ramips: enable flash variable erasure and fix potential lost configuration issues after upgrade

[DragonBluep]

In the kernel 5.15, the default flash sector erase size of the mt7620 sub-target has been switched to 64k. This may cause configuration loss after upgrading the system. This PR solves the potential issue and enables variable size erasure for all sub-target. The last commit is a small cleanup.

Closes: #8715

[Leo-PL]

Yes, please. Finally reasonable flash performance for MF283+. Thank you!
Will test and report in a few days.

[DragonBluep]

rootfs_data partition will automatically align to 64k regardless of the size of the firmware partition, so we do not need to change the partition table of any device.

root@OpenWrt:~# cat /proc/mtd
dev:    size   erasesize  name
mtd0: 00030000 00010000 "u-boot"
mtd1: 00010000 00010000 "u-boot-env"
mtd2: 00010000 00010000 "factory"
mtd3: 007ad000 00010000 "firmware"
mtd4: 00240000 00010000 "kernel"
mtd5: 0056d000 00010000 "rootfs"
mtd6: 001d0000 00010000 "rootfs_data"
mtd7: 00003000 00010000 "test"

[    1.131202] Creating 5 MTD partitions on "spi0.0":
[    1.183959] 0x000000000000-0x000000030000 : "u-boot"
[    1.242691] 0x000000030000-0x000000040000 : "u-boot-env"
[    1.302620] 0x000000040000-0x000000050000 : "factory"
[    1.361723] 0x000000050000-0x0000007fd000 : "firmware"
[    1.419896] 2 uimage-fw partitions found on MTD device firmware
[    1.485103] Creating 2 MTD partitions on "firmware":
[    1.539711] 0x000000000000-0x000000240000 : "kernel"
[    1.597606] 0x000000240000-0x0000007ad000 : "rootfs"
[    1.653638] mtd: setting mtd5 (rootfs) as root device
[    1.710363] 1 squashfs-split partitions found on MTD device rootfs
[    1.778468] 0x0000005d0000-0x0000007a0000 : "rootfs_data"
[    1.840318] 0x0000007fd000-0x000000800000 : "test"

[peterwillcn]

What is the purpose of the mtd7 test partition and should it not be retained？

[DragonBluep]

What is the purpose of the mtd7 test partition and should it not be retained？

It's just a placeholder that I use to make firmware partition size not aligned to 64k. Just an experiment. I use it to test whether the read and write ability of firmware partition will be affected.

As long as the start address of the partition is aligned to 64k, it is readable and writable. If the start address of the partition is not aligned to 64k, it will be read only. Fortunately, the firmware partition and u-boot-env partition start addresses of all devices are aligned to 64k.

[ptpt52]

mark.

[DragonBluep]

@hauke Sorry I made a mistake here. I didn't notice this error because my local build and ci automatically excluded this device. However, it will surely break the buildbot build.
ref: https://buildbot.staging.openwrt.org/images/#/builders/12/builds/4
I have sent a fix patch to the mailing list and cc to you.

BTW, I suggest marking the rt288x sub-target as source only. Because the only supported device Belkin F5D8235 has only 32MiB RAM, I don't think it can run the 5.15 kernel.