Re: [PATCH v3 11/12] drm/virtio: implement context init: add virtio_gpu_fence_event

[Daniel Vetter <daniel@ffwll.ch>]

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@chromium.org>
> > Acked-by: Nicholas Verne <nverne@chromium.org>
> > ---
> >  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