linux-kernel - Re: pci_map_sg() does not coalesce adjacent physical memory? x86

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Message-Id: <20081119160547G.fujita.tomonori@lab.ntt.co.jp>
Date:	Wed, 19 Nov 2008 16:05:07 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	leon.woestenberg@...il.com
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	James.Bottomley@...senpartnership.com, tj@...nel.org
Subject: Re: pci_map_sg() does not coalesce adjacent physical memory? x86

Oops, sorry about typos.

On Wed, 19 Nov 2008 15:58:12 +0900
FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:

> > Of course, I could write my own (tm) and map my pages into PCI using
> > pci_map_single, but I thought I was being the good kid by using what
> > was there.
> 
> I don't think it's not a good place. What pci_map_single should do is
> mapping a virtual address to a dma-capable address.
> 
> IOMMU dma operations maps a virtual address to an I/O address and
> non-IOMMU dma operations do nothing. As you said below, some IOMMU
> operations do coalescing but it's virtual mapping (probably their code
                                    virtual coalescing

> can handle physical coalescing too though but the block layer does
> physical coalescing before that though). And the virtual mapping is
                                                   virtual coalescing

> optional. Not all the IOMMU operations do. As I said, x86 IOMMUs
> (VT-d, AMD, and Calgary) except for GART does not do coalescing. Any
> non-IOMMU dma operations don't do something complicated.
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