Re: [Qemu-devel] [PATCH 1/2] hw/mips/jazz: create ESP device directly via qdev

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/06/2018 15:06, Mark Cave-Ayland wrote:
>>
>> Heh, those are disgusting indeed. :)  So I guess it would have to stay,
>> only MIPS can use the pure MemoryRegion-based approach.
> 
> The only option I can think of is inserting an AddressSpace between the
> esp/ledma device and the IOMMU AddressSpace which intercepts the DMA
> request (addr, len, direction).
> 
> I can then grab a reference to the device from the MemoryRegion opaque,
> perform the magic, and then manually invoke address_space_rw() on iommu_as.
> 
> Is there a hook somewhere in the memory API that could allow me to do this?

No, I don't think so.  Only MMIO regions intercept reads/writes, and
they only do it at 1/2/4/8 byte granularity.

>> Regarding pcnet, is CSR_BSWP really a no-op on PCI cards?  If not, an
>> option could be to move that handling to pcnet.c - making the ledma swap
>> unconditional and removing the do_bswap argument.  The disadvantage is
>> that SPARC would swap twice, and you'd have to keep the callback because
>> of s->dmaregs[3], but maybe it's still worthwhile.
> 
> Hmmm good question. If we can intercept the request above, that would be
> my preferred option as something tells it me it might be useful for
> other similar situations.

Yeah, it wouldn't be a great improvement, but there would be the benefit
of more accurate emulation.

Paolo