On 8 April 2014 21:27, Paolo Bonzini <pbonz...@redhat.com> wrote: > I agree, and in fact we should also use DEVICE_NATIVE_ENDIAN less, not more. > Unfortunately, forwarding accesses from one address space to another via > MMIO accessors requires DEVICE_NATIVE_ENDIAN, and that in turn requires > target-endianness ldl_p/stl_p.
I don't think this is correct. If we're purely forwarding then you can just use DEVICE_LITTLE_ENDIAN and ldl_le_p. There are three places in the sequence of calls from CPU to outer MMIO accessor to stl_le_p to memory_space_write that might insert bswaps: 1 before the call to the outer MMIO accessor we will bswap if the guest endianness is not LE (because we're calling an MMIO accessor that was marked DEVICE_LITTLE_ENDIAN) 2 in the stl_le_p we will bswap if the host endianness is not LE (because that's what stl_le_p means) 3 in memory_space_write when we read out of the buffer we do a ldl_q, which will bswap if the host endianness is not the target endianness (because we get the cpu-all.h version of ldl_q, which does a target-endian load) So: host = guest = LE: no swapping host = LE, guest = BE: swap 1 and 3 active host = BE, guest = LE: swap 2 and 3 active host = guest = BE: swap 1 and 2 active In all cases we do an even number of swaps and the whole thing cancels out :-) You can use DEVICE_BIG_ENDIAN and stl_be_p if you like, for equivalent effect. I'm pretty sure this wasn't an intentional design property, though... thanks -- PMM
