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Subject: Re: [RFC] drm/atomic+msm: add helper to implement legacy dirtyfb
To:     Rob Clark <robdclark@gmail.com>, dri-devel@lists.freedesktop.org,
        freedreno@lists.freedesktop.org, 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@vger.kernel.org
References: <20180403224225.26776-1-robdclark@gmail.com>
 <20180404100300.GE3881@phenom.ffwll.local>
 <20180404102108.GF3881@phenom.ffwll.local>
From:   Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Message-ID: <4976c166-32b2-75ef-ee78-7e7893dd4121@linux.intel.com>
Date:   Wed, 4 Apr 2018 12:36:12 +0200
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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..
> - 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