Date: Fri, 30 Jan 2009 07:54:07 +0900
From: Yasunori Goto <y-goto@jp.fujitsu.com>
To: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Subject: Re: [PATCH -tip 1/3] IA64: fix swiotlb alloc_coherent for non DMA_64BIT_MASK devices
Cc: mingo@elte.hu, tony.luck@intel.com, linux-kernel@vger.kernel.org,
       linux-ia64@vger.kernel.org
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References: <20090129200303.E2C2.E1E9C6FF@jp.fujitsu.com> <20090129205446N.fujita.tomonori@lab.ntt.co.jp>
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> On Thu, 29 Jan 2009 20:41:07 +0900
> Yasunori Goto <y-goto@jp.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@lab.ntt.co.jp>
> > > Cc: Yasunori Goto <y-goto@jp.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.

I tested your patch, but, ia64_swiotlb_alloc_coherent() was not called with
CONFIG_GENERIC.

swiotlb_dma_ops is set by pci_swiotlb_init().
However, it seems to be not called when CONFIG_IA64_DIG/Generic configuration.


> > > This patch is sorta updated version of:
> > > 
> > > http://marc.info/?l=linux-kernel&m=122638215612705&w=2
> > > 

This old version is effective even CONFIG_GENERIC/CONFIG_IA64_DIG.

Bye.

> 
> 
> > 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?


-- 
Yasunori Goto 


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