linux-kernel - Re: [PATCH 4/7] swiotlb: Allow arch override of address_needs

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Date:	Fri, 10 Apr 2009 04:50:10 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	jeremy@...p.org
Cc:	fujita.tomonori@....ntt.co.jp, galak@...nel.crashing.org,
	hch@...radead.org, linux-kernel@...r.kernel.org, mingo@...e.hu,
	ian.campbell@...rix.com, beckyb@...nel.crashing.org
Subject: Re: [PATCH 4/7] swiotlb: Allow arch override of
 address_needs_mapping

On Thu, 09 Apr 2009 12:19:19 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> FUJITA Tomonori wrote:
> >> Well, Becky's patches also added the hwdev argument to them, so 
> >> presumably the powerpc implementation needs that (different 
> >> devices/buses have differing views of physical memory, I guess).
> >>     
> >
> > Until I see the ppc specific swiotlb patchset, I'm not sure but I
> > think that we can remove phys_to_bus in swiotlb.
> >   
> 
> Kumar's comment was: "For our SoC chips we don't need any mapping 
> between phys & bus.  However something like PCI does have a mapping (a 
> simple offset)."
> 
> Kumar, could a single system have different phys<->bus mappings on a 
> single system, or could it differ from device to device (or bus to bus)?
> 
> > Even if we need phys_to_bus, we can remove the rest of __weak tricks
> > for only dom0. And we can make phys_to_bus arch-specific. Then we
> > don't need any __weak tricks in swiotlb (and x86's swiotlb). dom0
> > support adds many hacks to swiotlb.
> >   
> 
> Well, we'd still need a way to do hook the swiotlb_alloc(_boot) 
> allocation.  At the moment its effectively arch-specific because x86 
> only uses swiotlb_alloc_boot(), and ia64 only uses swiotlb_alloc().  One 

Hmm, I think that ia64 use swiotlb_alloc_boot too.

ia64 uses swiotlb in two ways; using only swiotlb, using swiotlb and
hw iommu. The latter is similar what x86 Calgary does.

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