[BISECTED REGRESSION] b43legacy broken on G4 PowerBook

[Benjamin Herrenschmidt]

On Thu, 2019-06-06 at 20:56 +1000, Benjamin Herrenschmidt wrote:
> On Thu, 2019-06-06 at 12:31 +0300, Aaro Koskinen wrote:
> > Hi,
> > 
> > On Thu, Jun 06, 2019 at 10:54:51AM +1000, Benjamin Herrenschmidt
> > wrote:
> > > On Thu, 2019-06-06 at 01:50 +0300, Aaro Koskinen wrote:
> > > > Hi,
> > > > 
> > > > When upgrading from v5.0 -> v5.1 on G4 PowerBook, I noticed WLAN
> > > > does
> > > > not work anymore:
> > > > 
> > > > [   42.004303] b43legacy-phy0: Loading firmware version 0x127,
> > > > patch level 14 (2005-04-18 02:36:27)
> > > > [   42.184837] b43legacy-phy0 debug: Chip initialized
> > > > [   42.184873] b43legacy-phy0 ERROR: The machine/kernel does not
> > > > support the required 30-bit DMA mask
> > > > 
> > > > The same happens with the current mainline.
> > > 
> > > How much RAM do you have ?
> > 
> > The system has 1129 MB RAM. Booting with mem=1G makes it work.
> 
> Wow... that's an odd amount. One thing we could possibly do is add code
> to limit the amount of RAM when we detect that device....

Sent too quickly... I mean that *or* force swiotlb at 30-bits on those systems based
on detecting the presence of that device in the device-tree.

Cheers,
Ben.