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

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Date:	Thu, 9 Apr 2009 08:01:18 +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 Wed, 08 Apr 2009 15:36:58 -0700
Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> FUJITA Tomonori wrote:
> >> Some architectures need non-trivial bus<->phys conversion routines, etc, 
> >>     
> >
> > Only Xen needs such conversion for swiotlb.
> >   
> 
> 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.

About __weak address_needs_mapping function, as I said, removing it
and using dma_map_ops is a proper solution.


> >> so either we can require it that all architectures wishing to use 
> >> swiotlb define these functions, or have weak default functions that can 
> >> be overridden by architectures where necessary.
> >>     
> >
> > Can you give an example? I don't think IA64, X86_64 or POWER (which
> > will use swiotlb) need any __weak functions. If you say other archs
> > could use swiotlb, please tell me how they need these __weak.
> >   
> 
> As I said, Becky's patches added hooks in many of the places we added 
> them for Xen.  I assume that's because powerpc needs them; I have not 
> seen the arch/powerpc side of those changes.
> 
>     J
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