Re: [RFC PATCH 3/3] hw/openrisc: Add the OpenRISC virtual machine

[Stafford Horne <shorne@gmail.com>]

On Tue, Jun 07, 2022 at 11:43:08AM +0100, Peter Maydell wrote:
> So I don't have a strong view on whether these devices should
> be DEVICE_NATIVE_ENDIAN or DEVICE_LITTLE_ENDIAN (except that
> my impression is that a DEVICE_LITTLE_ENDIAN device on a
> big-endian system is a bit weird, because it means the guest
> has to byteswap everything. You see that with PCI devices because
> the PCI spec mandates LE, but not often elsewhere).
> 
> If there's an official-ish spec for how goldfish devices are
> supposed to behave (does anybody have a pointer to one?) and it says
> "always little-endian" then that would probably suggest that fixing
> m68k would be nice if we can.

I think there are some conflicting thoughts on this.

In Geert's he mentioned:

  Using Goldfish devices as little-endian devices should be fine.

In Arnd's mail he mentions:

  https://lore.kernel.org/lkml/CAK8P3a1oN8NrUjkh2X8jHQbyz42Xo6GSa=5n0gD6vQcXRjmq1Q@mail.gmail.com/#t

  ... the device was clearly defined as having little-endian
  registers,

Based on that I was thinking that switching to DEVICE_LITTLE_ENDIAN would make
sense.

However, in a followup mail from Laurent we see:

  https://lore.kernel.org/lkml/cb884368-0226-e913-80d2-62d2b7b2e761@vivier.eu/

  The reference document[1] doesn't define the endianness of goldfish.

  [1] https://android.googlesource.com/platform/external/qemu/+/master/docs/GOLDFISH-VIRTUAL-HARDWARE.TXT


The documentation does not clearly specify it.  So maybe maybe or1k should just
be updated on the linux side and add gf_ioread32/gf_iowrite32 big-endian
accessors.

-Stafford