On Thursday 03 December 2015 10:42:50 Ilia Mirkin wrote: > On Thu, Dec 3, 2015 at 10:34 AM, Laurent Pinchart > > <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > Hi Jaakko, > > > > 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. -- Regards, Laurent Pinchart _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
