linux-kernel - Re: [LKML] Re: [PATCH] swiotlb v0.6: seperation of physical/virtual address translation

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Date:	Wed, 7 Apr 2010 15:28:21 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
	albert_herranz@...oo.es, chrisw@...s-sol.org,
	Ian.Campbell@...citrix.com, jeremy@...p.org, dwmw2@...radead.org,
	alex.williamson@...com
Subject: Re: [LKML] Re: [PATCH] swiotlb v0.6: seperation of
	physical/virtual address translation

> > Since the last posting I've:
> >  - Made the exported functions/variables have the 'swiotlb_bk' prefix instead
> >    of the 'do_[map|unmap]*' and 'io_tlb_*' combination.
> 
> Why can't we use more simpler names such as 'swiotlb_tbl_index'?

Much better. I was trying to come up with a name and the one I came up
with was 'bookkeeping', which I shortned to 'bk'. But 'tbl'
sounds better.

> Why do we need to add the prefix to static things like
> 'swiotlb_bk_list', 'swiotlb_bk_index', etc? Please let them alone.

Yup. Removed.
> > I had not addressed the question of removing the 'overflow' buffer. There are over
> > ~300 instances of the the DMA operations not being checked which plan on addressing
> > in a seperate set of patches that will slowly roll out the checks and then
> > finally the removal of the 'overflow' buffer.
> 
> Except for swiotlb, no IOMMU implementations has the mechanism of

I believe the GART one does it too. I think the overflow points to the
first page of the GART address and has logic to remind the user that danger
is immenient.

> overflow buffer. So drivers that don't check a DMA mapping error are
> broken anyway. Also the size of the overflow is 32K by default. We
> often see larger request than that. Even with the overflow mechanism,
> we see data corruption anyway.
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