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From:   Rob Clark <robdclark@gmail.com>
Date:   Wed, 4 Apr 2018 08:05:16 -0400
Message-ID: <CAF6AEGtzFJwzgrH5TZn6QGLjkkOP7=XV4B1at6xxNvKrabNFww@mail.gmail.com>
Subject: Re: [RFC] drm/atomic+msm: add helper to implement legacy dirtyfb
To:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc:     dri-devel <dri-devel@lists.freedesktop.org>,
        freedreno <freedreno@lists.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>,
        Thomas Hellstrom <thomas@shipmail.org>,
        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        Lukasz Spintzyk <lukasz.spintzyk@displaylink.com>,
        Deepak Singh Rawat <drawat@vmware.com>,
        Gustavo Padovan <gustavo@padovan.org>,
        Sean Paul <seanpaul@chromium.org>,
        David Airlie <airlied@linux.ie>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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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

BR,
-R