linux-kernel - Re: swiotlb: remove __weak hooks in favour of architecture-specific functions

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Message-ID: <1242992596.22654.273.camel@zakaz.uk.xensource.com>
Date:	Fri, 22 May 2009 12:43:16 +0100
From:	Ian Campbell <Ian.Campbell@...citrix.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	"jeremy@...p.org" <jeremy@...p.org>,
	"beckyb@...nel.crashing.org" <beckyb@...nel.crashing.org>,
	"okir@...e.de" <okir@...e.de>, "mingo@...e.hu" <mingo@...e.hu>,
	"gregkh@...e.de" <gregkh@...e.de>,
	"xendevel@...ts.xensource.com" <xendevel@...ts.xensource.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: swiotlb: remove __weak hooks in favour of
	architecture-specific functions

On Fri, 2009-05-22 at 07:13 -0400, FUJITA Tomonori wrote:
> On Thu, 21 May 2009 17:15:21 +0100
> Ian Campbell <ian.campbell@...rix.com> wrote:
> Please go with the following way (that I posted yesterday):
> 
> http://marc.info/?l=xen-devel&m=124292666214380&w=2
> 
> 
> Export the core feature of swiotlb, managing iotlb buffer and
> implement the Xen mapping functions.

I feel that should be a last resort, before we go down that path we
should try and find a way for us to use the generic code in a clean way
which makes everyone happy.

We have had several attempts at this and admittedly have not yet come up
with something that satisfies everyone but I don't really think we have
gotten to the point of admitting defeat and just duplicating the code.

I think the proposal to use a dma_map_range-like function which I sent a
few minutes ago I think gets us closer to something which satisfies
everyone's requirements, including yours for a clean abstraction.

>  With that approach, there is not
> much code duplication and there is no need for ugly hooks for dom0;
> the phys/bus address conversion and address checking.

The phys/bus address conversion is also needed for powerpc.

I think the two address checking functions can be collapsed into a
single one which satisfies the needs of both Xen and powerpc.

What dom0 specific "ugly" hooks does that leave? The alloc one? I've
discussed that in another mail.

Ian.

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