
-Changed flash_info: flag from u16 to u32 to accommodate SPI_NOR_HAS_BP3
-Prefix newly added function with spi_nor_xxx.
-Dropped write_fr function, as updating OTP bit's present in function register doesn't seem to be a good idea.
-Set lock/unlock schemes based on whether the ISSI device has locking support and  BP3 bit present.

V4<->V5:
-Rebased to linux version v5.2-rc1.
-Updated heading of this cover letter with sub-system, instead of just plain "add support for is25wp256..."

V3<->V4:
-Extracted comman code and renamed few stm functions so that it can be reused for issi lock implementation.
-Added function's to read and write FR register, for selecting Top/Bottom area.

V2<->V3:
-Rebased patch to mainline v5.1 from earlier v5.1-rc5.
-Updated commit messages, and cover letter with reference to git URL and author information.
-Deferred flash_lock mechanism and can go as separate patch. 

V1<-> V2:
-Incorporated changes suggested by reviewers regarding patch/cover letter versioning, references of patch.
-Updated cover letter with description for flash operations verified with these changes.
-Add support for unlocking is25xxxxxx device.
-Add support for locking is25xxxxxx device.

v1:
-Add support for is25wp256 device.

Sagar Shrikant Kadam (4):
  mtd: spi-nor: add support for is25wp256
  mtd: spi-nor: fix nor->addr_width for is25wp256
  mtd: spi-nor: add support to unlock the flash device
  mtd: spi-nor: add locking support for is25wp256 device

 drivers/mtd/spi-nor/spi-nor.c | 343 +++++++++++++++++++++++++++++++++++-------
 include/linux/mtd/spi-nor.h   |   8 +
 2 files changed, 300 insertions(+), 51 deletions(-)

-- 
1.9.1