Hi Ville,
2017-04-27 Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>:
> On Thu, Apr 27, 2017 at 12:15:13PM -0300, Gustavo Padovan wrote:
> > From: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>
> >
> > In some cases, like cursor updates, it is interesting to update the
> > plane in an asynchronous fashion to avoid big delays. The current queued
> > update could be still waiting for a fence to signal and thus block any
> > subsequent update until its scan out. In cases like this if we update the
> > cursor synchronously through the atomic API it will cause significant
> > delays that would even be noticed by the final user.
> >
> > This patch creates a fast path to jump ahead the current queued state and
> > do single planes updates without going through all atomic step in
> > drm_atomic_helper_commit().
> >
> > We take this path for legacy cursor updates. Users can also set the
> > DRM_MODE_ATOMIC_ASYNC_UPDATE flag on atomic updates.
> >
> > For now only single plane updates are supported, but we plan to support
> > multiple planes updates and async PageFlips through this interface as well
> > in the near future.
> >
> > v2:
> > - allow updates even if there is a queued update for the same
> > plane.
> > - fixes on the documentation (Emil Velikov)
> > - unconditionally call ->atomic_async_update (Emil Velikov)
> > - check for ->atomic_async_update earlier (Daniel Vetter)
> > - make ->atomic_async_check() the last step (Daniel Vetter)
> > - add ASYNC_UPDATE flag (Eric Anholt)
> > - update state in core after ->atomic_async_update (Eric Anholt)
> > - update docs (Eric Anholt)
> >
> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
> > Cc: Rob Clark <robdclark@xxxxxxxxx>
> > Cc: Eric Anholt <eric@xxxxxxxxxx>
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/drm_atomic.c | 50 ++++++++++++++++++++++++++++++++
> > drivers/gpu/drm/drm_atomic_helper.c | 48 ++++++++++++++++++++++++++++++
> > include/drm/drm_atomic.h | 2 ++
> > include/drm/drm_atomic_helper.h | 2 ++
> > include/drm/drm_modeset_helper_vtables.h | 45 ++++++++++++++++++++++++++++
> > include/uapi/drm/drm_mode.h | 4 ++-
> > 6 files changed, 150 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
> > index 30229ab..7b60cf8 100644
> > --- a/drivers/gpu/drm/drm_atomic.c
> > +++ b/drivers/gpu/drm/drm_atomic.c
> > @@ -77,6 +77,7 @@ drm_atomic_state_init(struct drm_device *dev, struct drm_atomic_state *state)
> > * setting this appropriately?
> > */
> > state->allow_modeset = true;
> > + state->async_update = true;
> >
> > state->crtcs = kcalloc(dev->mode_config.num_crtc,
> > sizeof(*state->crtcs), GFP_KERNEL);
> > @@ -631,6 +632,51 @@ static int drm_atomic_crtc_check(struct drm_crtc *crtc,
> > return 0;
> > }
> >
> > +static bool drm_atomic_async_check(struct drm_atomic_state *state)
> > +{
> > + struct drm_crtc *crtc;
> > + struct drm_crtc_state *crtc_state;
> > + struct drm_plane *__plane, *plane = NULL;
> > + struct drm_plane_state *__plane_state, *plane_state = NULL;
> > + const struct drm_plane_helper_funcs *funcs;
> > + int i, n_planes = 0;
> > +
> > + for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
> > + if (drm_atomic_crtc_needs_modeset(crtc_state))
> > + return false;
> > + }
> > +
> > + for_each_new_plane_in_state(state, __plane, __plane_state, i) {
> > + n_planes++;
> > + plane = __plane;
> > + plane_state = __plane_state;
> > + }
> > +
> > + /* FIXME: we support single plane updates for now */
> > + if (!plane || n_planes != 1)
> > + return false;
> > +
> > + funcs = plane->helper_private;
> > + if (!funcs->atomic_async_update)
> > + return false;
> > +
> > + if (plane_state->fence)
> > + return false;
> > +
> > + if (!plane->state->crtc || (plane->state->crtc != plane_state->crtc))
> > + return false;
> > +
> > + /* No configuring new scaling in the async path. */
>
> Those checks aren't really about scaling. Well, they are also about
> scaling, but they're mainly about changing size.
I just copied the comment from the previous code in the drivers...
I can fix it.
>
> What I don't really understand is why we're enforcing these restrictions
> in the core but leaving other restrictions up to the driver. I don't see
> size changes as anything really special compared to many of the other
> restrictions that would now be up to each driver.
Because I extracted what was common between msm, vc4 and i915 on their
legacy cursor update calls. I didn't want to enforce anything else in
core for now.
>
> If you're really after some lowest common denominator as far as
> exposed capabilities are concerned then I think the core should do
> more checking. OTOH if you're not interested limiting what each
> driver exposes then I don't see why the core checks anything at all.
I think a common denominator is what we want but we only have 3 drivers
using it at the moment. We can look for more checks that shoud be done
is core. Any suggestions?
>
> > + if (plane->state->crtc_w != plane_state->crtc_w ||
> > + plane->state->crtc_h != plane_state->crtc_h ||
> > + plane->state->src_w != plane_state->src_w ||
> > + plane->state->src_h != plane_state->src_h) {
> > + return false;
> > + }
> > +
> > + return !funcs->atomic_async_check(plane, plane_state);
> > +}
> > +
> > static void drm_atomic_crtc_print_state(struct drm_printer *p,
> > const struct drm_crtc_state *state)
> > {
> <snip>
> > /**
> > diff --git a/include/uapi/drm/drm_mode.h b/include/uapi/drm/drm_mode.h
> > index 8c67fc0..7c067ca 100644
> > --- a/include/uapi/drm/drm_mode.h
> > +++ b/include/uapi/drm/drm_mode.h
> > @@ -646,13 +646,15 @@ struct drm_mode_destroy_dumb {
> > #define DRM_MODE_ATOMIC_TEST_ONLY 0x0100
> > #define DRM_MODE_ATOMIC_NONBLOCK 0x0200
> > #define DRM_MODE_ATOMIC_ALLOW_MODESET 0x0400
> > +#define DRM_MODE_ATOMIC_ASYNC_UPDATE 0x0800
>
> What exactly is that flag supposed to mean?
I don't think I provided a good explanation for it, sorry. This flag
tells core to jump ahead the queued update if the conditions in
drm_atomic_async_check() are met. Useful for cursors and async PageFlips
over the atomic ioctl.
Gustavo
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