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

From: Rob Clark
Date: Wed Apr 04 2018 - 09:26:20 EST

On Wed, Apr 4, 2018 at 8:26 AM, Daniel Vetter <daniel@xxxxxxxx> wrote:
> On Wed, Apr 4, 2018 at 2:05 PM, Rob Clark <robdclark@xxxxxxxxx> wrote:
>> On Wed, Apr 4, 2018 at 7:49 AM, Maarten Lankhorst
>> <maarten.lankhorst@xxxxxxxxxxxxxxx> wrote:
>>> Op 04-04-18 om 13:37 schreef Rob Clark:
>>>> On Wed, Apr 4, 2018 at 6:36 AM, Maarten Lankhorst
>>>> <maarten.lankhorst@xxxxxxxxxxxxxxx> wrote:
>>>>> Op 04-04-18 om 12:21 schreef Daniel Vetter:
>>>>>> 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.
>>>>> I thought plane_state->fence was used for explicit fences, so its use by drivers
>>>>> would interfere with it? I don't think fencing would work on msm or vc4..
>>>> for implicit fencing we fish out the implicit fence and stuff it in
>>>> plane_state->fence..
>>> What happens when userspace passes a fence fd to in_fence_fd?
>>
>> mixing implicit sync and explicit sync is undefined
>
> It's very well-defined, explicit sync wins. See the kerneldoc for
> drm_atomic_set_fence_for_plane. Since a pile of drivers don't use that
> the reality might be undefined though :-)

ahh, msm_atomic does do drm_atomic_set_fence_for_plane() for
fished-out-fences so if that dtrt, it should be good..

BR,
-R

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