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

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