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

On Thu, 3 Nov 2011 01:31:11 +0200
"Michael S. Tsirkin" [off-list ref] 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