Re: Possible regression with VGA and resolutions in Windows 10?

[Aaron Lauterer <a.lauterer@proxmox.com>]

On 7/24/20 11:41 AM, Gerd Hoffmann wrote:
> On Thu, Jul 23, 2020 at 04:24:06PM +0200, Aaron Lauterer wrote:
>> Hi all,
>>
>> I think we have a regression introduced in commit 0221d73ce6.
>>
>> Once I start a Windows 10 VM (build 18363) with `-device VGA` I have only the following resolutions to choose from instead of the much longer list:
>>
>> 1920x1080
>> 1024x768
>> 800x600
> 
> That is probably vgabios gaining edid support.
> 
> The list should be longer though, the qemu edid block has more
> resolutions included.  The qemu-edid tool is a command line
> interface to the edid generator, for testing purposes.
> 
> Try "qemu-edid | edid-decode" to see the decoded edid data.
> 
> Linux guests have the raw edid block in sysfs, see
> /sys/class/drm/card0/card0-Virtual-1/edid.
> 
>>    -device 'VGA,id=vga,vgamem_mb=32,bus=pci.0,addr=0x2' \
> 
> Try adding "xres=<width>,yres=<height>" of you want a specific
> display resolution.
> 
> Try adding "edid=off" to return to previous behavior.

I did try that initially but it seemingly was ignored by Windows.

But I took another look at it and I was able to observe the following behavior with Win10:

Boot it first with edid enabled (by default) and I see only the short list of possible resolutions (I forgot 640x480, which is only shown in the Display Adapter Properties -> List all modes).

Boot it with edid=off and nothing changes, still the short list.
Uninstall the `Microsoft Basic Display Adapter` in Device Manager and reboot the VM. Now it recognizes all resolutions again.

The behavior is similar when setting a custom resolution with the xres and yres parameters. Setting it the first time works fine and it is shown along with the short list. Setting it to something different on the next boot will not be recognized unless the display adapter is uninstalled and the VM rebooted.

The same applies when changing from edid=off to edid=on. Only after uninstalling the display driver and a reboot will it change from showing the long list of resolution to the mentioned short one.


Knowing that uninstalling the display driver after setting edid=off will help is good enough for now.

Thanks for pointing that out again and nudging me in the right direction.

All the best,
Aaron


> 
> HTH & take care,
>    Gerd
> 
> 
>