From: Gustavo Padovan <gustavo.pado...@collabora.com> Hi,
I renamed this back to RFC as many things are still under discussion/open but it integrates all comments received on the previous round[1]. My main goal now is to fit as many use cases as possible into this Explicit Synchronization implementation, but first I'd like to recap some detail of the implementation, as some pieces changed since the last patchset, that means the explanation on previous cover letters aren't entirely valid anymore. Explicit Synchronization allows us to control the synchronization of shared buffers from userspace by passing fences to the kernel and/or receiving them from it. Fences passed to the kernel are named in-fences and the kernel should wait them to signal before using the buffer, i.e., queueing it to the driver. On the other side, the kernel can create out-fences for the buffers it queues to the drivers, out-fences signal when the driver is finished with buffer, that is, the buffer is ready. Before we talk about more details, lets differentiate ordering concepts, there is two orthogonal places in the pipeline where buffers may or may not be ordered. Inside the drivers and inside vb2 core: * Ordering in the driver: In this RFC to use out-fences v4l2 drivers need to guarantee ordering of the buffers inside the driver, that is, buffers should become done (think calling vb2_buffer_done() here) in the same order they are queued to the driver. Drivers should set q->ordered_in_driver to 1 if they can keep ordering. (See patch 08/17) * Ordering in vb2: Some queues (OUTPUT queues and some m2m devices) requires that the order we queue buffers to the driver do not change in relation to the order they were queued from userspace. So that is marked in the code by q->is_output or q->ordered_in_vb2 and this implementation can work with both ordered and not-ordered queues at the vb2 level. (See patch 09/17) The in-fences are communicated at the VIDIOC_QBUF ioctl using the V4L2_BUF_FLAG_IN_FENCE buffer flag and the fence_fd field. If an in-fence needs to be passed to the kernel, fence_fd should be set to the fence file descriptor number and the V4L2_BUF_FLAG_IN_FENCE should be set as well. If ordered in vb2 needs to be kept we use fence arrays (see patch 12 and 13) Out-fence for a given buffer is enabled if the V4L2_BUF_FLAG_OUT_FENCE flag is passed in the QBUF() call and then communicated to userspace via the newly created V4L2_EVENT_OUT_FENCE event. The event is queued for userspace pick up when the buffer is queued to the driver, or if the queue is ordered both in the driver and vb2 we send the event right away. (see patch 14 to 16) Use cases --------- I believe use cases like camera app preview, photoshoot, video record, m2m color converters and scalers (with ordered queues) and output devices are covered by this RFC, but others like synchronized Audio/Video transmission doesn't seem to benefit too much from fences. Talking to Nicolas he expressed that fences are not really useful for such cases because we still need to sync with the Audio side, so may be we need wait at least for a start of streaming signal or something like that. For m2m encoders, we would be in a similar situation needing to know bytesused beforehand. I want to hear what others think here. WIP on V4L2 event ----------------- As the V4L2 event part is not the crucial part here, the current changes there to allow install the fence_fd at DQ_EVENT() are to be considered PoC. Suggestions are welcome. (See patch 4) Main Changes on v4 ------------------- * Keep ordering in vb2 of buffers queued from userspace with in-fence attached. This is necessary for OUTPUT and some m2m queues. * V4L2_EVENT_BUF_QUEUED event was renamed to V4L2_EVENT_OUT_FENCE and is only sent when an out-fence exists. * For queues that are both ordered in vb2 and in driver the OUT_FENCE event is sent out immediately without waiting for the buffer to be queued on the driver * The out-fence FD is only installed at DQ_EVENT(), but this implementation needs improvement. See 'Open Questions' * Refactor slightly event subscription for v4l2 driver, now there is a v4l2_event_subscribe_v4l2() that will subscribe for event that all devices need. * Protect dma_fence_remove_callback() with the fence lock. Only the most important changes are detailed here, for a full list of them, see each individual patch. Open Questions -------------- * synchronized Audio/Video transmission and m2m encoders use cases discussed above * V4L2 event: Improve solution to install the fd and figure how to clean up a event if userspace don't pick it up. Test tool --------- Test tool I've been using can be found at: https://git.collabora.com/cgit/user/padovan/v4l2-test.git/ Regards, Gustavo -- [1] https://lkml.org/lkml/2017/9/7/489 Gustavo Padovan (16): [media] v4l: create v4l2_event_subscribe_v4l2() [media] v4l: use v4l2_subscribe_event_v4l2() on vtables [media] v4l: use v4l2_subscribe_event_v4l2() on drivers WIP: [media] v4l2: add v4l2_event_queue_fh_with_cb() [media] v4l: add V4L2_EVENT_OUT_FENCE event [media] vb2: add .send_out_fence() to notify userspace of out_fence_fd [media] vivid: assign the specific device to the vb2_queue->dev [media] vb2: add 'ordered_in_driver' property to queues [media] vb2: add 'ordered_in_vb2' property to queues [media] vivid: mark vivid queues as ordered_in_driver [media] vb2: check earlier if stream can be started [media] vb2: add explicit fence user API [media] vb2: add in-fence support to QBUF [media] vb2: add infrastructure to support out-fences [media] vb2: add out-fence support to QBUF [media] v4l: Document explicit synchronization behaviour Javier Martinez Canillas (1): [media] vb2: add videobuf2 dma-buf fence helpers Documentation/media/uapi/v4l/buffer.rst | 15 ++ Documentation/media/uapi/v4l/vidioc-dqevent.rst | 23 ++ Documentation/media/uapi/v4l/vidioc-qbuf.rst | 31 +++ Documentation/media/videodev2.h.rst.exceptions | 1 + drivers/media/common/saa7146/saa7146_video.c | 4 +- drivers/media/dvb-frontends/rtl2832_sdr.c | 2 +- drivers/media/pci/bt8xx/bttv-driver.c | 4 +- drivers/media/pci/cobalt/cobalt-v4l2.c | 2 +- drivers/media/pci/cx18/cx18-ioctl.c | 2 +- drivers/media/pci/cx23885/cx23885-video.c | 2 +- drivers/media/pci/cx25821/cx25821-video.c | 2 +- drivers/media/pci/cx88/cx88-blackbird.c | 2 +- drivers/media/pci/cx88/cx88-video.c | 4 +- drivers/media/pci/ivtv/ivtv-ioctl.c | 2 +- drivers/media/pci/meye/meye.c | 2 +- drivers/media/pci/saa7134/saa7134-empress.c | 2 +- drivers/media/pci/saa7134/saa7134-video.c | 4 +- drivers/media/pci/saa7164/saa7164-encoder.c | 2 +- drivers/media/pci/solo6x10/solo6x10-v4l2.c | 2 +- drivers/media/pci/sta2x11/sta2x11_vip.c | 2 +- drivers/media/pci/tw5864/tw5864-video.c | 2 +- drivers/media/pci/tw68/tw68-video.c | 2 +- drivers/media/pci/tw686x/tw686x-video.c | 2 +- drivers/media/pci/zoran/zoran_driver.c | 2 +- drivers/media/platform/am437x/am437x-vpfe.c | 2 +- drivers/media/platform/atmel/atmel-isc.c | 2 +- drivers/media/platform/atmel/atmel-isi.c | 2 +- drivers/media/platform/coda/coda-common.c | 2 +- drivers/media/platform/fsl-viu.c | 2 +- drivers/media/platform/marvell-ccic/mcam-core.c | 2 +- drivers/media/platform/mtk-mdp/mtk_mdp_m2m.c | 2 +- drivers/media/platform/mtk-vcodec/mtk_vcodec_dec.c | 2 +- drivers/media/platform/mtk-vcodec/mtk_vcodec_enc.c | 2 +- drivers/media/platform/pxa_camera.c | 2 +- drivers/media/platform/qcom/venus/vdec.c | 4 +- drivers/media/platform/qcom/venus/venc.c | 2 +- drivers/media/platform/rcar-vin/rcar-v4l2.c | 2 +- drivers/media/platform/rcar_drif.c | 2 +- drivers/media/platform/rcar_fdp1.c | 2 +- drivers/media/platform/rcar_jpu.c | 2 +- drivers/media/platform/s3c-camif/camif-capture.c | 2 +- drivers/media/platform/sti/bdisp/bdisp-v4l2.c | 2 +- drivers/media/platform/sti/hva/hva-v4l2.c | 2 +- drivers/media/platform/stm32/stm32-dcmi.c | 2 +- drivers/media/platform/ti-vpe/cal.c | 2 +- drivers/media/platform/ti-vpe/vpe.c | 2 +- drivers/media/platform/vim2m.c | 2 +- drivers/media/platform/vivid/vivid-core.c | 15 +- drivers/media/platform/vivid/vivid-vid-out.c | 2 +- drivers/media/radio/dsbr100.c | 2 +- drivers/media/radio/radio-cadet.c | 2 +- drivers/media/radio/radio-isa.c | 2 +- drivers/media/radio/radio-keene.c | 2 +- drivers/media/radio/radio-ma901.c | 2 +- drivers/media/radio/radio-miropcm20.c | 2 +- drivers/media/radio/radio-mr800.c | 2 +- drivers/media/radio/radio-sf16fmi.c | 2 +- drivers/media/radio/radio-si476x.c | 2 +- drivers/media/radio/radio-tea5764.c | 2 +- drivers/media/radio/radio-tea5777.c | 2 +- drivers/media/radio/radio-timb.c | 2 +- drivers/media/radio/si470x/radio-si470x-common.c | 2 +- drivers/media/radio/si4713/radio-platform-si4713.c | 2 +- drivers/media/radio/si4713/radio-usb-si4713.c | 2 +- drivers/media/radio/tea575x.c | 2 +- drivers/media/usb/airspy/airspy.c | 2 +- drivers/media/usb/au0828/au0828-video.c | 2 +- drivers/media/usb/cpia2/cpia2_v4l.c | 4 +- drivers/media/usb/cx231xx/cx231xx-417.c | 2 +- drivers/media/usb/cx231xx/cx231xx-video.c | 4 +- drivers/media/usb/em28xx/em28xx-video.c | 4 +- drivers/media/usb/go7007/go7007-v4l2.c | 2 +- drivers/media/usb/gspca/gspca.c | 2 +- drivers/media/usb/hackrf/hackrf.c | 2 +- drivers/media/usb/hdpvr/hdpvr-video.c | 2 +- drivers/media/usb/msi2500/msi2500.c | 2 +- drivers/media/usb/pwc/pwc-v4l.c | 2 +- drivers/media/usb/s2255/s2255drv.c | 2 +- drivers/media/usb/stk1160/stk1160-v4l.c | 2 +- drivers/media/usb/stkwebcam/stk-webcam.c | 2 +- drivers/media/usb/tm6000/tm6000-video.c | 4 +- drivers/media/usb/usbvision/usbvision-video.c | 4 +- drivers/media/usb/uvc/uvc_v4l2.c | 2 +- drivers/media/usb/zr364xx/zr364xx.c | 2 +- drivers/media/v4l2-core/Kconfig | 1 + drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 4 +- drivers/media/v4l2-core/v4l2-event.c | 45 +++- drivers/media/v4l2-core/videobuf2-core.c | 239 +++++++++++++++++++-- drivers/media/v4l2-core/videobuf2-v4l2.c | 84 +++++++- .../vc04_services/bcm2835-camera/bcm2835-camera.c | 2 +- include/media/v4l2-event.h | 15 ++ include/media/videobuf2-core.h | 49 ++++- include/media/videobuf2-fence.h | 48 +++++ include/uapi/linux/videodev2.h | 16 +- samples/v4l/v4l2-pci-skeleton.c | 2 +- 95 files changed, 643 insertions(+), 125 deletions(-) create mode 100644 include/media/videobuf2-fence.h -- 2.13.6
