[vbox-dev] Have any non-Linux developers looked at the vboxvideo drm/kms driver?

Michael Thayer michael.thayer at oracle.com
Wed Feb 8 13:49:41 GMT 2017

08.02.2017 14:44, Jan Petrouš wrote:
> On 8 February 2017 at 14:35, Michael Thayer <michael.thayer at oracle.com
> <mailto:michael.thayer at oracle.com>> wrote:
>> 08.02.2017 14:14, Jan Petrouš wrote:
>> [...]
>>> On 8 February 2017 at 13:45, Michael Thayer
> <michael.thayer at oracle.com <mailto:michael.thayer at oracle.com>
>>> <mailto:michael.thayer at oracle.com
> <mailto:michael.thayer at oracle.com>>> wrote:
>> [...]
>>>> I'm afraid I will have to ask for a bit of clarification there.  My
>>> understanding of a frame buffer is an area of (usually video) memory
>>> representing the image shown on a screen.  You can have more or less as
>>> many of those as will fit into video memory and flip between them.  You
>>> can also have up to 32 virtual screens (the hardware supports 64).
>> [...]
>>> Ok, I might describe it vague, so yes - I need more virtual screens each
>>> of them with support of framebuffer. So if I enable, for ex. 4 screens
>>> (or monitors?), then I expect to have also /dev/fb0 - /dev/fb3 devices,
>>> writing to which will be displayed on appropriate virtual screen.
>> [...]
>> That is less vague now - you mean Linux frame buffer devices.
> Currently no plans for that, but our driver code is probably not the
> right place to do it anyway: we use the generic fbdev-on-KMS wrapper in
> the Linux kernel, so unless we are using it wrongly in some way (and I
> just checked that my two-screen host also only provides one fbdev
> device) you would need to talk to the kernel drm maintainers about it[1].
> Yep. That's the reason I'm asking about. As last time I tried to play
> with it was exactly in that state = only one /dev/fb on multiscreen
> enabled VB config.
> I also checked the driver source and the reason is (or better was in
> time I looked inside) evident - only single FB node is supported there.
Feel free to provide a patch to fix it then if you think this is 
something we are doing wrong.  It doesn't necessarily have to be a fully 
working patch (I would probably change it anyway when I apply it) as 
long as it clearly shows what needs changing.  No promises of course 
that I would make the change, as it is not the most pressing feature, 
but the chances are higher than if you don't (and if it is on the 
mailing list the knowledge will keep fresh longer).

> Anyway, thanks for info. I don't need it right now, so it was more
> matter of interest then a real request
> (even I still see there nice way of enhancement of VB usage).
Michael Thayer | VirtualBox engineer
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