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Re: [Qemu-devel] [PATCH] qxl: use correct rom size for revision < 4


From: Yonit Halperin
Subject: Re: [Qemu-devel] [PATCH] qxl: use correct rom size for revision < 4
Date: Thu, 13 Dec 2012 09:30:47 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0

On 12/13/2012 05:40 AM, Alon Levy wrote:
On 12/06/12 16:41, Alon Levy wrote:
RHBZ 869981

Before this patch revision < 4 (4 is the default) would result in a
wrong
qxl_rom size of 16384 instead of 8192 when building with
spice-protocol-0.12, due to the addition of fields in
the rom for client capabilities and monitors config that were added
between spice-protocol 0.10 and 0.12.

The solution is a bit involved, since I decided not to change
QXLRom
which is defined externally in spice-protocol. Instead for revision
< 4
we allocate 72 bytes for the QXLRom on the qxl_rom bar (bytes
[0,71])
and make sure no fields out of that range are accessed, via
checking of
the revision and nop-ing.

Ok, I see we tackle two issues here.

Number one is qxl accessing the new fields with revision being < 4.
That needs fixing indeed.  But separate patch please.

Will do.


Number two is breaking migration due to the rom size change.  Can't
we
just get the rom below 8k again instead?  I think we can throw away a
whole bunch of modes.  Each mode is four times in the list, for
orientation = { 0, 1, 2, 3 }.  orientation is never ever used
anywhere,
looks like historic leftover or something planned which was never
actually implemented.

So keeping orientation = 0 only and kick out everything else should
give
us plenty of room ...

That is indeed a better solution, but it does change functionality. I think it 
is correct but I'd like to get some other opinions - Uri, Arnon, Yonit, Soren - 
any problems with dropping these?

Orientation is used in the Windows Display driver. It is used to set
dmDisplayOrientation in DEVMODEW structure (http://msdn.microsoft.com/en-us/library/windows/hardware/ff552837(v=vs.85).aspx). So, I'm not sure we can just drop it. Moreover, we need at least 2 of the orientations, one for AxB resolution and the other for BxA.

cheers,
   Gerd







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