Re: [Qemu-devel] [PATCH 00/13] iommu series

[Anthony Liguori]

On 06/19/2012 01:39 AM, Benjamin Herrenschmidt wrote:
> This is a rebase of the iommu series and the barrier patch together
> on top of current qemu.
>
> As for our discussions about doing things with Memory Regions etc
> I eventually came to the conclusion that we should just apply this
> first :-)
>
> My reasons (other than it makes my life much easier which it does)
> are that:

This series sucks pretty bad.  I don't think it can be a lot better though 
without major rearchitecting so I'm in favor of applying this now and dealing 
with the fall-out later.

I'll respond in detail where all of the problems are.  I don't have easy 
solutions to offer though.

Regards,

Anthony Liguori

>   - We already have PCI DMA accessors, so devices using those
> will be unaffected by further changes
>
>   - The few devices that are modified in this series to use the
> DMA accessors directly are ... few, and need to do it essentially
> because they either deal with multiple bus types (AHCI, EHCI,...)
> or because they are in a separate layer (bdev). Fixing them to
> use some other interfaces would be easy (they are few)) and might
> be unnecessary as well as we might want (or can) easily keep an
> object of type "DMAContext" to represent the DMA capabilities of a
> device as the head of the chain of MemoryRegions in a future
> more flexible design.
>
>   - It provides a good spot to stick our memory barrier
>
>   - It gives us something working now for 1.2, I know that at least
> freescale powerpc and a number of ARM folks are waiting for it.
>
> Cheers,
> Ben.