Re: [PATCH 4/7] swiotlb: Allow arch override of address_needs_mapping

[Kumar Gala]

On Apr 8, 2009, at 7:09 PM, Jeremy Fitzhardinge wrote:

> FUJITA Tomonori wrote:
> > On Wed, 08 Apr 2009 16:16:17 -0700
> > Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
> >
> >
> > > FUJITA Tomonori wrote:
> > >
> > > > > Becky's patches of last week also added __weak annotations to  
> > > > > swiotlb_bus_to_virt, virt_to_bus and bus_to_phys; added the  
> > > > > hwdev parameter to swiotlb_bus_to_phys; and added a weak  
> > > > > swiotlb_arch_address_needs_mapping.  I assume that was needed  
> > > > > because powerpc needs non-trivial implementations for those  
> > > > > functions.
> > > > Hmm, what she added are wrappers of virt_to_bus and bus_to_virt. We
> > > > can remove these and directly use virt_to_bus and bus_to_virt.
> > > In general those interfaces are deprecated.  Are we un-deprecating  
> > > them?  Or do you mean adding virt<->bus to dma_ops?
> >
> > Hmm, these interfaces are wrong for drivers surely because they can't
> > handle dma mapping properly. However, they are exactly what swiotlb
> > needs (swiotlb doesn't need to care about dma mapping).
>
> It needs to care about the mapping from phys to bus.  On x86 they're  
> identical, but on powerpc there can be at least an offset between  
> them.
>
> > Until 2.6.28,
> > swiotlb has used them. They are with IA64, X86_64 and PPC_32, I  
> > think.
>
> 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).

On powerpc we need the hwdev because things vary based on bus.  For  
our SoC chips we don't need any mapping between phys & bus.  However  
something like PCI does have a mapping (a simple offset).

- k
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