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Date: Thu, 31 Oct 2019 16:57:50 +0100
From: Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] dma/direct: turn ARCH_ZONE_DMA_BITS into a variable
Message-ID: <20191031155750.GA7394@lst.de>
References: <20191031152837.15253-1-nsaenzjulienne@suse.de> <20191031154759.GA7162@lst.de> <40d06d463c05d36968e8b64924d78f7794f8de50.camel@suse.de>
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To: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Cc: Christoph Hellwig <hch@lst.de>, Marek Szyprowski <m.szyprowski@samsung.com>, Robin Murphy <robin.murphy@arm.com>, Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, Michael Ellerman <mpe@ellerman.id.au>, Heiko Carstens <heiko.carstens@de.ibm.com>, Vasily Gorbik <gor@linux.ibm.com>, Christian Borntraeger <borntraeger@de.ibm.com>, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org, iommu@lists.linux-foundation.org

On Thu, Oct 31, 2019 at 04:53:13PM +0100, Nicolas Saenz Julienne wrote:
> > > +#define ARM64_ZONE_DMA_BITS	30
> > > +
> > >  /*
> > >   * We need to be able to catch inadvertent references to memstart_addr
> > >   * that occur (potentially in generic code) before arm64_memblock_init()
> > > @@ -424,6 +427,8 @@ void __init arm64_memblock_init(void)
> > >  	else
> > >  		arm64_dma_phys_limit = PHYS_MASK + 1;
> > >  
> > > +	zone_dma_bits = ARM64_ZONE_DMA_BITS;
> > > +
> > >  	reserve_crashkernel();
> > 
> > This actually adds a new limit, as there wasn't one before for arm64.
> 
> Well, as zone_dma_bits is only relevant in dma/direct when ZONE_DMA is defined
> I figured it doesn't matter if the variable is set conditionally to ZONE_DMA or
> not.

I'd much prefer that to do separately.