[FS#3914] Failsafe button is inverted under TP-Link TL-WR842N/ND v2

[OpenWrt Bugs]

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A new Flyspray task has been opened.  Details are below. 

User who did this - George (George-TL) 

Attached to Project - OpenWrt/LEDE Project
Summary - Failsafe button is inverted under TP-Link TL-WR842N/ND v2
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - openwrt-19.07
Due in Version - Undecided
Due Date - Undecided
Details - My 2 routers (TL-WR842v1, TL-WR842v2) were modded to have 64MB of RAM.
I also have TL-WR842v3 for reference.

This is great time to move from 17.01 to 19.07 ("refs/heads/openwrt-19.07" branch).
My build configuration is very simple: stock .config + Luci.
Config files are differ only on this line:
  CONFIG_TARGET_ath79_generic_DEVICE_tplink_tl-wr842n-v1=y
  CONFIG_TARGET_ath79_generic_DEVICE_tplink_tl-wr842n-v2=y
  CONFIG_TARGET_ath79_generic_DEVICE_tplink_tl-wr842n-v3=y
Builds were made on ec76c365c1d60bf6a4f69b1ab3ce132f97f34dbb checkout (2021-06-14 - Koen Vandeputte - gitignore: add .ccache folder).

Boxes with hardware revisions v1 and v3 are working just fine.
But v2 almost always boots into failsafe mode :(
If I hold "wifi on/off" button v2 boots normal.
My wild guess: GPIO configuration is broken.

After 'git bisect' session I've found that following commit makes big difference:
2021-02-26 - Koen Vandeputte - kernel: bump 4.14 to 4.14.222 (b4a4d04b919b4a18a03e52a9e6bc18ddd924f554)
I'm not skilled enough to dig into kernel bisecting territory.

Before above commit router almost always boots normal.
After it router almost always boots into failsafe mode. But if I reboot it using reboot at SSH command it will boot just fine. So, power cycle => failsafe, reboot command => boots normal.

Looks like some sort of hardware initialization is made "too late" in boot process and querying GPIO state gives wrong readings.
That explains proper behavior after soft reboot.

More information can be found at the following URL:
https://bugs.openwrt.org/index.php?do=details&task_id=3914

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