Messages in this thread | | | From | "Kazlauskas, Nicholas" <> | Subject | Re: [PATCH 1/5] drm: don't block fb changes for async plane updates | Date | Mon, 4 Mar 2019 15:46:49 +0000 |
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On 3/4/19 9:49 AM, Helen Koike wrote: > In the case of a normal sync update, the preparation of framebuffers (be > it calling drm_atomic_helper_prepare_planes() or doing setups with > drm_framebuffer_get()) are performed in the new_state and the respective > cleanups are performed in the old_state. > > In the case of async updates, the preparation is also done in the > new_state but the cleanups are done in the new_state (because updates > are performed in place, i.e. in the current state). > > The current code blocks async udpates when the fb is changed, turning > async updates into sync updates, slowing down cursor updates and > introducing regressions in igt tests with errors of type: > > "CRITICAL: completed 97 cursor updated in a period of 30 flips, we > expect to complete approximately 15360 updates, with the threshold set > at 7680" > > Fb changes in async updates were prevented to avoid the following scenario: > > - Async update, oldfb = NULL, newfb = fb1, prepare fb1, cleanup fb1 > - Async update, oldfb = fb1, newfb = fb2, prepare fb2, cleanup fb2 > - Non-async commit, oldfb = fb2, newfb = fb1, prepare fb1, cleanup fb2 (wrong) > Where we have a single call to prepare fb2 but double cleanup call to fb2. > > To solve the above problems, instead of blocking async fb changes, we > place the old framebuffer in the new_state object, so when the code > performs cleanups in the new_state it will cleanup the old_fb and we > will have the following scenario instead: > > - Async update, oldfb = NULL, newfb = fb1, prepare fb1, no cleanup > - Async update, oldfb = fb1, newfb = fb2, prepare fb2, cleanup fb1 > - Non-async commit, oldfb = fb2, newfb = fb1, prepare fb1, cleanup fb2 > > Where calls to prepare/cleanup are ballanced. > > Cc: <stable@vger.kernel.org> # v4.14+: 25dc194b34dd: drm: Block fb changes for async plane updates > Fixes: 25dc194b34dd ("drm: Block fb changes for async plane updates") > Suggested-by: Boris Brezillon <boris.brezillon@collabora.com> > Signed-off-by: Helen Koike <helen.koike@collabora.com> > > --- > Hello, > > As mentioned in the cover letter, > I tested on the rockchip and on i915 (with a patch I am still working on for > replacing cursors by async update), with igt plane_cursor_legacy and > kms_cursor_legacy and I didn't see any regressions. > I couldn't test on MSM and AMD because I don't have the hardware (and I am > having some issues testing on vc4) and I would appreciate if anyone could help > me testing those. > > I also think it would be a better solution if, instead of having async > to do in-place updates in the current state, the async path should be > equivalent to a syncronous update, i.e., modifying new_state and > performing a flip > IMHO, the only difference between sync and async should be that async update > doesn't wait for vblank and applies the changes immeditally to the hw, > but the code path could be almost the same. > But for now I think this solution is ok (swaping new_fb/old_fb), and > then we can adjust things little by little, what do you think? > > Thanks! > Helen > > drivers/gpu/drm/drm_atomic_helper.c | 20 ++++++++++---------- > 1 file changed, 10 insertions(+), 10 deletions(-) > > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c > index 540a77a2ade9..e7eb96f1efc2 100644 > --- a/drivers/gpu/drm/drm_atomic_helper.c > +++ b/drivers/gpu/drm/drm_atomic_helper.c > @@ -1608,15 +1608,6 @@ int drm_atomic_helper_async_check(struct drm_device *dev, > old_plane_state->crtc != new_plane_state->crtc) > return -EINVAL; > > - /* > - * FIXME: Since prepare_fb and cleanup_fb are always called on > - * the new_plane_state for async updates we need to block framebuffer > - * changes. This prevents use of a fb that's been cleaned up and > - * double cleanups from occuring. > - */ > - if (old_plane_state->fb != new_plane_state->fb) > - return -EINVAL; > - > funcs = plane->helper_private; > if (!funcs->atomic_async_update) > return -EINVAL; > @@ -1657,6 +1648,9 @@ void drm_atomic_helper_async_commit(struct drm_device *dev, > int i; > > for_each_new_plane_in_state(state, plane, plane_state, i) { > + struct drm_framebuffer *new_fb = plane_state->fb; > + struct drm_framebuffer *old_fb = plane->state->fb; > + > funcs = plane->helper_private; > funcs->atomic_async_update(plane, plane_state); > > @@ -1665,11 +1659,17 @@ void drm_atomic_helper_async_commit(struct drm_device *dev, > * plane->state in-place, make sure at least common > * properties have been properly updated. > */ > - WARN_ON_ONCE(plane->state->fb != plane_state->fb); > + WARN_ON_ONCE(plane->state->fb != new_fb); > WARN_ON_ONCE(plane->state->crtc_x != plane_state->crtc_x); > WARN_ON_ONCE(plane->state->crtc_y != plane_state->crtc_y); > WARN_ON_ONCE(plane->state->src_x != plane_state->src_x); > WARN_ON_ONCE(plane->state->src_y != plane_state->src_y); > + > + /* > + * Make sure the FBs have been swapped so that cleanups in the > + * new_state performs a cleanup in the old FB. > + */ > + WARN_ON_ONCE(plane_state->fb != old_fb);
I personally think this approach is fine and the WARN_ON s are good for catching drivers that want to use these in the future.
I do think it would be good to add something to the function docs that explains this requirement and the issue that it addresses. It's a little unintuitive to require that the old fb is placed into the new state, but it makes sense as a workaround to this problem.
Nicholas Kazlauskas
> } > } > EXPORT_SYMBOL(drm_atomic_helper_async_commit); >
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