Messages in this thread | | | Date | Wed, 17 Sep 2008 02:13:25 +0900 | Subject | Re: [PATCH 0/3] fix GART to respect device's dma_mask about virtual mappings | From | FUJITA Tomonori <> |
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On Tue, 16 Sep 2008 15:43:35 +0200 Andi Kleen <andi@firstfloor.org> wrote:
> > What the need_iommu() does is seeing if GART needs to do virtual > > mappings or not. > > > > (After need_iommu() checking) What this patchset does is to guarantee > > that GART provides a virtual address that a device can access to. > > Ah you care about masks < 32bit?
Yes,
> Those always are handled elsewhere in the block layer (using the bounce_pfn > mechanism)
I don't think that the bounce guarantees that dma_alloc_coherent() returns an address that a device can access to.
> or in various other ways in other subsystems. e.g. on networking > the rule is that you just don't announce direct SG when you have > less than 32bit mask.
I'm not familiar with what the networking does, for example, seems that b44 sets dev->dma_mask to DMA_30BIT_MASK and b44_start_xmit() does:
mapping = ssb_dma_map_single(bp->sdev, skb->data, len, DMA_TO_DEVICE); if (ssb_dma_mapping_error(bp->sdev, mapping) || mapping + len > DMA_30BIT_MASK) { struct sk_buff *bounce_skb;
/* Chip can't handle DMA to/from >1GB, use bounce buffer */ if (!ssb_dma_mapping_error(bp->sdev, mapping)) ssb_dma_unmap_single(bp->sdev, mapping, len, DMA_TO_DEVICE);
IOMMUs can try to return an address that the NIC can access to.
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