Re: [PATCH] powerpc: enable a 30-bit ZONE_DMA for 32-bit pmac

[Larry Finger]

On 6/14/19 2:15 PM, Aaro Koskinen wrote:
> 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@xxxxxx> 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@xxxxxx>
> > > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> > > ---
> > >   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.

He wouldn't see it with b43. Those cards have 32-bit DMA.

Larry