On the ath10k-devel ML Michael Kazior stated:

"board-2 is a key-value store of actual board files.
Some devices, notably qca61x4 hw3+ and qca4019 need
distinct board files to be uploaded. Otherwise they
fail in various ways." [0].

Later on Rajkumar Manoharan explained:

"In QCA4019 platform, only radio specific calibration
(pre-cal-data) is stored in flash. Board specific contents
are read from board-2.bin. For each radio appropriate board
data should be loaded. To fetch correct board data from
board-2.bin bundle, pre-cal/radio specific caldata should
be loaded first to get proper board id.

|My understanding until now was that:
|
| * pre-cal data + board-2.bin info == actual calibration data

Correct." [1].
The standard board-2.bin from the ath10k-firmware-qca4019
barely works on the RT-AC58U. Especially 5GHz clients fail
to connect at all and if they do, they have very low
throughput even right next to the router.

Currently, the solution for this problem is to supply a
custom board-2.bin for every device.

To implement this feature, this method makes use of:
Rafał Miłecki's "base-files: add support for overlaying
rootfs content". This comes with a few limitations:
1. Since there can only be one board-2.bin at the right
   location, there can only one board overwrite installed
   at any time. (All packages CONFLICT with each other.
   It's also not possible to "builtin" multiple package.)

2. updating ath10k-firmware-qca4019 will also replace
   the board-2.bin. For this cases the user needs to
   manually reinstall the wifi-board package once the
   ath10k-firmware-qca4019 is updated.

To create the individual board-2.bin: Use the ath10k-bdencoder
utility from the qca-swiss-army-knife repository:
<https://github.com/qca/qca-swiss-army-knife

>
The raw board.bin files have to be extracted from the
vendor's source GPL.tar archieves.

Signed-off-by: Alexis Green <agreen@cococorp.com>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>