linux-kernel - Re: [PATCH] powerpc: enable a 30-bit ZONE

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Date:   Fri, 14 Jun 2019 22:15:33 +0300
From:   Aaro Koskinen <aaro.koskinen@....fi>
To:     Mathieu Malaterre <malat@...ian.org>
Cc:     Christoph Hellwig <hch@....de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Larry Finger <Larry.Finger@...inger.net>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc: enable a 30-bit ZONE_DMA for 32-bit pmac

Hi,

On Fri, Jun 14, 2019 at 09:24:16AM +0200, Mathieu Malaterre wrote:
> On Thu, Jun 13, 2019 at 10:27 AM Christoph Hellwig <hch@....de> wrote:
> > With the strict dma mask checking introduced with the switch to
> > the generic DMA direct code common wifi chips on 32-bit powerbooks
> > stopped working.  Add a 30-bit ZONE_DMA to the 32-bit pmac builds
> > to allow them to reliably allocate dma coherent memory.
> >
> > Fixes: 65a21b71f948 ("powerpc/dma: remove dma_nommu_dma_supported")
> > Reported-by: Aaro Koskinen <aaro.koskinen@....fi>
> > Signed-off-by: Christoph Hellwig <hch@....de>
> > ---
> >  arch/powerpc/include/asm/page.h         | 7 +++++++
> >  arch/powerpc/mm/mem.c                   | 3 ++-
> >  arch/powerpc/platforms/powermac/Kconfig | 1 +
> >  3 files changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/include/asm/page.h b/arch/powerpc/include/asm/page.h
> > index b8286a2013b4..0d52f57fca04 100644
> > --- a/arch/powerpc/include/asm/page.h
> > +++ b/arch/powerpc/include/asm/page.h
> > @@ -319,6 +319,13 @@ struct vm_area_struct;
> >  #endif /* __ASSEMBLY__ */
> >  #include <asm/slice.h>
> >
> > +/*
> > + * Allow 30-bit DMA for very limited Broadcom wifi chips on many powerbooks.
> 
> nit: would it be possible to mention explicit reference to b43-legacy.
> Using b43 on my macmini g4 never showed those symptoms (using
> 5.2.0-rc2+)

According to Wikipedia Mac mini G4 is limited to 1 GB RAM, so that's
why you don't see the issue.

A.