Hey Shengjiu,
first of all thanks for all of this work and I am very sorry for only emerging this late into the series, I sadly didn't notice it earlier.
I would like to voice a few concerns about the general idea of adding Audio support to the Media subsystem.
1. The biggest objection is, that the Linux Kernel has a subsystem specifically targeted for audio devices, adding support for these devices in another subsystem are counterproductive as they work around the shortcomings of the audio subsystem while forcing support for a device into a subsystem that was never designed for such devices. Instead, the audio subsystem has to be adjusted to be able to support all of the required workflows, otherwise, the next audio driver with similar requirements will have to move to the media subsystem as well, the audio subsystem would then never experience the required change and soon we would have two audio subsystems.
2. Closely connected to the previous objection, the media subsystem with its current staff of maintainers is overworked and barely capable of handling the workload, which includes an abundance of different devices from DVB, codecs, cameras, PCI devices, radio tuners, HDMI CEC, IR receivers, etc. Adding more device types to this matrix will make the situation worse and should only be done with a plan for how first to improve the current maintainer situation.
3. By using the same framework and APIs as the video codecs, the audio codecs are going to cause extra work for the video codec developers and maintainers simply by occupying the same space that was orginally designed for the purpose of video only. Even if you try to not cause any extra stress the simple presence of the audio code in the codebase is going to cause restrictions.
The main issue here is that the audio subsystem doesn't provide a mem2mem framework and I would say you are in luck because the media subsystem has gathered a lot of shortcomings with its current implementation of the mem2mem framework over time, which is why a new implementation will be necessary anyway.
So instead of hammering a driver into the wrong destination, I would suggest bundling our forces and implementing a general memory-to-memory framework that both the media and the audio subsystem can use, that addresses the current shortcomings of the implementation and allows you to upload the driver where it is supposed to be. This is going to cause restrictions as well, like mentioned in the concern number 3, but with the difference that we can make a general plan for such a framework that accomodates lots of use cases and each subsystem can add their routines on top of the general framework.
Another possible alternative is to try and make the DRM scheduler more generally available, this scheduler is the most mature and in fact is very similar to what you and what the media devices need. Which again just shows how common your usecase actually is and how a general solution is the best long term solution.
Please notice that Daniel Almeida is currently working on something related to this: https://lore.kernel.org/linux-media/3F80AC0D-DCAA-4EDE-BF58-BB1369C7EDCA@col...
If the toplevel maintainers decide to add the patchset so be it, but I wanted to voice my concerns and also highlight that this is likely going to cause extra stress for the video codecs maintainers and the maintainers in general. We cannot spend a lot of time on audio codecs, as video codecs already fill up our available time sufficiently, so the use of the framework needs to be conservative and cause as little extra work as possible for the original use case of the framework.
Regards, Sebastian
On 19.03.2024 15:50, Shengjiu Wang wrote:
Audio signal processing also has the requirement for memory to memory similar as Video.
This asrc memory to memory (memory ->asrc->memory) case is a non real time use case.
User fills the input buffer to the asrc module, after conversion, then asrc sends back the output buffer to user. So it is not a traditional ALSA playback and capture case.
It is a specific use case, there is no reference in current kernel. v4l2 memory to memory is the closed implementation, v4l2 current support video, image, radio, tuner, touch devices, so it is not complicated to add support for this specific audio case.
Because we had implemented the "memory -> asrc ->i2s device-> codec" use case in ALSA. Now the "memory->asrc->memory" needs to reuse the code in asrc driver, so the first 3 patches is for refining the code to make it can be shared by the "memory->asrc->memory" driver.
The main change is in the v4l2 side, A /dev/vl4-audioX will be created, user applications only use the ioctl of v4l2 framework.
Other change is to add memory to memory support for two kinds of i.MX ASRC module.
changes in v15:
- update MAINTAINERS for imx-asrc.c and vim2m-audio.c
changes in v14:
- document the reservation of 'AUXX' fourcc format.
- add v4l2_audfmt_to_fourcc() definition.
changes in v13
- change 'pixelformat' to 'audioformat' in dev-audio-mem2mem.rst
- add more description for clock drift in ext-ctrls-audio-m2m.rst
- Add "media: v4l2-ctrls: add support for fraction_bits" from Hans
to avoid build issue for kernel test robot
changes in v12
- minor changes according to comments
- drop min_buffers_needed = 1 and V4L2_CTRL_FLAG_UPDATE flag
- drop bus_info
changes in v11
- add add-fixed-point-test-controls in vivid.
- add v4l2_ctrl_fp_compose() helper function for min and max
changes in v10
- remove FIXED_POINT type
- change code base on media: v4l2-ctrls: add support for fraction_bits
- fix issue reported by kernel test robot
- remove module_alias
changes in v9:
- add MEDIA_ENT_F_PROC_AUDIO_RESAMPLER.
- add MEDIA_INTF_T_V4L_AUDIO
- add media controller support
- refine the vim2m-audio to support 8k<->16k conversion.
changes in v8:
- refine V4L2_CAP_AUDIO_M2M to be 0x00000008
- update doc for FIXED_POINT
- address comments for imx-asrc
changes in v7:
- add acked-by from Mark
- separate commit for fixed point, m2m audio class, audio rate controls
- use INTEGER_MENU for rate, FIXED_POINT for rate offset
- remove used fmts
- address other comments for Hans
changes in v6:
- use m2m_prepare/m2m_unprepare/m2m_start/m2m_stop to replace
m2m_start_part_one/m2m_stop_part_one, m2m_start_part_two/m2m_stop_part_two.
- change V4L2_CTRL_TYPE_ASRC_RATE to V4L2_CTRL_TYPE_FIXED_POINT
- fix warning by kernel test rebot
- remove some unused format V4L2_AUDIO_FMT_XX
- Get SNDRV_PCM_FORMAT from V4L2_AUDIO_FMT in driver.
- rename audm2m to viaudm2m.
changes in v5:
- remove V4L2_AUDIO_FMT_LPCM
- define audio pixel format like V4L2_AUDIO_FMT_S8...
- remove rate and format in struct v4l2_audio_format.
- Add V4L2_CID_ASRC_SOURCE_RATE and V4L2_CID_ASRC_DEST_RATE controls
- updata document accordingly.
changes in v4:
- update document style
- separate V4L2_AUDIO_FMT_LPCM and V4L2_CAP_AUDIO_M2M in separate commit
changes in v3:
- Modify documents for adding audio m2m support
- Add audio virtual m2m driver
- Defined V4L2_AUDIO_FMT_LPCM format type for audio.
- Defined V4L2_CAP_AUDIO_M2M capability type for audio m2m case.
- with modification in v4l-utils, pass v4l2-compliance test.
changes in v2:
- decouple the implementation in v4l2 and ALSA
- implement the memory to memory driver as a platfrom driver
and move it to driver/media
- move fsl_asrc_common.h to include/sound folder
Hans Verkuil (1): media: v4l2-ctrls: add support for fraction_bits
Shengjiu Wang (15): ASoC: fsl_asrc: define functions for memory to memory usage ASoC: fsl_easrc: define functions for memory to memory usage ASoC: fsl_asrc: move fsl_asrc_common.h to include/sound ASoC: fsl_asrc: register m2m platform device ASoC: fsl_easrc: register m2m platform device media: uapi: Add V4L2_CAP_AUDIO_M2M capability flag media: v4l2: Add audio capture and output support media: uapi: Define audio sample format fourcc type media: uapi: Add V4L2_CTRL_CLASS_M2M_AUDIO media: uapi: Add audio rate controls support media: uapi: Declare interface types for Audio media: uapi: Add an entity type for audio resampler media: vivid: add fixed point test controls media: imx-asrc: Add memory to memory driver media: vim2m-audio: add virtual driver for audio memory to memory
.../media/mediactl/media-types.rst | 11 + .../userspace-api/media/v4l/buffer.rst | 6 + .../userspace-api/media/v4l/common.rst | 1 + .../media/v4l/dev-audio-mem2mem.rst | 71 + .../userspace-api/media/v4l/devices.rst | 1 + .../media/v4l/ext-ctrls-audio-m2m.rst | 59 + .../userspace-api/media/v4l/pixfmt-audio.rst | 100 ++ .../userspace-api/media/v4l/pixfmt.rst | 1 + .../media/v4l/vidioc-enum-fmt.rst | 2 + .../media/v4l/vidioc-g-ext-ctrls.rst | 4 + .../userspace-api/media/v4l/vidioc-g-fmt.rst | 4 + .../media/v4l/vidioc-querycap.rst | 3 + .../media/v4l/vidioc-queryctrl.rst | 11 +- .../media/videodev2.h.rst.exceptions | 3 + MAINTAINERS | 17 + .../media/common/videobuf2/videobuf2-v4l2.c | 4 + drivers/media/platform/nxp/Kconfig | 13 + drivers/media/platform/nxp/Makefile | 1 + drivers/media/platform/nxp/imx-asrc.c | 1256 +++++++++++++++++ drivers/media/test-drivers/Kconfig | 10 + drivers/media/test-drivers/Makefile | 1 + drivers/media/test-drivers/vim2m-audio.c | 793 +++++++++++ drivers/media/test-drivers/vivid/vivid-core.h | 2 + .../media/test-drivers/vivid/vivid-ctrls.c | 26 + drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 9 + drivers/media/v4l2-core/v4l2-ctrls-api.c | 1 + drivers/media/v4l2-core/v4l2-ctrls-core.c | 93 +- drivers/media/v4l2-core/v4l2-ctrls-defs.c | 10 + drivers/media/v4l2-core/v4l2-dev.c | 21 + drivers/media/v4l2-core/v4l2-ioctl.c | 66 + drivers/media/v4l2-core/v4l2-mem2mem.c | 13 +- include/media/v4l2-ctrls.h | 13 +- include/media/v4l2-dev.h | 2 + include/media/v4l2-ioctl.h | 34 + .../fsl => include/sound}/fsl_asrc_common.h | 60 + include/uapi/linux/media.h | 2 + include/uapi/linux/v4l2-controls.h | 9 + include/uapi/linux/videodev2.h | 50 +- sound/soc/fsl/fsl_asrc.c | 144 ++ sound/soc/fsl/fsl_asrc.h | 4 +- sound/soc/fsl/fsl_asrc_dma.c | 2 +- sound/soc/fsl/fsl_easrc.c | 233 +++ sound/soc/fsl/fsl_easrc.h | 6 +- 43 files changed, 3145 insertions(+), 27 deletions(-) create mode 100644 Documentation/userspace-api/media/v4l/dev-audio-mem2mem.rst create mode 100644 Documentation/userspace-api/media/v4l/ext-ctrls-audio-m2m.rst create mode 100644 Documentation/userspace-api/media/v4l/pixfmt-audio.rst create mode 100644 drivers/media/platform/nxp/imx-asrc.c create mode 100644 drivers/media/test-drivers/vim2m-audio.c rename {sound/soc/fsl => include/sound}/fsl_asrc_common.h (60%)
-- 2.34.1