linux-kernel - Re: [PATCH RFC] virtio-pci: flexible configuration layout

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Message-ID: <20111103075929.7084a9b8@jbarnes-desktop>
Date:	Thu, 3 Nov 2011 07:59:29 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Sasha Levin <levinsasha928@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	Amit Shah <amit.shah@...hat.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Krishna Kumar <krkumar2@...ibm.com>,
	Pawel Moll <pawel.moll@....com>,
	Wang Sheng-Hui <shhuiw@...il.com>,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org
Subject: Re: [PATCH RFC] virtio-pci: flexible configuration layout

On Thu, 3 Nov 2011 01:31:11 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> Add a flexible mechanism to specify virtio configuration layout, using
> pci vendor-specific capability.  A separate capability is used for each
> of common, device specific and data-path accesses.
> 
> Warning: compiled only.
> This patch also needs to be split up, pci_iomap changes
> also need arch updates for non-x86.
> 
> We also will need to update the spec.
> 
> See the first chunk for layout documentation.
> 
> Posting here for early feedback.
> 
> In particular:
> 
> Do we need to require offset to be aligned?
> Does iowrite16 work with unaligned accesses on all architectures?
> Does using ioread/write as we do add overhead as compared to
> plain PIO accesses?
> 
> Jesse - are you OK with the pci_iomap_range API proposed here
> (see last chunks)?
> I noticed lots of architectures duplicate the implementation
> of pci_iomap - makes sense to clean that up?

Probably makes sense to have a weak version at least for arches that
just do the same thing.  But some arches really do need separate
versions because they wrap read/write as well...

Given the arch constraints, it's probably not possible to get rid of
the min/max args in favor of a simple offset/len pair like we have for
ioremap.  But if we could that would be even better.

-- 
Jesse Barnes, Intel Open Source Technology Center

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