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

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Message-ID: <a5fc355e44fb5edea41274329f7c5d04a8dff6fc.camel@kernel.crashing.org>
Date:   Wed, 19 Jun 2019 23:31:44 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Christoph Hellwig <hch@....de>, paulus@...ba.org
Cc:     Larry.Finger@...inger.net, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org, aaro.koskinen@....fi
Subject: Re: [PATCH] powerpc: enable a 30-bit ZONE_DMA for 32-bit pmac

On Wed, 2019-06-19 at 22:32 +1000, Michael Ellerman wrote:
> Christoph Hellwig <hch@....de> writes:
> > Any chance this could get picked up to fix the regression?
> 
> Was hoping Ben would Ack it. He's still powermac maintainer :)
> 
> I guess he OK'ed it in the other thread, will add it to my queue.

Yeah ack. If I had written it myself, I would have made the DMA bits a
variable and only set it down to 30 if I see that device in the DT
early on, but I can't be bothered now, if it works, ship it :-)

Note: The patch affects all ppc32, though I don't think it will cause
any significant issue on those who don't need it.

Cheers,
Ben.

> cheers
> 
> > On Thu, Jun 13, 2019 at 10:24:46AM +0200, Christoph Hellwig 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.
> > > + */
> > > +#ifdef CONFIG_PPC32
> > > +#define ARCH_ZONE_DMA_BITS 30
> > > +#else
> > >  #define ARCH_ZONE_DMA_BITS 31
> > > +#endif
> > >  
> > >  #endif /* _ASM_POWERPC_PAGE_H */
> > > diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c
> > > index cba29131bccc..2540d3b2588c 100644
> > > --- a/arch/powerpc/mm/mem.c
> > > +++ b/arch/powerpc/mm/mem.c
> > > @@ -248,7 +248,8 @@ void __init paging_init(void)
> > >  	       (long int)((top_of_ram - total_ram) >> 20));
> > >  
> > >  #ifdef CONFIG_ZONE_DMA
> > > -	max_zone_pfns[ZONE_DMA]	= min(max_low_pfn, 0x7fffffffUL
> > > >> PAGE_SHIFT);
> > > +	max_zone_pfns[ZONE_DMA]	= min(max_low_pfn,
> > > +			((1UL << ARCH_ZONE_DMA_BITS) - 1) >>
> > > PAGE_SHIFT);
> > >  #endif
> > >  	max_zone_pfns[ZONE_NORMAL] = max_low_pfn;
> > >  #ifdef CONFIG_HIGHMEM
> > > diff --git a/arch/powerpc/platforms/powermac/Kconfig
> > > b/arch/powerpc/platforms/powermac/Kconfig
> > > index f834a19ed772..c02d8c503b29 100644
> > > --- a/arch/powerpc/platforms/powermac/Kconfig
> > > +++ b/arch/powerpc/platforms/powermac/Kconfig
> > > @@ -7,6 +7,7 @@ config PPC_PMAC
> > >  	select PPC_INDIRECT_PCI if PPC32
> > >  	select PPC_MPC106 if PPC32
> > >  	select PPC_NATIVE
> > > +	select ZONE_DMA if PPC32
> > >  	default y
> > >  
> > >  config PPC_PMAC64
> > > -- 
> > > 2.20.1
> > 
> > ---end quoted text---