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

FUJITA Tomonori
2009-01-29T11:54:41Z

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\x122638215612705&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.

> 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?