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Re: [Qemu-devel] [PATCH 0/3] vga: add endianness switching support
From: |
Benjamin Herrenschmidt |
Subject: |
Re: [Qemu-devel] [PATCH 0/3] vga: add endianness switching support |
Date: |
Wed, 24 Sep 2014 06:24:33 +1000 |
On Tue, 2014-09-23 at 14:30 +0200, Gerd Hoffmann wrote:
> Hi,
(Adding Mike)
> Series applies on top of the vga patches posted yesterday.
> It adds a mmio register to the pci stdvga cards allowing
> to switch framebuffer endiannness. Ben's patches 1+2 prepare
> for runtime-swicthable endianness and patch #3 actually
> implements the new register. It has been placed in a new
> range to avoid conflicts in case the bochs dispi interface
> will be extended in the future. The separate range also
> makes it easier to turn off on old machine types.
Thanks. I'll try to produce patches for offb and bochsdrmfb to
adjust endianness & test some time this week or next week.
Now the remaining point of contention is the "auto switch"
functionality which, sadly, is needed for existing LE guests to work
properly.
I understand the reticence, on the other hand, our "pseries" machine is
really a paravirtualized environment where qemu implements the
hypervisor hcall interface, so in that context, it does make some sense
that the "hypervisor" affects some HW configuration/state on endian
switch (which is such an hcall).
The problem is how to do that in a reasonably clean way from an
implementation perspective.
The patch at
https://github.com/ozbenh/qemu/commit/778c92cebcd12fdafd2050dc4d7ca2521c462e46
is one attempt to do it, for whatever it's worth, but I'm open to alternatives.
Cheers,
Ben.