Re: [RFC] drm/atomic+msm: add helper to implement legacy dirtyfb

From: Rob Clark
Date: Wed Apr 04 2018 - 07:36:08 EST

On Wed, Apr 4, 2018 at 6:21 AM, Daniel Vetter <daniel@xxxxxxxx> wrote:
> On Wed, Apr 04, 2018 at 12:03:00PM +0200, Daniel Vetter wrote:
>> On Tue, Apr 03, 2018 at 06:42:23PM -0400, Rob Clark wrote:
>> > Add an atomic helper to implement dirtyfb support. This is needed to
>> > support DSI command-mode panels with x11 userspace (ie. when we can't
>> > rely on pageflips to trigger a flush to the panel).
>> >
>> > To signal to the driver that the async atomic update needs to
>> > synchronize with fences, even though the fb didn't change, the
>> > drm_atomic_state::dirty flag is added.
>> >
>> > Signed-off-by: Rob Clark <robdclark@xxxxxxxxx>
>> > ---
>> > Background: there are a number of different folks working on getting
>> > upstream kernel working on various different phones/tablets with qcom
>> > SoC's.. many of them have command mode panels, so we kind of need a
>> > way to support the legacy dirtyfb ioctl for x11 support.
>> >
>> > I know there is work on a proprer non-legacy atomic property for
>> > userspace to communicate dirty-rect(s) to the kernel, so this can
>> > be improved from triggering a full-frame flush once that is in
>> > place. But we kinda needa a stop-gap solution.
>> >
>> > I had considered an in-driver solution for this, but things get a
>> > bit tricky if userspace ands up combining dirtyfb ioctls with page-
>> > flips, because we need to synchronize setting various CTL.FLUSH bits
>> > with setting the CTL.START bit. (ie. really all we need to do for
>> > cmd mode panels is bang CTL.START, but is this ends up racing with
>> > pageflips setting FLUSH bits, then bad things.) The easiest soln
>> > is to wrap this up as an atomic commit and rely on the worker to
>> > serialize things. Hence adding an atomic dirtyfb helper.
>> >
>> > I guess at least the helper, with some small addition to translate
>> > and pass-thru the dirty rect(s) is useful to the final atomic dirty-
>> > rect property solution. Depending on how far off that is, a stop-
>> > gap solution could be useful.
>> >
>> > drivers/gpu/drm/drm_atomic_helper.c | 66 +++++++++++++++++++++++++++++++++++++
>> > drivers/gpu/drm/msm/msm_atomic.c | 5 ++-
>> > drivers/gpu/drm/msm/msm_fb.c | 1 +
>> > include/drm/drm_atomic_helper.h | 4 +++
>> > include/drm/drm_plane.h | 9 +++++
>> > 5 files changed, 84 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
>> > index c35654591c12..a578dc681b27 100644
>> > --- a/drivers/gpu/drm/drm_atomic_helper.c
>> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
>> > @@ -3504,6 +3504,7 @@ void __drm_atomic_helper_plane_duplicate_state(struct drm_plane *plane,
>> > if (state->fb)
>> > drm_framebuffer_get(state->fb);
>> >
>> > + state->dirty = false;
>> > state->fence = NULL;
>> > state->commit = NULL;
>> > }
>> > @@ -3847,6 +3848,71 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
>> > }
>> > EXPORT_SYMBOL(drm_atomic_helper_legacy_gamma_set);
>> >
>> > +/**
>> > + * drm_atomic_helper_dirtyfb - helper for dirtyfb
>> > + *
>> > + * A helper to implement drm_framebuffer_funcs::dirty
>> > + */
>> > +int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
>> > + struct drm_file *file_priv, unsigned flags,
>> > + unsigned color, struct drm_clip_rect *clips,
>> > + unsigned num_clips)
>> > +{
>> > + struct drm_modeset_acquire_ctx ctx;
>> > + struct drm_atomic_state *state;
>> > + struct drm_plane *plane;
>> > + int ret = 0;
>> > +
>> > + /*
>> > + * When called from ioctl, we are interruptable, but not when
>> > + * called internally (ie. defio worker)
>> > + */
>> > + drm_modeset_acquire_init(&ctx,
>> > + file_priv ? DRM_MODESET_ACQUIRE_INTERRUPTIBLE : 0);
>> > +
>> > + state = drm_atomic_state_alloc(fb->dev);
>> > + if (!state) {
>> > + ret = -ENOMEM;
>> > + goto out;
>> > + }
>> > + state->acquire_ctx = &ctx;
>> > +
>> > +retry:
>> > + drm_for_each_plane(plane, fb->dev) {
>> > + struct drm_plane_state *plane_state;
>> > +
>> > + if (plane->state->fb != fb)
>> > + continue;
>> > +
>> > + plane_state = drm_atomic_get_plane_state(state, plane);
>> > + if (IS_ERR(plane_state)) {
>> > + ret = PTR_ERR(plane_state);
>> > + goto out;
>> > + }
>> > +
>> > + plane_state->dirty = true;
>> > + }
>> > +
>> > + ret = drm_atomic_nonblocking_commit(state);
>> > +
>> > +out:
>> > + if (ret == -EDEADLK) {
>> > + drm_atomic_state_clear(state);
>> > + ret = drm_modeset_backoff(&ctx);
>> > + if (!ret)
>> > + goto retry;
>> > + }
>> > +
>> > + drm_atomic_state_put(state);
>> > +
>> > + drm_modeset_drop_locks(&ctx);
>> > + drm_modeset_acquire_fini(&ctx);
>> > +
>> > + return ret;
>> > +
>> > +}
>> > +EXPORT_SYMBOL(drm_atomic_helper_dirtyfb);
>> > +
>> > /**
>> > * __drm_atomic_helper_private_duplicate_state - copy atomic private state
>> > * @obj: CRTC object
>> > diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
>> > index bf5f8c39f34d..bb55a048e98b 100644
>> > --- a/drivers/gpu/drm/msm/msm_atomic.c
>> > +++ b/drivers/gpu/drm/msm/msm_atomic.c
>> > @@ -201,7 +201,10 @@ int msm_atomic_commit(struct drm_device *dev,
>> > * Figure out what fence to wait for:
>> > */
>> > for_each_oldnew_plane_in_state(state, plane, old_plane_state, new_plane_state, i) {
>> > - if ((new_plane_state->fb != old_plane_state->fb) && new_plane_state->fb) {
>> > + bool sync_fb = new_plane_state->fb &&
>> > + ((new_plane_state->fb != old_plane_state->fb) ||
>> > + new_plane_state->dirty);
>>
>> Why do you have this optimization even here? Imo flipping to the same fb
>> should result in the fb getting fully uploaded, whether you're doing a
>> legacy page_flip, and atomic one or just a plane update.
>>
>> Iirc some userspace does use that as essentially a full-plane frontbuffer
>> rendering flush already. IOW I don't think we need your
>> plane_state->dirty, it's implied to always be true - why would userspace
>> do a flip otherwise?
>>
>> The helper itself to map dirtyfb to a nonblocking atomic commit looks
>> reasonable, but misses a bunch of the trickery discussed with Noralf and
>> others I think.
>
> Ok, I've done some history digging:
>
> - i915 and nouveau unconditionally wait for fences, even for same-fb
> flips.
> - no idea what amdgpu and vmwgfx are doing, they're not using
> plane_state->fence for implicit fences.
> - most arm-soc drivers do have this "optimization" in their code, and it
> even managed to get into the new drm_gem_fb_prepare_fb helper (which I
> reviewed, or well claimed to have ... oops). Afaict it goes back to the
> original msm atomic code, and was then dutifully copypasted all over the
> place.
>
> If folks are ok I'll do a patch series to align drivers with i915/nouveau.
> Well, any driver using reservation_object_get_excl_rcu +
> drm_atomic_set_fence_for_plane combo, since amdgpu and vmwgfx don't I have
> no idea what they're doing or whether they might have the same bug.

if you do a patch series, I think do it the other way around and align
to msm ;-)

I think otherwise we could end up stalling while x11 does front buffer
rendering for something unrelated (maybe I was hitting that with
cursor updates?)

BR,
-R

> From looking at at least the various prepare_fb callbacks I don't see any
> other drivers doing funny stuff around implicit fences.
> -Daniel
>
>> > + if (sync_fb) {
>> > struct drm_gem_object *obj = msm_framebuffer_bo(new_plane_state->fb, 0);
>> > struct msm_gem_object *msm_obj = to_msm_bo(obj);
>> > struct dma_fence *fence = reservation_object_get_excl_rcu(msm_obj->resv);
>> > diff --git a/drivers/gpu/drm/msm/msm_fb.c b/drivers/gpu/drm/msm/msm_fb.c
>> > index 0e0c87252ab0..a5d882a34a33 100644
>> > --- a/drivers/gpu/drm/msm/msm_fb.c
>> > +++ b/drivers/gpu/drm/msm/msm_fb.c
>> > @@ -62,6 +62,7 @@ static void msm_framebuffer_destroy(struct drm_framebuffer *fb)
>> > static const struct drm_framebuffer_funcs msm_framebuffer_funcs = {
>> > .create_handle = msm_framebuffer_create_handle,
>> > .destroy = msm_framebuffer_destroy,
>> > + .dirty = drm_atomic_helper_dirtyfb,
>> > };
>> >
>> > #ifdef CONFIG_DEBUG_FS
>> > diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h
>> > index 26aaba58d6ce..9b7a95c2643d 100644
>> > --- a/include/drm/drm_atomic_helper.h
>> > +++ b/include/drm/drm_atomic_helper.h
>> > @@ -183,6 +183,10 @@ int drm_atomic_helper_legacy_gamma_set(struct drm_crtc *crtc,
>> > u16 *red, u16 *green, u16 *blue,
>> > uint32_t size,
>> > struct drm_modeset_acquire_ctx *ctx);
>> > +int drm_atomic_helper_dirtyfb(struct drm_framebuffer *fb,
>> > + struct drm_file *file_priv, unsigned flags,
>> > + unsigned color, struct drm_clip_rect *clips,
>> > + unsigned num_clips);
>> > void __drm_atomic_helper_private_obj_duplicate_state(struct drm_private_obj *obj,
>> > struct drm_private_state *state);
>> >
>> > diff --git a/include/drm/drm_plane.h b/include/drm/drm_plane.h
>> > index f7bf4a48b1c3..296fa22bda7a 100644
>> > --- a/include/drm/drm_plane.h
>> > +++ b/include/drm/drm_plane.h
>> > @@ -76,6 +76,15 @@ struct drm_plane_state {
>> > */
>> > struct drm_framebuffer *fb;
>> >
>> > + /**
>> > + * @dirty:
>> > + *
>> > + * Flag that indicates the fb contents have changed even though the
>> > + * fb has not. This is mostly a stop-gap solution until we have
>> > + * atomic dirty-rect(s) property.
>> > + */
>> > + bool dirty;
>> > +
>> > /**
>> > * @fence:
>> > *
>> > --
>> > 2.14.3
>> >
>>
>> --
>> Daniel Vetter
>> Software Engineer, Intel Corporation
>> http://blog.ffwll.ch
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch