Re: [PATCH -tip 1/3] IA64: fix swiotlb alloc_coherent for non DMA_64BIT_MASK devices

Yasunori Goto
2009-01-29T11:41:07Z

> 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.

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?

Bye.

--
Yasunori Goto