Re: [PATCH v4 0/4] virtio: Clean up scatterlists and use the DMA API

[Benjamin Herrenschmidt <benh@au1.ibm.com>]

On Tue, 2014-09-02 at 17:32 -0700, Andy Lutomirski wrote:
> 
> I agree *except* that implementing it will be a real PITA and (I
> think) can't be done without changing code in arch/.  My patches plus
> an ifdef powerpc will be functionally equivalent, just uglier.

So for powerpc, it's a 2 liner inside virtio-pci, but yes, it might be
more of a problem for s390, I'm not too sure what they do in that area.

> Bigger quirk: on a standard s390 virtio guest configuration,
> dma_map_single etc will fail to link. 

Yuck

>  I tried this in v1 of these
> patches.  So we can poke at the archdata all day, but we can't build a
> kernel like that :(

I would like the s390 people to chime in here, it still looks like the
best way to go if they can fix things on their side :-)

> So until the dma_ops pointer move into struct device and
> CONFIG_HAS_DMA becomes mandatory (or mandatory enough that virtio can
> depend on it), I don't think we can do it this way.

I see, it's a bummer because it would be a lot cleaner.

> I'll send a v5 that is the same as v4 except with physical addressing
> hardcoded in for powerpc.

Thanks. That will do for now, but ideally we want to make it a function
of some flag from the implementation, so let's see what Rusty has to
say.

Cheers,
Ben.