push-pull stalls (QCA 9888)

[Guilherme Weidle]

Hi,

I'm suffering from a bug where in AP mode, the TX queue stalls.

If I connect 5 stations and force some traffic (bandwidth test for
instance), the AP's TX queue seems to stall (no data frames are
getting out).

I can reply this issue by using another device (ath9k) with 5 virtual
interfaces (stations) connected to my AP (ath10k). Then, I start iperf
server on that device and start one iperf client (from AP) per
associated station. And just like that, AP stops sending data frames
and I no longer be able to ping any connected station.

If I do the same test, but with 4 stations instead of 5, it works just fine.

As far as I could see, it is related to PUSH-PULL mode. As soon as the
WLAN firmware switches to this mode, the issue happens.

Just as a test, I change the ath10k_mac_tx_can_push() to always return
true and the issue goes away.

Does anyone also came across this issue or have any idea how to solve it?

PS: This product is using kernel 4.4.60 and backports 4.19.137-1. I
also updated to backports 20210222_001 and the problem still there.

Regards,

Guilherme Weidle