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Re: [Qemu-devel] [PULL 35/35] ppc: Include vga cirrus card into the comp

From: Mark Cave-Ayland
Subject: Re: [Qemu-devel] [PULL 35/35] ppc: Include vga cirrus card into the compiling process
Date: Wed, 4 Jul 2018 06:56:13 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 04/07/18 06:33, Sebastian Bauer wrote:

Am 2018-07-04 06:50, schrieb Mark Cave-Ayland:
Either to give up the vga cirrus preference or to apply the same as was done with the spapr machine. I would prefer the first variant but it would also cause some differences on other machines.

I understand that the decision was taken to add VGA cirrus to the PPC
build and therefore accept the default VGA device change, however your
the commit message only mentions spapr and not all the other PPC
machines whose defaults are also potentially affected:

$ ./qemu-system-ppc -M ?
Supported machines are:
40p                  IBM RS/6000 7020 (40p)
bamboo               bamboo
g3beige              Heathrow based PowerMAC (default)
mac99                Mac99 based PowerMAC
mpc8544ds            mpc8544ds
none                 empty machine
ppce500              generic paravirt e500 platform
prep                 PowerPC PREP platform
ref405ep             ref405ep
sam460ex             aCube Sam460ex
taihu                taihu
virtex-ml507         Xilinx Virtex ML507 reference design

I'm not able to personally validate all of these, but a quick check
shows that at least both PReP machines (-M prep and -M 40p) are also
broken by this patch which tells me it hasn't had much testing.

David, do you know what the defaults are for the other PPC machines in
order for Sebastian to test and send a follow-up patch?

I don't know much how to validate these machines (I did a 'make check' but it does not show up any problems) and what impact these change has. But I suggested in the note section (which is not the commit message) that some of the machines properly behave different now (OTOH CirrusGD is a vga card nonetheless, I would have expected that at least the Mac can deal with that card). This can either be fixed by following the 'spapr' approach (as it explicitly forbids this card as the primary display and was therefore visible immediately) or by generally rethinking whether CirrusGD really should be the preferred card over std vga (after all it is considered as obsolete so why should it be preferred?). I think it would be nice if a consensus can be found about the "correct approach" way to fix it. I personally think that adding more exceptions is not the right way :)

Right, but as the patch submitter it's your responsibility to ensure that your patch doesn't break other people's machines and/or follow up with the appropriate patches. If you're not willing to do that then we should revert the patch in its current form until a better way forward has been found.

Last but not least, all of the targets should still work as before if you use -vga std option.

Except that -vga std has been the default for these machines for a long time, and it's going to be me that will get a large majority of the complaints if this behaviour changes.



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