On Thu, Dec 3, 2015 at 11:10 AM, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > 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 ;-) Sure, but it's identical to Jaakko's proposal from what I can (quickly) tell. And it's an example of someone taking an interface like that and writing a proprietary driver on top. -ilia _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/dri-devel
