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Re: [Qemu-devel] [PATCH 2/3] mac_newworld: enable access to EDID data fo
Re: [Qemu-devel] [PATCH 2/3] mac_newworld: enable access to EDID data for the VGA device
Tue, 18 Dec 2018 06:31:28 -0500
> On 12/12/2018 13:38, Gerd Hoffmann wrote:
>> On Wed, Dec 12, 2018 at 08:54:37AM +0000, Mark Cave-Ayland wrote:
>>> 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
>>>>> 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
>> "-global VGA.edid=on" should do.
>>> and how do I detect whether EDID support is present from the guest?
>> Check whenever the header is present. The edid blob has a fixed 8 byte
>> header (00 FF FF FF FF FF FF 00). The linux kernel driver is lazy and
>> checks the first two bytes only.
>>> Otherwise a guest driver that assumes it is always present and tries
>>> to read from that area of memory will crash.
>> Oh, reading should work no matter what. You just don't find valid edid
>> data there if it is turned off.
> Thanks for the info. My current use case for this is passing a set of
> possible guest
> display resolutions from the host to the guest driver, rather than using an
> hard-coded list. I guess that over time QEMU could become "smarter" about
> the list of supported resolutions depending upon the capabilities of the host?
Would could have both a hard-coded list and resolutions supported by the host.
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