View source for Updating nand flash driver from linux kernel 4.14 to 4.19

==About==
Below are the changes had to be made to update our nand flash driver code from kernel 4.14 to 4.19.
The kernel versions mentioned are the rebases from the mainline kernel in linux-xlnx repo with xilinx's code:
 [https://github.com/Xilinx/linux-xlnx/tree/xlnx_rebase_v4.14 xlnx_rebase_v4.14]
 [https://github.com/Xilinx/linux-xlnx/tree/xlnx_rebase_v4.19 xlnx_rebase_v4.19]  

==NAND FLASH chip==
Micron MT29F8G08ADBDAH4:
* ON-DIE ECC feature supported - they call it internal ECC in the datasheet:
 Internal ECC enables 5-bit detection and 4-bit error correction in 512 bytes

==Linux Kernel 4.14 and older==
Until 4.14 (including) our driver code additions worked unchanged. We basically needed a couple of things:
* LOCK/UNLOCK functions (which were removed in 4.14). The code existed in up to 4.13 release - so it was just taken from there.
* Function to work with the chip's (MT29F8G08ADBDAH4) OTP area. The original code was taken from [http://webcache.googleusercontent.com/search?q=cache:-k_EdkxxQCUJ:lists.infradead.org/pipermail/linux-mtd/2013-March/045994.html+&cd=2&hl=en&ct=clnk&gl=us&client=ubuntu here]

==Updating to 4.19==
===Notes===
* A lot has changed since 4.14
** new ''->exec_op'' hook vs old ''->cmdfunc''
** Xilinx tries to keep up with their driver - they might have tested this on [https://lwn.net/Articles/756725/ Micron MT29F2G08ABAEAWP (On-die capable) and AMD/Spansion S34ML01G1]
* OTP function are not supported yet, and need a minor change to make them more universal
 That minor change is to set ops.mode to MTD_OPS_RAW instead of normal. Hooks for normal ops
 can enable/disable ECC features which will reset OTP mode (which is also a feature set)

* Old LOCK/UNLOCK functions from pre 4.14 kernel need to be updated to the new codebase
 Those op_parser patterns. 
 Also UNLOCK command is 2 parts: 0x23 BOUND_LO 0x24 BOUND_HI - so, before 0x24 has to be some sort of a delay or the op should be split into 2.
 Datasheet does not provide any timing info

* Set ''nand-ecc-mode = "on-die";'' in the device tree. 
 In 4.14 it used to be detected as "on-die", but not anymore.
* Add NAND_NO_SUBPAGE_WRITE to chip->options for MT29F8G08ADBDAH4
 Otherwise driver goes for subpage program support. '''Need to test this.'''

===Driver code===
See the code here:
* [https://git.elphel.com/Elphel/linux-elphel/blob/warrior/src/arch/arm/boot/dts/elphel393-zynq-base.dtsi#L299 device tree]
 Those ''arm,nand-cycle-t0-6'' are obsolete and can be removed from DT.
* [https://git.elphel.com/Elphel/linux-elphel/tree/d4f217cf68d8c3c9a84f680dd014b1a0de0571c8/src/drivers/mtd/nand/raw driver code]
 Didn't make a patch - the changes are for a specific MT29F8G08ADBDAH4. Although they might work for other chips as well we have only tested the one we use.