Re: Warning in brcms_c_wait_for_tx_completion

[Seth Forshee <seth.forshee@canonical.com>]

On Tue, Jul 03, 2012 at 06:50:37PM +0200, Arend van Spriel wrote:
> 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

Thanks for the update, Arend. Brad and I are eager to help in any way we
can, so please let us know if there's anything we can do to assist.

Seth