[FS#1075] xiaomi mini hardware/power issues

[LEDE Bugs]

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

User who did this - psyborg55 (psyborg55) 

Attached to Project - LEDE Project
Summary - xiaomi mini hardware/power issues
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Low
Priority - Very Low
Reported Version - Trunk
Due in Version - Undecided
Due Date - Undecided
Details - i've noticed recently there is a signal drop on mini when used legacy wifi mode. this mode disables chain1 in mtk driver and use only chain0. i've made detailed test of both firmware with 3 different cards. can somebody else try the same test to conclude if it is power configuration issue or hardware damage?

TX values are card TX which means RSSI from router while RX values are mini's txpower levels received by cards.

AR9271 is AWUS036NHA with 10dB comfast antenna
RT5370 is EDUP 150N mini usb adapter
AR9462 is minipci card
NC means card did not detect beacons in this mode

TX/RX path configuration was changed within eeprom offset 0x34

test results:

MTK			2T1R		OpenWrt

G	N20	N40			G	N20	N40

-25	-25	-25	AR9271 TX	-47	-47	-47
-61	-48	-48	AR9271 RX	-52	-52	-52

NC	-25	-25	RT5370 TX	-50	-50	-50
NC	-29	-29	RT5370 RX	-33	-33	-37

-25	-25	-25	AR9462 TX	-41	-45	-45
-40	-25	-25	AR9462 RX	-35	-35	-35

MTK			1T2R		OpenWrt

G	N20	N40			G	N20	N40

-78	-78	-78	AR9271 TX	-47	-47	-47
-70	-70	-70	AR9271 RX	-75	-75	-75

-79	-79	-79	RT5370 TX	-50	-50	-50
-59	-59	-59	RT5370 RX	-59	-59	-59

-78	-78	-78	AR9462 TX	-43	-45	-45
-45	-45	-45	AR9462 RX	-50	-50	-50

MTK			1T1R		OpenWrt

G	N20	N40			G	N20	N40

-25	-25	-25	AR9271 TX	-47	-47	-47
-70	-70	-70	AR9271 RX	-75	-75	-75

-25	-25	-25	RT5370 TX	-50	-50	-50
-59	-59	-59	RT5370 RX	-59	-59	-59

-23	-23	-23	AR9462 TX	-43	-45	-45
-45	-45	-45	AR9462 RX	-50	-50	-50

MTK			2T2R		OpenWrt

G	N20	N40			G	N20	N40

-46	-46	-46	AR9271 TX	-37	-37	-37
-70	-48	-48	AR9271 RX	-52	-52	-52

-44	-44	-47	RT5370 TX	-33	-33	-39
-59	-29	-29	RT5370 RX	-35	-33	-37

-40	-45	-47	AR9462 TX	-35	-37	-39
-45	-25	-25	AR9462 RX	-35	-35	-35

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=1075