linux-kernel - Re: [PATCH -tip 1/3] IA64: fix swiotlb alloc_coherent for non DMA_64BIT

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Date:	Thu, 29 Jan 2009 20:54:41 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	y-goto@...fujitsu.com
Cc:	fujita.tomonori@....ntt.co.jp, mingo@...e.hu, tony.luck@...el.com,
	linux-kernel@...r.kernel.org, linux-ia64@...r.kernel.org
Subject: Re: [PATCH -tip 1/3] IA64: fix swiotlb alloc_coherent for non
 DMA_64BIT_MASK devices

On Thu, 29 Jan 2009 20:41:07 +0900
Yasunori Goto <y-goto@...fujitsu.com> wrote:

> > Before the dma ops unification, IA64 always uses GFP_DMA for
> > dma_alloc_coherent like:
> > 
> > #define dma_alloc_coherent(dev, size, handle, gfp)	\
> > 	platform_dma_alloc_coherent(dev, size, handle, (gfp) | GFP_DMA)
> > 
> > This GFP_DMA enforcement doesn't make sense for IOMMUs since they can
> > do address translation to give addresses that devices can access
> > to. The IOMMU drivers ignore the zone flag. However, this is still
> > necessary for swiotlb since it can't do address translation.
> > 
> > We don't always need to use GFP_DMA for swiotlb. We need GFP_DMA for
> > devices incapable of 64bit DMA.
> > 
> > This patch is sorta updated version of:
> > 
> > http://marc.info/?l=linux-kernel&m=122638215612705&w=2
> > 
> > Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> > Cc: Yasunori Goto <y-goto@...fujitsu.com>
> > ---
> >  arch/ia64/kernel/pci-swiotlb.c |   10 +++++++++-
> >  1 files changed, 9 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/ia64/kernel/pci-swiotlb.c b/arch/ia64/kernel/pci-swiotlb.c
> > index 717ad4f..573f02c 100644
> > --- a/arch/ia64/kernel/pci-swiotlb.c
> > +++ b/arch/ia64/kernel/pci-swiotlb.c
> > @@ -13,8 +13,16 @@
> >  int swiotlb __read_mostly;
> >  EXPORT_SYMBOL(swiotlb);
> >  
> > +static void *ia64_swiotlb_alloc_coherent(struct device *dev, size_t size,
> > +					 dma_addr_t *dma_handle, gfp_t gfp)
> > +{
> > +	if (dev->coherent_dma_mask != DMA_64BIT_MASK)
> > +		gfp |= GFP_DMA;
> > +	return swiotlb_alloc_coherent(dev, size, dma_handle, gfp);
> > +}
> > +
> >  struct dma_map_ops swiotlb_dma_ops = {
> > -	.alloc_coherent = swiotlb_alloc_coherent,
> > +	.alloc_coherent = ia64_swiotlb_alloc_coherent,
> >  	.free_coherent = swiotlb_free_coherent,
> >  	.map_page = swiotlb_map_page,
> >  	.unmap_page = swiotlb_unmap_page,
> > -- 
> > 1.6.0.6
> 
> 
> Though I may be misunderstanding something, this initialization seems to be
> called only when CONFIG_IA64_DIG_VTD is on.

Hmm, what's 'this initialization'?

This patch always sets swiotlb_dma_ops.alloc_coherent to
ia64_swiotlb_alloc_coherent.


> CONFIG_IA64_DIG_VTD
>   platform_dma_init() -> pci_iommu_alloc() -> pci_swiotlb_init()
> 
> CONFIG_IA64_DIG/CONFIG_IA64_GENERIC
>   platform_dma_init() -> swiotlb_dma_init()
> 
> Is it intended? 
> Do you wish GFP_DMA should be always ON when generic config?
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