On Thu, Jan 5, 2023 at 10:48 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > On Thu, Jan 05, 2023 at 09:52:26PM +0900, Yi Xie wrote: > > > This doesn't sound like a good idea to me. Devices without render > > > capabilities should not fake it. > > > > > > User-space (e.g. wlroots) relies on "no render node" to enable > > > software rendering (Pixman instead of GL). > > > > We have virtgpu driver that exports a render node even when virgl is > > not supported. > > Mesa has special code path to enable software rendering on it: > > https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/src/egl/drivers/dri2/platform_device.c#L296 > > We can do the same for vkms to force software rendering. > > Yeah that is the old kmsro mesa issue, for every combination of kms and > gem device you need one to make this work. > > > On Thu, Jan 5, 2023 at 8:36 PM Daniel Vetter <daniel@xxxxxxxx> wrote: > > > > > > On Thu, Jan 05, 2023 at 02:23:25PM +0900, Yi Xie wrote: > > > > Some libraries including Mesa and virglrenderer require a render node to > > > > fully function. By adding a render node to vkms those libraries will > > > > work properly, supporting use cases like running crosvm with virgl GPU > > > > support via llvmpipe on a headless virtual machine. > > > > > > This is what vgem exists for. More or less at least ... I'm honestly not > > > really understanding what you're trying to fix here, it sounds a bit like > > > userspace being stupid. > > > -Daniel > > The problem with vgem is that it crashes llvmpipe while working with vkms. > > Looks like it's due to the same reason as described in this thread in Mesa: > > https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5830 > > I'm not finding any bug description in there and how/why something > crashes? The discussion is in the comment section under the first comment by Emil Velikov. It's folded by default (inside "6 replies" at the bottom). > > > Importing buffers allocated by vgem to vkms seems to be unexpected and > > causes the crash. If we create a render node on vkms then llvmpipe will use > > vkms to allocate buffers and it no longer crashes. > > Uh importing vgem into virtio might not work because those sometimes need > special buffers iirc. But importing vgem into vkms really should work, > there's no technical reason it cannot. If it doesn't, then the right fix > would be to fix that, not paper around it. The crash stack trace looks like this: https://gist.github.com/imxieyi/03053ae79cee2e614850fd41829e1da2 Even if we fix the crash issue with vgem, we still need to workaround quite a few places that has explicitly blocked vgem. A notable example is virglrenderer: https://gitlab.freedesktop.org/virgl/virglrenderer/-/blob/master/src/vrend_winsys_gbm.c#L121 Actually I have tried to force running virglrenderer on vgem and it didn't work. I didn't look into why it wasn't working but I guess that's the reason for blocking vgem in the first place. Virglrenderer works well on vkms with render node enabled though. > -Daniel > > > > > > > > > > > Signed-off-by: Yi Xie <yixie@xxxxxxxxxx> > > > > --- > > > > drivers/gpu/drm/vkms/vkms_drv.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c > > > > index 293dbca50c31..8eea5d4dece8 100644 > > > > --- a/drivers/gpu/drm/vkms/vkms_drv.c > > > > +++ b/drivers/gpu/drm/vkms/vkms_drv.c > > > > @@ -113,7 +113,7 @@ static void vkms_config_debugfs_init(struct drm_minor *minor) > > > > } > > > > > > > > static const struct drm_driver vkms_driver = { > > > > - .driver_features = DRIVER_MODESET | DRIVER_ATOMIC | DRIVER_GEM, > > > > + .driver_features = DRIVER_MODESET | DRIVER_ATOMIC | DRIVER_GEM | DRIVER_RENDER, > > > > .release = vkms_release, > > > > .fops = &vkms_driver_fops, > > > > DRM_GEM_SHMEM_DRIVER_OPS, > > > > -- > > > > 2.39.0.314.g84b9a713c41-goog > > > > > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch
