Re: [Qemu-ppc] [Qemu-devel] [PATCH 2/3] mac_newworld: enable access to EDID data for the VGA device

[Mark Cave-Ayland]

On 12/12/2018 08:32, Gerd Hoffmann wrote:

> On Fri, Dec 07, 2018 at 04:08:05PM +0000, Mark Cave-Ayland wrote:
>> This is in preparation for some upcoming QEMU NDRV driver changes that pass
>> display information from the host to the guest.
> 
>> -    pci_vga_init(pci_bus);
>> +    dev = qdev_create(BUS(pci_bus), "VGA");
>> +    qdev_prop_set_int32(dev, "addr", -1);
>> +    qdev_prop_set_bit(dev, "edid", true);
>> +    qdev_init_nofail(dev);
> 
> Hmm.  IMO you should not overwrite the device defaults here.
> 
> edid is off by default only because it is new and I'm conservative.
> I want a release (or two) with it being available for user testing.
> If no issues pop up flip it to default on.

Oh, okay. I already have some unreleased guest code that makes use of this, so 
my
questions would be: how can EDID be enabled from the command line for in-built 
VGA
devices, and how do I detect whether EDID support is present from the guest?
Otherwise a guest driver that assumes it is always present and tries to read 
from
that area of memory will crash.


ATB,

Mark.