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I was just wondering, every so often i receive a warning from my wlan watchdog, regarding some issues with the DMA TX queue

[  710.984380] ieee80211 phy0: rt2x00usb_watchdog_tx_dma: Warning - TX queue 2 DMA timed out, invoke forced forced reset
[  711.996050] ieee80211 phy0: rt2x00usb_watchdog_tx_dma: Warning - TX queue 2 DMA timed out, invoke forced forced reset

Doesn't really seem to cause any problem thus far, but as I understand it:

DMA stands for direct memory access so, the card must be writing a queue in memory with the information to be transmitted over.

So this warning is actually just telling me that at some point the system had to discard that queue to create a new one but it couldn't. Hence, the forced reset

Why do you think that might be? I mean if it is Direct memory, the only reason i could think of to not being able to release it, is that some other process was either reading or writing to the same address.

Is there a process reading out what I'm about to send out? why? which one?

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The warning describes the symptom (driver detected a timeout state that shouldn't have happened), but the cause is some bug in the driver/hardware behaviour and/or timing interaction, possibly with the rest of the OS. You'll need to read the driver code, understand the hardware in detail, and do some serious debugging to find out what actually goes wrong. (And if you could do that, you wouldn't have asked this question).

Best thing you can do is to file a bug with the driver developers, but this is likely a tough one.

Networking layers will re-request packets that are dropped, so it's unlikely that this bug will break something.

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  • Thanks, yes not up to solve it just yet, just wondering what it meant and hopefully learn something doing so. Feb 9, 2018 at 1:58

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