Atheros AR9287 2.4 GHz Wifi drops out frequently

Hi everybody!

I’ve been owning a Turris Omnia 2020 for a couple of months and generally speaking, I’m very happy about my investment!

Unfortunately I noticed that 2,4 GHz Wifi drops out from time to time. That means: Clients lose Wifi connection and won’t reconnect successfully. Instead, the client’s network adapter needs to be restarted (or device rebooted) or the 2,4 GHz adapter of the Turris Omnia needs to be restartet. It seems like Wifi communication is “stuck”. When looking at the syslog (or kernel log), I see the following just when the issue occurs:

[226722.571131] ath: phy1: DMA failed to stop in 10 ms AR_CR=0x00000024 AR_DIAG_SW=0x42100020 DMADBG_7=0x00008040
[226722.980705] ath: phy1: DMA failed to stop in 10 ms AR_CR=0x00000024 AR_DIAG_SW=0x42100020 DMADBG_7=0x00008040
[226723.390306] ath: phy1: DMA failed to stop in 10 ms AR_CR=0x00000024 AR_DIAG_SW=0x42100020 DMADBG_7=0x00004040
[226723.799881] ath: phy1: DMA failed to stop in 10 ms AR_CR=0x00000024 AR_DIAG_SW=0x42100020 DMADBG_7=0x00008040
[226724.209449] ath: phy1: DMA failed to stop in 10 ms AR_CR=0x00000024 AR_DIAG_SW=0x42100020 DMADBG_7=0x00006040
[226724.619045] ath: phy1: DMA failed to stop in 10 ms AR_CR=0x00000024 AR_DIAG_SW=0x42100020 DMADBG_7=0x00006040
[226725.028612] ath: phy1: DMA failed to stop in 10 ms AR_CR=0x00000024 AR_DIAG_SW=0x42100020 DMADBG_7=0x00008040
[226725.438202] ath: phy1: DMA failed to stop in 10 ms AR_CR=0x00000024 AR_DIAG_SW=0x42100020 DMADBG_7=0x00008040
[...]

These are the only lines that are logged - no more error messages or other hints what might be wrong.

The problem occurs randomly - I could not reproduce it on purpose. Sometimes it happens more frequently than usual.

My Turris Omnia has the latest updates (TurrisOS 5.1.10 a5672f6b96f393145070ad17c8eb1d15ef49ad2e) and was only slightly modified: I inserted a mSATA SSD to PCIe slot 1, put the 5 GHz Wifi card into slot 2 and the 2,4 GHz card is in slot 3 (near the edge of the case).

As I cannot find any pattern with this issue, I’m seeking help here. Is there anybody facing the same or similar issues?

The problem does only occur on 2,4 GHz Wifi with different devices (Windows 10 laptop, iPhone, iPad, Android phone). 5 GHz Wifi is totally fine.

I’ve tried

  • switching Wifi channels
  • switching from 40 MHz channel width to 20 MHz.
  • heavy use of USB 3.0 slot (there are reports that USB interferes with 2.4 GHz wifi - I could not find a problem)

Update 2021-04-01:
I might have fixed it by setting the adapter from HT40 mode to HT 20 mode (20 MHz bandwidth) and restarting + reconnecting all devices. The Wifi has been stable for a few days, now. It might be related to this: https://svn.dd-wrt.com/ticket/2952?cversion=0&cnum_hist=73#comment:110