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. -ilia _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
