Bug 3398

I'm entering this to document a workaround for a fairly serious problem with the Broadcom brcmsmac wireless driver.

The specific case concerns an Acer Aspire One 722 with a Broadcom BCM4313 wireless chip.  This chip is unique in that according to the linux-wireless site it is the only Broadcom chip not supported by the b43 driver.  However, they have a link to a Broadcom page for a Broadcom-produced driver called brcmsmac that handles that chip and a few others.

Mageia packages the brcmsmac driver in the "staging" area of the kernel and it blacklists the brcm80211 driver which was the previous name of brcmsmac.  I'm guessing that it does this only if the BCM4313 is detected, presumably because there's a stable version of brcm80211 in the regular drivers tree that is known not to work with the BCM4313.

The specific symptom is that, with the wireless interface defined through drakconnect as wlan0, the system will behave nicely as long as the wired eth0 interface is active (cable plugged in, linkup).  If you unplug the cable so that the wireless becomes the operative interface the system will freeze hard, ignoring even Alt-SysRq-B, within a few seconds.  If you attempt to boot the system without the eth0 cable plugged and available, you probably won't even make it to the DM screen before it freezes.

If you google this without limiting the search to the past year you'll get a lot of outdated hits about freezes which may or may not apply.

One of them says to blacklist the acer-wmi driver.  Another says to blacklist the b43 driver so that you're sure of getting the brcmsmac driver, and that the two don't get along if loaded together.  I did both of these things without effect.

The actual solution came from https://bugzilla.novell.com/show_bug.cgi?id=676785 down towards the bottom.  Apparently there is a conflict between the brcmsmac driver and the atl1c driver used for the wired ethernet  If you blacklist atl1c and set ONBOOT=no in ifcfg-eth0 and reboot without the eth0 cable plugged in, things will be picture-perfect.

I have not yet backtracked to see which of the blacklists is critical to the problem and which is not.  I was configuring the machine for someone else and wanted to get it into their hands ASAP.  For now, people trying to put cauldron on this machine should blacklist acer-wmi, b43, and atl1c.  That will get you wireless, but no ethernet.  It may be that blacklisting brcmsmac and leaving atl1c alone will get you ethernet but no wireless, but I haven't verified that yet.

There was also a suggestion in the above link that if you waited until brcmsmac had initialized to modprobe atl1c you'd have both working, but I haven't verified that either.

If the upstream devs know about this, then it's probably not worth the trouble of refining this workaround, unless someone finds it wanting.