Frames acknowledged and silently discarded in firmware

[Thomas Pedersen]

Javier,

On Tue, Mar 13, 2018 at 4:42 PM, Javier Cardona <jcardona at fb.com> wrote:
> Hi,
>
> We have resolved this issue.  I'm sharing the details in case that might help others.
>
> The description of the problem was accurate EXCEPT that the acks that we observed on the sniffer were not being sent by the failed station (MAP2, in the context of my original e-mail) but by a third station MAP3.  Those Acks were sent by MAP3 but with MAP2's address in the Transmitter Address field.
>
> These anomalous Block Acks were sent because the MAC-ADDRESS-FILTER was misconfigured at MAP3, which caused that station to respond to addresses different than its own.  The reasons for this misconfiguration were:
>   (1) in mesh (and other) mode(s), the driver creates a hidden monitor vif along the mesh vif

At least since some 10.4 firmware, the hidden monitor vdev is no longer
required. See https://www.spinics.net/lists/linux-wireless/msg156475.html


>   (2) this second monitor vif is assigned the default mac address reported by the firmware (arvif->mac_addr)
>   (3) this mac address (which the driver was getting from the pre-cal files) is XOR'd with the mesh vif address to configure MAC-ADDRESS-FILTER
>   (4) once that happens, the hardware will ack all addresses that pass the MAC-ADDRESS-FILTER.  If the two mac addresses (vif->addr and arvif->mac_addr) are very dissimilar, that will result in a storm of invalid Block Acks
>
> We resolved the issue by patching the pre-cal data with the same address as the mesh interface, so that vif->addr == arvif->mac_addr.  This is more a workaround than a real fix, because this misconfiguration this MAC-ADDRESS-FILTER can easily go unnoticed.  In fact, what unblocked us on this issue was switching to Candela Tech's custom firmware and driver (ath10k-ct).  This provides a nice interface to the hardware registers:
>
> cat /debug/ieee80211/wiphy1/ath10k/fw_regs
>
>         ath10k Target Register Dump
>         =================
>         MAC-FILTER-ADDR-L32 0xffffffff
>         MAC-FILTER-ADDR-U16 0x0000ffff
>
> We would probably be still trying to solve this if Ben Greear did not point us in the right direction.
>
> Cheers,
>
> Javier
>
>
> On 2/7/18, 2:15 PM, "Javier Cardona" <jcardona at fb.com> wrote:
>
>     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
>
>
>
>
>
>
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-- 
thomas