Hi Ilia, On Thursday 03 December 2015 11:03:28 Ilia Mirkin wrote: > On Thu, Dec 3, 2015 at 10:53 AM, Laurent Pinchart wrote: > > On Thursday 03 December 2015 10:42:50 Ilia Mirkin wrote: > >> On Thu, Dec 3, 2015 at 10:34 AM, Laurent Pinchart wrote: > >>> On Thursday 03 December 2015 14:42:51 Hannikainen, Jaakko wrote: > >>>> Hello, > >>>> > >>>> We're developing Miracast (HDMI over Wireless connections). The > >>>> current progress is that it 'works' in the userspace but doesn't have > >>>> any integration with X/Wayland and can only mirror the current desktop > >>>> using gstreamer. > >>>> > >>>> We're looking into extending the implementation so that we would be > >>>> able to use the remote screens just as any other connected screen, but > >>>> we're not quite sure where we should implement it. > >>>> > >>>> The DRM interface seems like the perfect fit since we wouldn't need to > >>>> patch every compositor. > >>>> > >>>> Right now, gstreamer is the equivalent of the crtc/encoder, in the DRM > >>>> model. Screens / crtcs are discovered using a WiFi's p2p protocol > >>>> which means that screens should be hotpluggable. Since we cannot > >>>> change the number of crtcs of a driver on the fly, we propose adding > >>>> and removing gpus with one crtc attached and no rendering > >>>> capabilities. > >>>> > >>>> Compositors and X currently use udev to list gpus and get run-time > >>>> events for gpu hot-plugging (see the work from Dave Airlie for USB > >>>> GPUs, using the modesetting X driver). We did not find a way to tell > >>>> udev that we have a new device and it seems like the only way to get > >>>> it to pick up our driver is from a uevent which can only be generated > >>>> from the kernel. > >>>> > >>>> Since we have so many userspace components, it doesn't make sense to > >>>> implement the entire driver in the kernel. > >>>> > >>>> We would thus need to have a communication from the kernel space to > >>>> the userspace at least to send the flip commands to the fake crtc. > >>>> Since we need this, why not implement everything in the userspace and > >>>> just redirect the ioctls to the userspace driver? > >>>> > >>>> This is exactly what fuse / cuse [1] does, with the minor catch that > >>>> it creates devices in /sys/class/cuse instead of drm. This prevents > >>>> the wayland compositors and X to pick it up as a normal drm driver... > >>>> > >>>> We would thus need to have the drm subsystem create the device nodes > >>>> for us when the userspace needs to create a new gpu. We could create a > >>>> node named /dev/dri/cuse_card that, when opened, would allocate a node > >>>> (/dev/dri/cardX) and would use cuse/fuse to redirect the ioctls to the > >>>> process who opened /dev/dri/cuse_card. > >>>> > >>>> The process would then be responsible for decoding the ioctl and > >>>> implementing the drm API. > >>>> > >>>> Since this is a major change which would allow proprietary drivers to > >>>> be implemented in the userspace and since we may have missed something > >>>> obvious, we would like to start a discussion on this. What are your > >>>> thoughts? > >>> > >>> As you raise the issue, how would you prevent proprietary userspace > >>> drivers to be implemented ? Anything that would allow vendors to > >>> destroy the Linux graphics ecosystem would receive a big nack from me. > >> > >> AFAIK the displaylink people already have precisely such a driver -- a > >> (open-source) kernel module that allows their (closed-source) > >> userspace blob to present a drm node to pass through modesetting/etc > >> ioctl's. > > > > Are you talking about the drivers/gpu/drm/udl/ driver ? I might be wrong > > but I'm not aware of that kernel driver requiring a closed-source > > userspace blob. > Nope. That driver only works for their USB2 parts. This is what I mean: > > https://github.com/DisplayLink/evdi > http://support.displaylink.com/knowledgebase/articles/679060 > http://support.displaylink.com/knowledgebase/articles/615714#ubuntu Right. That's out-of-tree, people are free to screw up on their own there ;-) -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
