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

[Arnd Bergmann]

On Tue, Jun 7, 2022 at 10:11 AM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> On Sun, Jun 5, 2022 at 9:32 AM Stafford Horne <shorne@gmail.com> wrote:
> > On Sun, Jun 05, 2022 at 10:58:14AM +0900, Stafford Horne wrote:
> >     It might be a good idea to revisit the qemu implementation and make
> >     sure that the extra byteswap is only inserted on m68k and not on
> >     other targets, but hopefully there are no new targets based on goldfish
> >     anymore and we don't need to care.
> >
> > So, it seems that in addition to my patch we would need something in m68k to
> > switch it back to 'native' (big) endian?
> >
> > Looking at the m68k kernel/qemu interface I see:
> >
> > Pre 5.19:
> >    (data) <-- kernel(readl / little) <-- m68k qemu (native / big) - RTC/PIC
> >    (data) <-- kernel(__raw_readl / big) <-- m68k qemu (native / big) - TTY
> >
> > 5.19:
> >    (data) <-- kernel(gf_ioread32 / big) <-- m68k qemu (native / big) - all
> >
> > The new fixes to add gf_ioread32/gf_iowrite32 fix this for goldfish and 
> > m68k.
> > This wouldn't have been an issue for little-endian platforms where 
> > readl/writel
> > were originally used.
> >
> > Why can't m68k switch to little-endian in qemu and the kernel?  The m68k 
> > virt
> > platform is not that old, 1 year? Are there a lot of users that this would 
> > be a big
> > problem?
> >
> > [1] 
> > https://lore.kernel.org/lkml/CAK8P3a1oN8NrUjkh2X8jHQbyz42Xo6GSa=5n0gD6vQcXRjmq1Q@mail.gmail.com/

Goldfish is a very old platform, as far as I know only the kernel port is new.
I don't know when qemu started shipping goldfish, but changing it now would
surely break compatibility with whatever OS the port was originally made for.

      Arnd