linux-kernel - Re: [PATCH 5/5] dma-mapping: consolidate dma_set

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Date:	Thu, 13 Aug 2015 19:58:14 +0200
From:	Christoph Hellwig <hch@....de>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Christoph Hellwig <hch@....de>, akpm@...ux-foundation.org,
	arnd@...db.de, catalin.marinas@....com, will.deacon@....com,
	ysato@...rs.sourceforge.jp, monstr@...str.eu, jonas@...thpole.se,
	cmetcalf@...hip.com, gxt@...c.pku.edu.cn, x86@...nel.org,
	linux-alpha@...r.kernel.org, linux-hexagon@...r.kernel.org,
	linux-ia64@...r.kernel.org, linux-mips@...ux-mips.org,
	linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
	linux-sh@...r.kernel.org, sparclinux@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] dma-mapping: consolidate dma_set_mask

On Thu, Aug 13, 2015 at 04:25:05PM +0100, Russell King - ARM Linux wrote:
> On Thu, Aug 13, 2015 at 05:04:08PM +0200, Christoph Hellwig wrote:
> > diff --git a/arch/arm/common/dmabounce.c b/arch/arm/common/dmabounce.c
> > index 1143c4d..260f52a 100644
> > --- a/arch/arm/common/dmabounce.c
> > +++ b/arch/arm/common/dmabounce.c
> > @@ -440,14 +440,6 @@ static void dmabounce_sync_for_device(struct device *dev,
> >  	arm_dma_ops.sync_single_for_device(dev, handle, size, dir);
> >  }
> >  
> > -static int dmabounce_set_mask(struct device *dev, u64 dma_mask)
> > -{
> > -	if (dev->archdata.dmabounce)
> > -		return 0;
> > -
> > -	return arm_dma_ops.set_dma_mask(dev, dma_mask);
> 
> Are you sure about this?  A user of dmabounce gets to request any mask
> with the original code (even though it was never written back... which
> is a separate bug.)  After this, it seems that this will get limited
> by the dma_supported() check.  As this old code is about bouncing any
> buffer into DMA-able memory, it doesn't care about the DMA mask.

I think you're right.  With the default dma_supported implementation
it would be fine, but ARM uses a custom one.  I'll keep the arm
specific dma_set_mask implementation for the next round.
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