Re: Warning in brcms_c_wait_for_tx_completion

["Arend van Spriel" <arend@broadcom.com>]

On 07/03/2012 03:45 PM, Seth Forshee wrote:
> Hi Arend,
> 
> This message is off-list, only because I know it's been discussed
> on-list in the past. Feel free to pull in any individuals or mailing
> lists if you wish.

The issue is popping up regularly in Fedora 17. See [1]

> Brad (on Cc) just received a MacBook Air with BCM4313 wireless, and he's
> able to very reliably trigger the WARN_ON_ONCE in
> brcms_c_wait_for_tx_completion() in his environment. He also gets an
> endless stream of these messages when wireless drops out.
> 
>   ieee80211 phy0: brcms_c_prec_enq_head: No where to go, prec == 4

I only seen this regularly with Fedora 17. Ubuntu 11.04 with 3.5-rc4
installed in our smoketest setups does not show it. Basically, it means
that packet queue in our driver is full and packets are dropped. As we
do not inform mac80211 that traffic is stalled this is expected to happen.

> This is in the 3.5-rc kernels. We're carrying the regulatory patches, in
> the Ubuntu kernel, but Brad tested an older rc without the patches and
> still gets this.
> 
> We've done a little debugging and have found a couple of points. First,
> all the stack traces I've seen from Brad's machine show that the warning
> triggers during a scan. Second, we added debug to brcms_b_mute() to
> check whether tx was somehow getting muted in the driver without being
> unmuted, but this is not the case.

I did a little debugging as well and also concluded a scan triggers it.
I change the WARN_ON_ONCE to a WARN_ON and it seems to correlate with
the duration between scan_start and scan_complete. When it is in 8-10
sec. range the warning kicks in. I was going to add debugging for the tx
mute.

> I wanted to get in touch with you in case there was anything you wanted
> Brad to try to help with identifying the cause of this issue. Also you
> can find details of his AP setup below.

The issue is either driver related or caused by firmware behaviour. I
suspect the firmware, but I have not 100% certainty yet.

Gr. AvS

[1] https://bugzilla.redhat.com/show_bug.cgi?id=799168