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Message-ID: <fdfc817d1dcdc83f5bc45f0ab12cbce0c61e6702.camel@kernel.crashing.org>
Subject: Re: [BISECTED REGRESSION] b43legacy broken on G4 PowerBook
From:   Benjamin Herrenschmidt <benh@kernel.crashing.org>
To:     Christoph Hellwig <hch@lst.de>
Cc:     Larry Finger <Larry.Finger@lwfinger.net>,
        Aaro Koskinen <aaro.koskinen@iki.fi>,
        Christian Zigotzky <chzigotzky@xenosoft.de>,
        Michael Ellerman <mpe@ellerman.id.au>,
        linuxppc-dev@lists.ozlabs.org, linux-wireless@vger.kernel.org,
        linux-kernel@vger.kernel.org
Date:   Tue, 11 Jun 2019 16:58:12 +1000
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On Tue, 2019-06-11 at 08:08 +0200, Christoph Hellwig wrote:
> On Tue, Jun 11, 2019 at 03:56:33PM +1000, Benjamin Herrenschmidt
> wrote:
> > The reason I think it sort-of-mostly-worked is that to get more
> > than
> > 1GB of RAM, those machines use CONFIG_HIGHMEM. And *most* network
> > buffers aren't allocated in Highmem.... so you got lucky.
> > 
> > That said, there is such as thing as no-copy send on network, so I
> > wouldn't be surprised if some things would still have failed, just
> > not
> > frequent enough for you to notice.
> 
> Unless NETIF_F_HIGHDMA is set on a netdev, the core networkign code
> will bounce buffer highmem pages for the driver under all
> circumstances.

 ... which b43legacy doesn't set to the best of my knowledge ...

Which makes me wonder how come it didn't work even with your patches ?
AFAIK, we have less than 1GB of lowmem unless the config has been
tweaked....

Cheers,
Ben.