Re: [Qemu-devel] [RFC PATCH 01/13] Generic DMA memory access interface

[David Gibson]

On Wed, Jun 01, 2011 at 08:16:44AM -0700, Richard Henderson wrote:
> On 06/01/2011 07:29 AM, Avi Kivity wrote:
> > On 06/01/2011 05:01 PM, Richard Henderson wrote:
> >> >  +        err = dev->mmu->translate(dev, addr,&paddr,&plen, is_write);
> >>
> >> I see you didn't take my suggestion for using an opaque callback pointer.
> >> Really and truly, I won't be able to use this as-is for Alpha.
> >>
> > 
> > Rather than opaques, please pass the DMA engine itself and use 
> > container_of().
> 
> The dma engine object is currently sitting in the PCIBus structure.
> Which is private, and can't be extended by a host bridge implementation.
> 
> The entire code could be re-arranged, true, but please suggest something
> reasonable.
> 
> > We should be removing opaques, not adding them.
> 
> See my followup elsewhere.  Opaques *can* be cleaner than upcasting,
> particularly if there are too many hoops through which to jump.

So, in the meantime, I've also done a version of Eduard's earlier
patches, with added support for the PAPR hypervisor managed IOMMU.

I have also significantly reworked how the structure lookup works,
partly because in my case I'l looking at IOMMU translation for non-PCI
devices, but I think it may also address your concerns.  I'm still
using upcasts, but there are less steps from the device to the IOMMU
state.

I've been sick and haven't had a chance to merge my stuff with
Eduard's changes.  I'll post them anyway, as another discussion
point.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson