Original commit 8059add0478e29cb641936011a8fcc9ce9fd80be (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/gpu/drm/drm_ioctl.c?id=8059add0478e29cb641936011a8fcc9ce9fd80be) was added in 5.1 merge cycle and reverted by dbb92471674a48892f5e50779425e03388073ab9 (https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=dbb92471674a48892f5e50779425e03388073ab9) in 5.2. So radv is still broken in 5.1.
In 5.1.10: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-5.1.y&id=c2d2804b9939402f6ac9514d049e4469b6e1cb5d SteamVR works.