Frames acknowledged and silently discarded in firmware

[Javier Cardona]

Hi,

We have observed a problem where, under certain conditions, the ath10k firmware will acknowledge frames but not send them up to the driver.  
Frames are sent by a mesh access point (MAP1) to a second mesh AP (MAP2) at MCS 9/NSS-3, which at that distance is probably marginal.  Since frames get acknlowledged by MAP2, MAP1 will not try a lower rate.  But the driver at MAP2 does not receive the frames.

We have captures of this exchange for both the unsuccessful as well as the successful case, which happens when we move MAP2 closer to MAP1.   They can be found here:
https://www.dropbox.com/sh/0or86c8vxotygdc/AABI7RmQ2nztcOBF3UDXbPUma

In both scenarios, the frames from MAP1 to MAP2 are acknowledged, as observed in sniffer captures.

In the successful scenario, the driver logs show the frames being received by the driver.  Sequence numbers in the debug logs match those in the sniffer captures.

root at nbg-3ed9da:~# journalctl -kf | grep "peer 60:31:97:3e:82:e6" | grep ucast | grep 'len 374'
Feb 05 05:43:31 nbg-3ed9da kernel: ath10k_pci 0000:01:00.0: rx skb d734f6c0 len 374 peer 60:31:97:3e:82:e6 tid 0 (BE) ucast sn 1027 vht sgi rate_idx 9 vht_nss 3 freq 5825 band 1 flag 0x600800 fcs-err 0 mic-err 0 amsdu-more 0
Feb 05 05:43:42 nbg-3ed9da kernel: ath10k_pci 0000:01:00.0: rx skb d6aaa480 len 374 peer 60:31:97:3e:82:e6 tid 0 (BE) ucast sn 1031 vht sgi rate_idx 9 vht_nss 3 freq 5825 band 1 flag 0x600800 fcs-err 0 mic-err 0 amsdu-more 0
Feb 05 05:43:53 nbg-3ed9da kernel: ath10k_pci 0000:01:00.0: rx skb d53a8d80 len 374 peer 60:31:97:3e:82:e6 tid 0 (BE) ucast sn 1037 vht sgi rate_idx 9 vht_nss 3 freq 5825 band 1 flag 0x600800 fcs-err 0 mic-err 0 amsdu-more 0

In the failure scenario, the driver logs show no frames, even if the capture shows that the frames are acknowledged.

root at nbg-3ed9da:~# journalctl -kf | grep "peer 60:31:97:3e:82:e6" | grep ucast | grep 'len 374'
<nothing here>

If we force MAP1 to use a single stream, the frames are received successfully.

  # iw mesh0 set bitrates legacy-5 ht-mcs-5 vht-mcs-5 1:0-9

It seems as if the firmware is acknowledging but silently discarding frames… is that possible?
Can anyone provide some pointers on how to troubleshoot this?  

We are using this firmware: https://github.com/kvalo/ath10k-firmware/blob/master/QCA9984/hw1.0/3.4/firmware-5.bin_10.4-3.4-00104 and kernel 4.9.31 with a few cherry-picked patches from the ath10k branch.
The hardware is QCA994.

Best,

Javier