[PATCH] drm/cirrus: Let DRM core send VBLANK events

[Daniel Vetter]

On Mon, Jan 13, 2020 at 10:01 AM Thomas Zimmermann <tzimmermann at suse.de> wrote:
>
> Hi
>
> Am 13.01.20 um 00:00 schrieb Daniel Vetter:
> > On Fri, Jan 10, 2020 at 12:57:07PM +0100, Thomas Zimmermann wrote:
> >> In drm_atomic_helper_fake_vblank() the DRM core sends out VBLANK
> >> events if struct drm_crtc_state.no_vblank is enabled. Replace cirrus'
> >> VBLANK events with the DRM core's functionality.
> >>
> >> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> >> ---
> >>  drivers/gpu/drm/cirrus/cirrus.c | 10 ++--------
> >>  1 file changed, 2 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/cirrus/cirrus.c b/drivers/gpu/drm/cirrus/cirrus.c
> >> index 248c9f765c45..4a1729aa7e53 100644
> >> --- a/drivers/gpu/drm/cirrus/cirrus.c
> >> +++ b/drivers/gpu/drm/cirrus/cirrus.c
> >> @@ -38,7 +38,6 @@
> >>  #include <drm/drm_modeset_helper_vtables.h>
> >>  #include <drm/drm_probe_helper.h>
> >>  #include <drm/drm_simple_kms_helper.h>
> >> -#include <drm/drm_vblank.h>
> >>
> >>  #define DRIVER_NAME "cirrus"
> >>  #define DRIVER_DESC "qemu cirrus vga"
> >> @@ -415,6 +414,8 @@ static void cirrus_pipe_enable(struct drm_simple_display_pipe *pipe,
> >>  {
> >>      struct cirrus_device *cirrus = pipe->crtc.dev->dev_private;
> >>
> >> +    crtc_state->no_vblank = true;
> >
> > Huh, nice untended use of this stuff ... We've added this for writeback,
> > but I guess it can be used for anything that's a virtual connector ...
>
> Oh, 'improved by accident'.
>
> I'm not quite sure what you mean by virtual connector, but it should
> work with any CRTC without VBLANK support. At least I've never seen any
> problem with ast and udl. I'll update the docs accordingly.

There's a pretty huge difference between "real vblank support", which
means the various vblank/crtc_sequence ioctls work, and the fake
vblank even stuff we send out for all drivers right away to fulfill
the atomic uapi event requirements. We'll need to highlight that stuff
in the documentation I think ... On second thought, maybe we could
change the atomic helpers to automatically set no_vblank when the
driver/crtc doesn't support real vblanks. But is even more involved
(but I think might also be the even neater soluation, but hard to be
sure without typing it all up). Oh and because hilarious historical
accents "no real vblank" = drm_dev->num_crtcs == 0, which we might
want to put into a helper if we leak this out of the drm_vblank.c
source files.

Cheers, Daniel

>
> Best regards
> Thomas
>
> >
> > I've also spotted that you've done this same trick for ast & udl already.
> > But I think before we roll this out massively we should make this
> > official. Can you pls do a patch to update the kerneldoc for @no_vblank
> > that virtual hw can also use this stuff?
> >
> > Also, computing state values in atomic_commit code is kinda uncool and
> > fraught with peril - design assumption is that with some very few
> > exceptions (which are kinda awkward, would be nice to make state pointers
> > const) all the core and helper codes that state structures stay unchanged
> > after atomic_check completed. This should be computed in atomic_check (like vc4
> > does). Can you pls also include patches to update ast and udl in this
> > series?
> >
> > Thanks, Daniel
> >
> >
> >> +
> >>      cirrus_mode_set(cirrus, &crtc_state->mode, plane_state->fb);
> >>      cirrus_fb_blit_fullscreen(plane_state->fb);
> >>  }
> >> @@ -434,13 +435,6 @@ static void cirrus_pipe_update(struct drm_simple_display_pipe *pipe,
> >>
> >>      if (drm_atomic_helper_damage_merged(old_state, state, &rect))
> >>              cirrus_fb_blit_rect(pipe->plane.state->fb, &rect);
> >> -
> >> -    if (crtc->state->event) {
> >> -            spin_lock_irq(&crtc->dev->event_lock);
> >> -            drm_crtc_send_vblank_event(crtc, crtc->state->event);
> >> -            crtc->state->event = NULL;
> >> -            spin_unlock_irq(&crtc->dev->event_lock);
> >> -    }
> >>  }
> >>
> >>  static const struct drm_simple_display_pipe_funcs cirrus_pipe_funcs = {
> >> --
> >> 2.24.1
> >>
> >
>
> --
> Thomas Zimmermann
> Graphics Driver Developer
> SUSE Software Solutions Germany GmbH
> Maxfeldstr. 5, 90409 Nürnberg, Germany
> (HRB 36809, AG Nürnberg)
> Geschäftsführer: Felix Imendörffer
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch