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Date:   Tue, 11 Jun 2019 09:53:58 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc:     Christoph Hellwig <hch@lst.de>,
        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
Subject: Re: [BISECTED REGRESSION] b43legacy broken on G4 PowerBook
Message-ID: <20190611075358.GA21815@lst.de>
References: <20190605225059.GA9953@darkstar.musicnaut.iki.fi> <73da300c-871c-77ac-8a3a-deac226743ef@lwfinger.net> <7697a9d10777b28ae79fdffdde6d0985555f6310.camel@kernel.crashing.org> <3ed1ccfe-d7ca-11b9-17b3-303d1ae1bb0f@lwfinger.net> <c91ccbddd6a58dbee5705f10ed1d98fb44bd8f8d.camel@kernel.crashing.org> <20190611060816.GA20158@lst.de> <fdfc817d1dcdc83f5bc45f0ab12cbce0c61e6702.camel@kernel.crashing.org>
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On Tue, Jun 11, 2019 at 04:58:12PM +1000, Benjamin Herrenschmidt wrote:
>  ... 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....

It needs to bounce to somewhere.  And the dma-direct code is pretty
strict to require a zone it can do allocations from when setting the
dma mask.  As was the old ppc64 code, but not the ppc32 code that
allowed setting any DMA mask.  And something about the more strict
validation seem to trip up now.