linux-kernel - Re: [PATCH 2/2] IOMMU Identity Mapping Support: Intel IOMMU implementation

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Date:	Thu, 18 Jun 2009 13:02:56 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	"Yu, Fenghua" <fenghua.yu@...el.com>
Cc:	"'Chris Wright'" <chrisw@...s-sol.org>,
	"'David Woodhouse'" <dwmw2@...radead.org>,
	"'Linus Torvalds'" <torvalds@...ux-foundation.org>,
	"'Stephen Rothwell'" <sfr@...b.auug.org.au>,
	"'Andrew Morton'" <akpm@...ux-foundation.org>,
	"'Ingo Molnar'" <mingo@...e.hu>,
	"'Christopher Wright'" <chrisw@...hat.com>,
	"Kay, Allen M" <allen.m.kay@...el.com>,
	"'iommu'" <iommu@...ts.linux-foundation.org>,
	"'lkml'" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] IOMMU Identity Mapping Support: Intel IOMMU
	implementation

* Yu, Fenghua (fenghua.yu@...el.com) wrote:
> >> @@ -2259,6 +2394,9 @@ static dma_addr_t __intel_map_single(struct device
> >*hwdev, phys_addr_t paddr,
> >>  	int ret;
> >>  	struct intel_iommu *iommu;
> >>
> >> +	if (identity_list(pdev))
> >> +		return paddr;
> >> +
> >
> >This is same as DUMMY_DEVICE_DOMAIN_INFO.  Please consolidate to a test
> >that just says "do i need translation".
> >
> 
> The purpose of identity_list() is to have an interface for future when we need to set 1:1 mapping on some specific devices instead of all (just like Muli Ben-Yehuda suggested earlier in this thread).
> 
> Right now it's almost empty. Yeah, I can change this checking to simply:
> if (iommu_identity_mapping)
> 	return paddr;
> 

That's fine, I figured that's why you had the list check.  But my point is
there are 2 ways to test for the same thing, which is whether a translation
is needed or not.

So a simple helper to help clarify what is going on.  Like this:

static int iommu_dummy(struct pci_device *pdev)
{
	return (pdev->dev.archdata.iommu == DUMMY_DEVICE_DOMAIN_INFO);
}

static int iommu_no_mapping(struct pci_device *pdev)
{
	if (identity_list(pdev) || iommu_dummy(pdev))
		return 1;
	return 0;
}

> >And what about DMA mask smaller than physical memory.  The PT mode drops
> >back to swiotlb iirc.

Also...this?
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