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From:   Rob Clark <robdclark@gmail.com>
Date:   Wed, 4 Apr 2018 07:37:33 -0400
Message-ID: <CAF6AEGvozzCDtkRjCjMsZ5HtdHXbFiiVM52jZaz=VfshONzqTA@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 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..

BR,
-R

>> - 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.
>>
>> 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
>
>