On Thu, Nov 18, 2021 at 12:53 AM Daniel Vetter <daniel@xxxxxxxx> wrote: > > On Tue, Nov 16, 2021 at 06:31:10PM -0800, Gurchetan Singh wrote: > > On Tue, Nov 16, 2021 at 7:43 AM Daniel Vetter <daniel@xxxxxxxx> wrote: > > > > > On Mon, Nov 15, 2021 at 07:26:14PM +0000, Kasireddy, Vivek wrote: > > > > Hi Daniel, Greg, > > > > > > > > If it is the same or a similar crash reported here: > > > > > > > https://lists.freedesktop.org/archives/dri-devel/2021-November/330018.html > > > > and here: > > > https://lists.freedesktop.org/archives/dri-devel/2021-November/330212.html > > > > then the fix is already merged: > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d89c0c8322ecdc9a2ec84b959b6f766be082da76 > > > > Yeah but that still leaves the problem of why exaxtly virtgpu is > > > reinventing drm_poll here? > > > > > > > Can you please replace it with drm_poll like all other drivers, including > > > the ones that have private events? > > > > > > > Hi Daniel, > > > > Allow me to explain the use case a bit. It's for when virtgpu KMS is not > > used, but a special Wayland compositor does wayland passthrough instead: > > > > https://www.youtube.com/watch?v=WwrXqDERFm8https://www.youtube.com/watch?v=EkNBsBx501Q > > > > This technique has gained much popularity in the virtualized laptop > > space, where it offers better performance/user experience than virtgpu > > KMS. The relevant paravirtualized userspace is "Sommelier": > > > > https://chromium.googlesource.com/chromiumos/platform2/+/main/vm_tools/sommelier/ > > https://chromium.googlesource.com/chromiumos/platform2/+/main/vm_tools/sommelier/virtualization/virtgpu_channel.cc > > > > Previously, we were using the out-of-tree virtio-wl device and there > > were many discussions on how we could get this upstream: > > > > https://lists.freedesktop.org/archives/dri-devel/2017-December/160309.html > > https://lists.oasis-open.org/archives/virtio-dev/202002/msg00005.html > > > > Extending virtgpu was deemed the least intrusive option: > > > > https://www.spinics.net/lists/kvm/msg159206.html > > > > We ultimately settled on the context type abstraction and used > > virtio_gpu_poll to tell the guest "hey, we have a Wayland event". The > > host response is actually in a buffer of type BLOB_MEM_GUEST. > > > > It is possible to use drm_poll(..), but that would have to be > > accompanied by a drm_read(..). You'll need to define a dummy > > VIRTGPU_EVENT_FENCE_SIGNALED in the uapi too. > > > > That's originally how I did it, but some pointed out that's > > unnecessary since the host response is in the BLOB_MEM_GUEST buffer > > and virtgpu event is a dummy event. So we decided just to modify > > virtio_gpu_poll(..) to have the desired semantics in that case. > > > > For the regular virtio-gpu KMS path, things remain unchanged. > > > > There are of course other ways to do it (perhaps polling a dma_fence), > > but that was the cleanest way we could find. > > > > It's not rare for virtio to "special things" (see virtio_dma_buf_ops, > > virtio_dma_ops), since they are in fake devices. > > These are all internal interfaces, not uapi. > > > We're open to other ideas, but hopefully that answers some of your > > questions. > > Well for one, why does the commit message not explain any of this. You're > building uapi, which is forever, it's paramount all considerations are > properly explained. > > Second, I really don't like that youre redefining poll semantics in > incompatible ways from all other drm drivers. If you want special poll > semantics then just create a sperate fd for that (or a dma_fence or > whatever, maybe that saves some typing), but bending the drm fd semantics > is no good at all. We have tons of different fd with their dedicated > semantics in drm, trying to shoehorn it all into one just isn't very good > design. > > Or do the dummy event which is just the event code, but does not contain > any data. Either is fine with me. > > Can you pls do this asap? I really don't want to bake this in as uapi > which we then have to quirk and support forever. I'd say revert for -rc2 > of these two and then maybe sort it out properly in -next. I think as a general rule, if there is not consensus about uabi change, even if it is just a semantic change, then revert and reland later is ok.. As far as dummy VIRTGPU_EVENT_FENCE_SIGNALED.. that doesn't entirely sound like a bad thing to me. Actually, it sounds like a good thing.. it makes it more explicit what is going on. And would avoid confusing a different userspace polling for kms related events expecting to be able to do a read. BR, -R > Cheers, Daniel > > > > > > > Thanks, Daniel > > > > > > > > > > > Thanks, > > > > Vivek > > > > > > > > > On Sat, Nov 13, 2021 at 03:51:48PM +0100, Greg KH wrote: > > > > > > On Tue, Sep 21, 2021 at 04:20:23PM -0700, Gurchetan Singh wrote: > > > > > > > Similar to DRM_VMW_EVENT_FENCE_SIGNALED. Sends a pollable event > > > > > > > to the DRM file descriptor when a fence on a specific ring is > > > > > > > signaled. > > > > > > > > > > > > > > One difference is the event is not exposed via the UAPI -- this is > > > > > > > because host responses are on a shared memory buffer of type > > > > > > > BLOB_MEM_GUEST [this is the common way to receive responses with > > > > > > > virtgpu]. As such, there is no context specific read(..) > > > > > > > implementation either -- just a poll(..) implementation. > > > > > > > > > > > > > > Signed-off-by: Gurchetan Singh <gurchetansingh@xxxxxxxxxxxx> > > > > > > > Acked-by: Nicholas Verne <nverne@xxxxxxxxxxxx> > > > > > > > --- > > > > > > > drivers/gpu/drm/virtio/virtgpu_drv.c | 43 > > > +++++++++++++++++++++++++- > > > > > > > drivers/gpu/drm/virtio/virtgpu_drv.h | 7 +++++ > > > > > > > drivers/gpu/drm/virtio/virtgpu_fence.c | 10 ++++++ > > > > > > > drivers/gpu/drm/virtio/virtgpu_ioctl.c | 34 ++++++++++++++++++++ > > > > > > > 4 files changed, 93 insertions(+), 1 deletion(-) > > > > > > > > > > > > This commit seems to cause a crash in a virtual drm gpu driver for > > > > > > Android. I have reverted this, and the next commit in the series > > > from > > > > > > Linus's tree and all is good again. > > > > > > > > > > > > Any ideas? > > > > > > > > > > Well no, but also this patch looks very questionable of hand-rolling > > > > > drm_poll. Yes you can do driver private events like > > > > > DRM_VMW_EVENT_FENCE_SIGNALED, that's fine. But you really should not > > > need > > > > > to hand-roll the poll callback. vmwgfx (which generally is a very old > > > > > driver which has lots of custom stuff, so not a great example) doesn't > > > do > > > > > that either. > > > > > > > > > > So that part should go no matter what I think. > > > > > -Daniel > > > > > -- > > > > > Daniel Vetter > > > > > Software Engineer, Intel Corporation > > > > > http://blog.ffwll.ch > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > http://blog.ffwll.ch > > > > > -- > Daniel Vetter > Software Engineer, Intel Corporation > http://blog.ffwll.ch
