On 03/12/15 18:38, Ilia Mirkin wrote:
On Thu, Dec 3, 2015 at 11:10 AM, Laurent Pinchart laurent.pinchart@ideasonboard.com 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
You are right Ilia, this is indeed what Jaakko and I had in mind, but they did not re-use the fuse/cuse framework to do the serialization of the ioctls.
Not sure what we can do against allowing proprietary drivers to use this feature though :s To be fair, nothing prevents any vendor to do this shim themselves and nvidia definitely did it, and directly called their closed-source driver.
Any proposition on how to handle this case? I guess we could limit that to screens only, no rendering. That would block any serious GPU manufacturer from using this code even if any sane person would never write a driver in the userspace...