Macronix Flash-Chip Block Protection Clearing 5.10er

[Nick]

The flash-chip mx25l6405d that is contained in the Ubiquity Nanostation 
M5 (XM) is not able to write to the flash with kernel 5.10. Probably, 
caused by invalid block protection clearing. For example the logread 
contains a lot of those messages:

     jffs2: Newly-erased block contained word 0x19852003 at offset 
0x00250000

I added a patch with the help of blocktrron for the 5.4er kernel [0]. 
This patch is not applied in the 5.10er since a lot of rewrites happened 
upstream. However, the underlying issue is the missing 4th block 
protection bit that was not cleared. In upstream Linux you typically set 
SPI_NOR_HAS_LOCK | SPI_NOR_4BIT_B for that kind of flash chips in 
drivers/mtd/spi-nor/macronix.c [1]. I added this for the mx25l6405d, but 
it did not help. I also tried to backport the ("mtd: spi-nor: keep lock 
bits if they are non-volatile") fix and setting 
"CONFIG_MTD_SPI_NOR_SWP_DISABLE", but it also did not help. Did I miss 
something?

[0] - 
https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=c9e9b8c342d918cedfc4d2e1c2f7fd1fcaf0b56b
[1] - 
https://github.com/torvalds/linux/commit/7ea40b54e83baed17d85567cfae56175def39a55#diff-f749d5111926f3afbd8d869c577cb314fb690186ba42a2538a87e5ea7725929e
[2] - 
https://gist.github.com/PolynomialDivision/0c420c6bfcfd681cffa7aac9f346d262
[3] - 
https://github.com/PolynomialDivision/openwrt/blob/984f1c84e8d087a9fa0117d5502b8e19a2a35b98/target/linux/generic/backport-5.10/409-v5.11-mtd-spi-nor-keep-lock-bits-if-they-are-non-volatile.patch