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

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