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Date:   Sat, 8 Jun 2019 09:23:22 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc:     Larry Finger <Larry.Finger@lwfinger.net>,
        Aaro Koskinen <aaro.koskinen@iki.fi>,
        Christoph Hellwig <hch@lst.de>,
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        linux-kernel@vger.kernel.org
Subject: Re: [BISECTED REGRESSION] b43legacy broken on G4 PowerBook
Message-ID: <20190608072322.GA18896@lst.de>
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On Sat, Jun 08, 2019 at 02:21:23PM +1000, Benjamin Herrenschmidt wrote:
> 
> > Please try the attached patch. I'm not really pleased with it and I will 
> > continue to determine why the fallback to a 30-bit mask fails, but at least this 
> > one works for me.
> 
> Your patch only makes sense if the device is indeed capable of
> addressing 31-bits.
> 
> So either the driver is buggy and asks for a too small mask in which
> case your patch is ok, or it's not and you're just going to cause all
> sort of interesting random problems including possible memory
> corruption.

Well, my patches changes ZONE_DMA to be 30-bits instead of 31, and
thus should allow requesting a 30-bit mask to succeed.