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From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Wed, 4 Apr 2018 14:26:13 +0200
Message-ID: <CAKMK7uEMsUOFDWishv6L0519Z7eiz+7LcHMpQAZu1bO7i2dVDA@mail.gmail.com>
Subject: Re: [RFC] drm/atomic+msm: add helper to implement legacy dirtyfb
To:     Rob Clark <robdclark@gmail.com>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        David Airlie <airlied@linux.ie>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Deepak Singh Rawat <drawat@vmware.com>,
        freedreno <freedreno@lists.freedesktop.org>,
        Lukasz Spintzyk <lukasz.spintzyk@displaylink.com>
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On Wed, Apr 4, 2018 at 2:05 PM, Rob Clark <robdclark@gmail.com> wrote:
> On Wed, Apr 4, 2018 at 7:49 AM, Maarten Lankhorst
> <maarten.lankhorst@linux.intel.com> wrote:
>> Op 04-04-18 om 13:37 schreef Rob Clark:
>>> On Wed, Apr 4, 2018 at 6:36 AM, Maarten Lankhorst
>>> <maarten.lankhorst@linux.intel.com> 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@gmail.com>
>>>>>>> ---
>>>>>>> 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 :-)
-Daniel

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