On Thu, Mar 30, 2017 at 08:44:25AM +0200, David Herrmann wrote: > Hey > > On Wed, Mar 29, 2017 at 11:42 PM, Laurent Pinchart > <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > > Hi David, > > > > On Wednesday 29 Mar 2017 14:51:48 David Herrmann wrote: > >> On Wed, Mar 29, 2017 at 2:20 PM, Laurent Pinchart wrote: > >> > On Wednesday 29 Mar 2017 11:58:23 Tomi Valkeinen wrote: > >> >> On 29/03/17 11:22, Laurent Pinchart wrote: > >> >>> On Tuesday 28 Mar 2017 16:07:52 Tomi Valkeinen wrote: > >> >>>> From: Hemant Hariyani <hemanthariyani@xxxxxx> > >> >>>> > >> >>>> Add support for render nodes in omap driver and allow required > >> >>>> ioctls to be accessible via render nodes. > >> >>> > >> >>> But the OMAP DSS doesn't perform rendering... This seems an abuse of > >> >>> render nodes, I think the API should instead be implemented by the GPU > >> >>> driver. > >> >> > >> >> I agree that the GPU use case described in the patch sounds a bit odd. > >> >> Why not allocate from the GPU driver instead. But here a particular > >> >> issue is that to get TILER buffers we need to ask them from the omapdrm. > >> >> Probably TILER should not be part of omapdrm, but then, where should it > >> >> be... > >> >> > >> >> We also have writeback in DSS, which can function as a memory to memory > >> >> or capture device. That's not supported in the mainline, but we have > >> >> support in the TI kernel. > >> >> > >> >> And how about a case where you have the privileged process as KMS > >> >> master, and another process wants to draw to a buffer with the CPU, and > >> >> then give the buffer to the privileged process for displaying. > >> >> > >> >> So, yes, DSS is not a renderer (well, WB is kind of rendering), but > >> >> isn't it a valid use case to allocate a buffer from omapdrm? > >> > > >> > It could be a valid use case, but it's still an API abuse. It starts > >> > sounding like a DRM core issue to me. The DRIVER_RENDER flag is not > >> > documented, so its exact meaning isn't defined. I thought it was supposed > >> > to flag the device as a renderer (GPU). > >> > > >> > commit 1793126fcebd7c18834f95d43b55e387a8803aa8 > >> > Author: David Herrmann <dh.herrmann@xxxxxxxxx> > >> > Date: Sun Aug 25 18:29:00 2013 +0200 > >> > > >> > drm: implement experimental render nodes > >> > > >> > Render nodes provide an API for userspace to use non-privileged GPU > >> > commands without any running DRM-Master. It is useful for offscreen > >> > rendering, GPGPU clients, and normal render clients which do not > >> > perform > >> > modesetting. > >> > > >> > [...] > >> > > >> > You instead use the flag as a way to enable unprivileged clients to > >> > allocate buffers. If that's what the flag should mean, I wonder if there > >> > would be a use case for *not* setting it. > >> > >> Correct. You can (and should) enable all your sandboxed commands on > >> render nodes. That is, if a command only affects the issuing client, > >> then it is safe for render-nodes. If two clients have a file-context > >> opened on the render node, they should be unable to affect each other > >> (minus accounting, resource allocation, etc.). > >> > >> The name is historic (I did not come up with it either, but failed at > >> renaming it..). The DRIVER_RENDER flag only controls whether the > >> render-node is actually instantiated. I will not object doing that > >> unconditionally. It will create some useless nodes for legacy drivers, > >> but we should not care. > > > > Couldn't we achieve the same effect without render nodes, by allowing GEM > > object allocation on the main DRM node by unauthenticated clients ? > > Using a different inode makes sure you can sand-box the node. That is, > you can now easily mknod a render node in containers and sandboxes > without risk of exposing any other APIs. > > I guess you could achieve something similar by careful selection of > which privs to pass to the container. But we preferred a clean cut > back then. btw would be lovely if you folks could review the render node docs and make sure they reflect all the nuances discussed here properly: https://dri.freedesktop.org/docs/drm/gpu/drm-uapi.html#render-nodes And if not, please send a patch. Thanks, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
