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

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Date:	Thu, 13 Aug 2015 16:25:05 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Christoph Hellwig <hch@....de>
Cc:	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 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.

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