[PATCH] drm: remove immutable flag from suggested X/Y connector properties

Michael Thayer michael.thayer at oracle.com
Wed Dec 21 14:30:04 UTC 2016

21.12.2016 10:05, Daniel Vetter wrote:
> On Tue, Dec 20, 2016 at 11:38:52AM +0100, Michael Thayer wrote:
>> The suggested X and Y connector properties are intended as a way for drivers
>> for virtual machine GPUs to provide information about the layout of the
>> host system windows (or whatever) corresponding to given guest connectors.
>> The intention is for the guest system to lay out screens in the virtual
>> desktop in a way which reflects the host layout.  Sometimes though the guest
>> system chooses not to follow those hints, usually due to user requests.  In
>> this case it is useful to be able to pass information back about the actual
>> layout chosen.
>> The immediate use case for this is host-to-guest pointer input mapping.
>> Qemu, VirtualBox and VMWare currently handle this by providing an emulated
>> graphics tablet device to the guest.  libinput defaults, as did X.Org before
>> it used libinput, to mapping the position information reported by the device
>> to the smallest rectangle enclosing the screen layout.  Knowing that layout
>> lets the hypervisor send the right position information through the input
>> device.
>> Signed-off-by: Michael Thayer <michael.thayer at oracle.com>
>> ---
>> Follow-up to thread "Passing multi-screen layout to KMS driver".  In that
>> thread, Gerd suggested an alternative way of solving the use case, namely
>> emulating one input device per virtual screen, touchscreen-style.  My reasons
>> for prefering this approach is that it is relatively uninvasive, and closer
>> to the way things are done now without (in my opinion) being ugly; and that
>> automatic touchscreen input to screen mapping is still not a solved problem.
>> I think that both are valid though.
>> Both approaches require changes to the hypervisor and virtual hardware, and
>> to user-space consumers which would use the interface.  I have checked the
>> mutter source and believe that the change required to support the interface
>> as implemented here would be minimal and intend to submit a patch if this
>> change is accepted.  I think that the virtual hardware changes are likely to
>> be less invasive with this approach than with the other.  This change will
>> though also require small drm driver changes once the virtual hardware has
>> been adjusted; currently to the qxl driver and to the out-of-tree vboxvideo
>> driver.  It would certainly be nice to have in virtio-gpu.
> Makes sense I think, but for merging we need:
> - some driver to implement

This is where it starts getting tricky.  vboxvideo is out of tree.  In 
theory I could look at getting it merged, but that needs time I am 
rather short of (I am the only person maintaining that driver and it is 
just one of my responsibilities; and there are some bits there that are 
probably too ugly to merge as is).  I don't think I am really the person 
to be doing this for qxl/virtio-gpu as that required adding the support 
to qemu too.  I think that they really should have it, but I would 
rather not be the one adding it.  So would our out-of-tree driver be 
good enough?

> - some userspace to take advantage of it

As I wrote, mutter would be the first candidate.

> - and some proper kernel-doc, we're deprecating that horrible property
>   table that no one human can maintain. Latest upstream has lots of
>   examples of what I have in mind.

I can take a look at that.

> Also if we make this mutable would be good to switch the entire
> scaffolding over to the atomic way of doing things, i.e. put the property
> value as a decoded thing into drm_connector_state and wire up all the
> handling. Means you need an atomic driver as demonstration vehicle, but
> I'd say you want that anyway ;-)

Currently vboxvideo is keeping close to ast as I have time to follow it. 
  Switching to atomic as long as ast is not switched likely means more 
new bugs introduced than I would like to have time to fix, plus 
maintaining two versions of vboxvideo, one for pre-atomic kernels and 
one for post.  At the moment we support 3.11 to 4.10 with a manageable 
minimum of conditional compilation.  So does "would be good" mean what 
it says, or is it meant slightly more strongly?

Thanks and regards,


> -Daniel
>> Regards
>> Michael
>>  Documentation/gpu/kms-properties.csv | 4 ++--
>>  drivers/gpu/drm/drm_connector.c      | 4 ++--
>>  2 files changed, 4 insertions(+), 4 deletions(-)
>> diff --git a/Documentation/gpu/kms-properties.csv b/Documentation/gpu/kms-properties.csv
>> index 981873a..825238e 100644
>> --- a/Documentation/gpu/kms-properties.csv
>> +++ b/Documentation/gpu/kms-properties.csv
>> @@ -20,8 +20,8 @@ Owner Module/Drivers,Group,Property Name,Type,Property Values,Object attached,De
>>  ,,“overscan”,RANGE,"Min=0, Max=100",Connector,TBD
>>  ,,“saturation”,RANGE,"Min=0, Max=100",Connector,TBD
>>  ,,“hue”,RANGE,"Min=0, Max=100",Connector,TBD
>> -,Virtual GPU,“suggested X”,RANGE,"Min=0, Max=0xffffffff",Connector,property to suggest an X offset for a connector
>> -,,“suggested Y”,RANGE,"Min=0, Max=0xffffffff",Connector,property to suggest an Y offset for a connector
>> +,Virtual GPU,“suggested X”,RANGE,"Min=0, Max=0xffffffff",Connector,"property to suggest an X offset for a connector to help match positions of host windows and guest screens; can be set by the driver for the host or user-space for the guest"
>> +,,“suggested Y”,RANGE,"Min=0, Max=0xffffffff",Connector,"property to suggest an Y offset for a connector to help match positions of host windows and guest screens; can be set by the driver for the host or user--space for the guest"
>>  ,Optional,"""aspect ratio""",ENUM,"{ ""None"", ""4:3"", ""16:9"" }",Connector,TDB
>>  i915,Generic,"""Broadcast RGB""",ENUM,"{ ""Automatic"", ""Full"", ""Limited 16:235"" }",Connector,"When this property is set to Limited 16:235 and CTM is set, the hardware will be programmed with the result of the multiplication of CTM by the limited range matrix to ensure the pixels normaly in the range 0..1.0 are remapped to the range 16/255..235/255."
>>  ,,“audio”,ENUM,"{ ""force-dvi"", ""off"", ""auto"", ""on"" }",Connector,TBD
>> diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
>> index 5a45262..ebb3cee 100644
>> --- a/drivers/gpu/drm/drm_connector.c
>> +++ b/drivers/gpu/drm/drm_connector.c
>> @@ -876,10 +876,10 @@ int drm_mode_create_suggested_offset_properties(struct drm_device *dev)
>>  		return 0;
>>  	dev->mode_config.suggested_x_property =
>> -		drm_property_create_range(dev, DRM_MODE_PROP_IMMUTABLE, "suggested X", 0, 0xffffffff);
>> +		drm_property_create_range(dev, 0, "suggested X", 0, 0xffffffff);
>>  	dev->mode_config.suggested_y_property =
>> -		drm_property_create_range(dev, DRM_MODE_PROP_IMMUTABLE, "suggested Y", 0, 0xffffffff);
>> +		drm_property_create_range(dev, 0, "suggested Y", 0, 0xffffffff);
>>  	if (dev->mode_config.suggested_x_property == NULL ||
>>  	    dev->mode_config.suggested_y_property == NULL)
>> --
>> 2.9.3
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Michael Thayer | VirtualBox engineer
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