[v9,00/34] Introduce QC USB SND audio offloading support

  Several Qualcomm based chipsets can support USB audio offloading to a
dedicated audio DSP, which can take over issuing transfers to the USB
host controller.  The intention is to reduce the load on the main
processors in the SoC, and allow them to be placed into lower power modes.
There are several parts to this design:
  1. Adding ASoC binding layer
  2. Create a USB backend for Q6DSP
  3. Introduce XHCI interrupter support
  4. Create vendor ops for the USB SND driver

      USB                          |            ASoC
--------------------------------------------------------------------
                                   |  _________________________
                                   | |sm8250 platform card     |
                                   | |_________________________|
                                   |         |           |
                                   |      ___V____   ____V____
                                   |     |Q6USB   | |Q6AFE    |  
                                   |     |"codec" | |"cpu"    |
                                   |     |________| |_________|
                                   |         ^  ^        ^
                                   |         |  |________|
                                   |      ___V____    |
                                   |     |SOC-USB |   |
   ________       ________               |        |   |
  |USB SND |<--->|QC offld|<------------>|________|   |
  |(card.c)|     |        |<----------                |
  |________|     |________|___     | |                |
      ^               ^       |    | |    ____________V_________
      |               |       |    | |   |APR/GLINK             |
   __ V_______________V_____  |    | |   |______________________|
  |USB SND (endpoint.c)     | |    | |              ^
  |_________________________| |    | |              |
              ^               |    | |   ___________V___________
              |               |    | |->|audio DSP              |
   ___________V_____________  |    |    |_______________________|
  |XHCI HCD                 |<-    |
  |_________________________|      |


Adding ASoC binding layer:
soc-usb: Intention is to treat a USB port similar to a headphone jack.
The port is always present on the device, but cable/pin status can be
enabled/disabled.  Expose mechanisms for USB backend ASoC drivers to
communicate with USB SND.

Create a USB backend for Q6DSP:
q6usb: Basic backend driver that will be responsible for maintaining the
resources needed to initiate a playback stream using the Q6DSP.  Will
be the entity that checks to make sure the connected USB audio device
supports the requested PCM format.  If it does not, the PCM open call will
fail, and userpsace ALSA can take action accordingly.

Introduce XHCI interrupter support:
XHCI HCD supports multiple interrupters, which allows for events to be routed
to different event rings.  This is determined by "Interrupter Target" field
specified in Section "6.4.1.1 Normal TRB" of the XHCI specification.

Events in the offloading case will be routed to an event ring that is assigned
to the audio DSP.

Create vendor ops for the USB SND driver:
qc_audio_offload: This particular driver has several components associated
with it:
- QMI stream request handler
- XHCI interrupter and resource management
- audio DSP memory management

When the audio DSP wants to enable a playback stream, the request is first
received by the ASoC platform sound card.  Depending on the selected route,
ASoC will bring up the individual DAIs in the path.  The Q6USB backend DAI
will send an AFE port start command (with enabling the USB playback path), and
the audio DSP will handle the request accordingly.

Part of the AFE USB port start handling will have an exchange of control
messages using the QMI protocol.  The qc_audio_offload driver will populate the
buffer information:
- Event ring base address
- EP transfer ring base address

and pass it along to the audio DSP.  All endpoint management will now be handed
over to the DSP, and the main processor is not involved in transfers.

Overall, implementing this feature will still expose separate sound card and PCM
devices for both the platorm card and USB audio device:
 0 [SM8250MTPWCD938]: sm8250 - SM8250-MTP-WCD9380-WSA8810-VA-D
                      SM8250-MTP-WCD9380-WSA8810-VA-DMIC
 1 [Audio          ]: USB-Audio - USB Audio
                      Generic USB Audio at usb-xhci-hcd.1.auto-1.4, high speed

This is to ensure that userspace ALSA entities can decide which route to take
when executing the audio playback.  In the above, if card#1 is selected, then
USB audio data will take the legacy path over the USB PCM drivers, etc...

This feature was validated using:
- tinymix: set/enable the multimedia path to route to USB backend
- tinyplay: issue playback on platform card

Changelog
--------------------------------------------
Changes in v9:
- Fixed the dt binding check issue with regards to num-hc-interrupters.

Changes in v8:
- Cleaned up snd_soc_usb_find_priv_data() based on Mark's feedback.  Removed some of
the duplicate looping code that was present on previous patches.  Also renamed the API.
- Integrated Mathias' suggestions on his new sideband changes:
https://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git/log/?h=feature_interrupters
- Addressed some of Mathias' fixme tags, such as:
 - Resetting transfer ring dequeue/enqueue pointers
 - Issuing stop endpoint command during ep removal
 - Reset ERDP properly to first segment ring during interrupter removal. (this is currently
   just being cleared to 0, but should be pointing to a valid segment if controller is still
   running.

Changes in v7:
- Fixed dt check error for q6usb bindings
- Updated q6usb property from qcom,usb-audio-intr-num --> qcom,usb-audio-intr-idx
- Removed separate DWC3 HC interrupters num property, and place limits to XHCI one.
- Modified xhci_ring_to_sgtable() to use assigned IOVA/DMA address to fetch pages, as
it is not ensured event ring allocated is always done in the vmalloc range.

Changes in v6:
- Fixed limits and description on several DT bindings (XHCI and Q6USB)
- Fixed patch subjects to follow other ALSA/ASoC notations.

USB SND
- Addressed devices which expose multiple audio (UAC) interfaces.  These devices will
create a single USB sound card with multiple audio streams, and receive multiple
interface probe routines.  QC offload was not properly considering cases with multiple
probe calls.
- Renamed offload module name and kconfig to fit within the SND domain.
- Renamed attach/detach endpoint API to keep the hw_params notation.

Changes in v5:
- Removed some unnescessary files that were included
- Fixed some typos mentioned
- Addressed dt-binding issues and added hc-interrupters definition to usb-xhci.yaml

XHCI:
- Moved secondary skip events API to xhci-ring and updated implementation
   - Utilized existing XHCI APIs, such as inc_deq and xhci_update_erst_dequeue()

USB SND
- Renamed and reworked the APIs in "sound: usb: Export USB SND APIs for modules" patch to
include suggestions to utilize snd_usb_hw_params/free and to avoid generic naming.
- Added a resume_cb() op for completion sake.
- Addressed some locking concerns with regards to when registering for platform hooks.
- Added routine to disconnect all offloaded devices during module unbind.

ASoC
- Replaced individual PCM parameter arguments in snd_soc_usb_connect() with new
snd_soc_usb_device structure to pass along PCM info.
- Modified snd_jack set report to notify HEADPHONE event, as we do not support record path.

Changes in v4:
- Rebased to xhci/for-usb-next
- Addressed some dt-bindings comments

XHCI:
- Pulled in latest changes from Mathias' feature_interrupters branch:
https://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git/log/?h=feature_interrupters

- Fixed commit text and signage for the XHCI sideband/interrupter related changes
- Added some logic to address the FIXME tags mentioned throughout the commits, such
as handling multi segment rings and building the SGT, locking concerns, and ep
cleanup operations.
- Removed some fixme tags for conditions that may not be needed/addressed.
- Repurposed the new endpoint stop sync API to be utilized in other places.
- Fixed potential compile issue if XHCI sideband config is not defined.

ASoC:
- Added sound jack control into the Q6USB driver.  Allows for userpsace to know when
an offload capable device is connected.

USB SND:
- Avoided exporting _snd_pcm_hw_param_set based on Takashi's recommendation.
- Split USB QMI packet header definitions into a separate commit.  This is used to
properly allow the QMI interface driver to parse and route QMI packets accordingly
- Added a "depends on" entry when enabling QC audio offload to avoid compile time
issues.

Changes in v3:
- Changed prefix from RFC to PATCH
- Rebased entire series to usb-next
- Updated copyright years

XHCI:
- Rebased changes on top of XHCI changes merged into usb-next, and only added
changes that were still under discussion.
- Added change to read in the "num-hc-interrupters" device property.

ASoC:
- qusb6 USB backend
  - Incorporated suggestions to fetch iommu information with existing APIs
  - Added two new sound kcontrols to fetch offload status and offload device
    selection.
    - offload status - will return the card and pcm device in use
        tinymix -D 0 get 1 --> 1, 0 (offload in progress on card#1 pcm#0)

    - device selection - set the card and pcm device to enable offload on. Ex.:
        tinymix -D 0 set 1 2 0  --> sets offload on card#2 pcm#0
                                    (this should be the USB card)

USB SND:
- Fixed up some locking related concerns for registering platform ops.
   - Moved callbacks under the register_mutex, so that 
- Modified APIs to properly pass more information about the USB SND device, so
that the Q6USB backend can build a device list/map, in order to monitor offload
status and device selection.

Changes in v2:

XHCI:
- Replaced XHCI and HCD changes with Mathias' XHCI interrupter changes
in his tree:
https://git.kernel.org/pub/scm/linux/kernel/git/mnyman/xhci.git/log/?h=feature_interrupters

Adjustments made to Mathias' changes:
  - Created xhci-intr.h to export/expose interrupter APIs versus exposing xhci.h.
    Moved dependent structures to this file as well. (so clients can parse out
    information from "struct xhci_interrupter")
  - Added some basic locking when requesting interrupters.
  - Fixed up some sanity checks.
  - Removed clearing of the ERSTBA during freeing of the interrupter. (pending
    issue where SMMU fault occurs if DMA addr returned is 64b - TODO)

- Clean up pending events in the XHCI secondary interrupter.  While testing USB
bus suspend, it was seen that on bus resume, the xHCI HC would run into a command
timeout.
- Added offloading APIs to xHCI to fetch transfer and event ring information.

ASoC:
- Modified soc-usb to allow for multiple USB port additions.  For this to work,
the USB offload driver has to have a reference to the USB backend by adding
a "usb-soc-be" DT entry to the device saved into XHCI sysdev.
- Created separate dt-bindings for defining USB_RX port.
- Increased APR timeout to accommodate the situation where the AFE port start
command could be delayed due to having to issue a USB bus resume while
handling the QMI stream start command.

USB SND:
- Added a platform ops during usb_audio_suspend().  This allows for the USB
offload driver to halt the audio stream when system enters PM suspend.  This
ensures the audio DSP is not issuing transfers on the USB bus.
- Do not override platform ops if they are already populated.
- Introduce a shared status variable between the USB offload and USB SND layers,
to ensure that only one path is active at a time.  If the USB bus is occupied,
then userspace is notified that the path is busy.

Mathias Nyman (4):
  xhci: split free interrupter into separate remove and free parts
  xhci: add support to allocate several interrupters
  xhci: add helper to stop endpoint and wait for completion
  xhci: sideband: add initial api to register a sideband entity

Wesley Cheng (30):
  usb: host: xhci-mem: Cleanup pending secondary event ring events
  usb: host: xhci-mem: Allow for interrupter clients to choose specific
    index
  ASoC: Add SOC USB APIs for adding an USB backend
  ASoC: dt-bindings: qcom,q6dsp-lpass-ports: Add USB_RX port
  ASoC: qcom: qdsp6: Introduce USB AFE port to q6dsp
  ASoC: qdsp6: q6afe: Increase APR timeout
  ASoC: qcom: qdsp6: Add USB backend ASoC driver for Q6
  ALSA: usb-audio: Introduce USB SND platform op callbacks
  ALSA: usb-audio: Export USB SND APIs for modules
  dt-bindings: usb: xhci: Add num-hc-interrupters definition
  dt-bindings: usb: dwc3: Limit num-hc-interrupters definition
  usb: dwc3: Specify maximum number of XHCI interrupters
  usb: host: xhci-plat: Set XHCI max interrupters if property is present
  ALSA: usb-audio: qcom: Add USB QMI definitions
  ALSA: usb-audio: qcom: Introduce QC USB SND offloading support
  ALSA: usb-audio: Check for support for requested audio format
  ASoC: usb: Add PCM format check API for USB backend
  ASoC: qcom: qdsp6: Ensure PCM format is supported by USB audio device
  ALSA: usb-audio: Prevent starting of audio stream if in use
  ASoC: dt-bindings: Add Q6USB backend
  ASoC: dt-bindings: Update example for enabling USB offload on SM8250
  ASoC: qcom: qdsp6: q6afe: Split USB AFE dev_token param into separate
    API
  ALSA: usb-audio: qcom: Populate PCM and USB chip information
  ASoC: qcom: qdsp6: Add support to track available USB PCM devices
  ASoC: qcom: qdsp6: Add SND kcontrol to select offload device
  ASoC: qcom: qdsp6: Add SND kcontrol for fetching offload status
  ASoC: qcom: qdsp6: Add headphone jack for offload connection status
  ALSA: usb-audio: qcom: Use card and PCM index from QMI request
  ALSA: usb-audio: Allow for rediscovery of connected USB SND devices
  ASoC: usb: Rediscover USB SND devices on USB port add

 .../devicetree/bindings/sound/qcom,q6usb.yaml |   55 +
 .../bindings/sound/qcom,sm8250.yaml           |   15 +
 .../devicetree/bindings/usb/snps,dwc3.yaml    |    4 +
 .../devicetree/bindings/usb/usb-xhci.yaml     |    6 +
 drivers/usb/dwc3/core.c                       |   12 +
 drivers/usb/dwc3/core.h                       |    2 +
 drivers/usb/dwc3/host.c                       |    5 +-
 drivers/usb/host/Kconfig                      |    9 +
 drivers/usb/host/Makefile                     |    4 +
 drivers/usb/host/xhci-debugfs.c               |    2 +-
 drivers/usb/host/xhci-mem.c                   |  136 +-
 drivers/usb/host/xhci-plat.c                  |    2 +
 drivers/usb/host/xhci-ring.c                  |   53 +-
 drivers/usb/host/xhci-sideband.c              |  372 ++++
 drivers/usb/host/xhci.c                       |  114 +-
 drivers/usb/host/xhci.h                       |   18 +-
 .../sound/qcom,q6dsp-lpass-ports.h            |    1 +
 include/linux/usb/xhci-sideband.h             |   67 +
 include/sound/q6usboffload.h                  |   20 +
 include/sound/soc-usb.h                       |   51 +
 sound/soc/Makefile                            |    2 +-
 sound/soc/qcom/Kconfig                        |    4 +
 sound/soc/qcom/qdsp6/Makefile                 |    1 +
 sound/soc/qcom/qdsp6/q6afe-dai.c              |   56 +
 sound/soc/qcom/qdsp6/q6afe.c                  |  206 +-
 sound/soc/qcom/qdsp6/q6afe.h                  |   36 +-
 sound/soc/qcom/qdsp6/q6dsp-lpass-ports.c      |   23 +
 sound/soc/qcom/qdsp6/q6dsp-lpass-ports.h      |    1 +
 sound/soc/qcom/qdsp6/q6routing.c              |    9 +
 sound/soc/qcom/qdsp6/q6usb.c                  |  450 ++++
 sound/soc/soc-usb.c                           |  201 ++
 sound/usb/Kconfig                             |   15 +
 sound/usb/Makefile                            |    2 +-
 sound/usb/card.c                              |  123 ++
 sound/usb/card.h                              |   23 +
 sound/usb/endpoint.c                          |    1 +
 sound/usb/helper.c                            |    1 +
 sound/usb/pcm.c                               |   94 +-
 sound/usb/pcm.h                               |   11 +
 sound/usb/qcom/Makefile                       |    2 +
 sound/usb/qcom/qc_audio_offload.c             | 1867 +++++++++++++++++
 sound/usb/qcom/usb_audio_qmi_v01.c            |  892 ++++++++
 sound/usb/qcom/usb_audio_qmi_v01.h            |  162 ++
 43 files changed, 5041 insertions(+), 89 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/sound/qcom,q6usb.yaml
 create mode 100644 drivers/usb/host/xhci-sideband.c
 create mode 100644 include/linux/usb/xhci-sideband.h
 create mode 100644 include/sound/q6usboffload.h
 create mode 100644 include/sound/soc-usb.h
 create mode 100644 sound/soc/qcom/qdsp6/q6usb.c
 create mode 100644 sound/soc/soc-usb.c
 create mode 100644 sound/usb/qcom/Makefile
 create mode 100644 sound/usb/qcom/qc_audio_offload.c
 create mode 100644 sound/usb/qcom/usb_audio_qmi_v01.c
 create mode 100644 sound/usb/qcom/usb_audio_qmi_v01.h
  

It's been a very long time since I reviewed earlier versions, and I am
still lost on terminology and concepts. The explanations below should
really be added as a .rst file in Documentation for reference, not just
as a cover letter.

> Several Qualcomm based chipsets can support USB audio offloading to a
> dedicated audio DSP, which can take over issuing transfers to the USB
> host controller.  The intention is to reduce the load on the main
> processors in the SoC, and allow them to be placed into lower power modes.
> There are several parts to this design:
>   1. Adding ASoC binding layer
>   2. Create a USB backend for Q6DSP

"backend" is a loaded terms for ASoC. Can you clarify which part of the
ascii art below is a 'backend'?

>   3. Introduce XHCI interrupter support
>   4. Create vendor ops for the USB SND driver
> 
>       USB                          |            ASoC
> --------------------------------------------------------------------
>                                    |  _________________________
>                                    | |sm8250 platform card     |
>                                    | |_________________________|
>                                    |         |           |
>                                    |      ___V____   ____V____
>                                    |     |Q6USB   | |Q6AFE    |  
>                                    |     |"codec" | |"cpu"    |
>                                    |     |________| |_________|
>                                    |         ^  ^        ^
>                                    |         |  |________|
>                                    |      ___V____    |
>                                    |     |SOC-USB |   |
>    ________       ________               |        |   |
>   |USB SND |<--->|QC offld|<------------>|________|   |
>   |(card.c)|     |        |<----------                |
>   |________|     |________|___     | |                |
>       ^               ^       |    | |    ____________V_________
>       |               |       |    | |   |APR/GLINK             |
>    __ V_______________V_____  |    | |   |______________________|
>   |USB SND (endpoint.c)     | |    | |              ^
>   |_________________________| |    | |              |
>               ^               |    | |   ___________V___________
>               |               |    | |->|audio DSP              |
>    ___________V_____________  |    |    |_______________________|
>   |XHCI HCD                 |<-    |
>   |_________________________|      |
> 
> 
> Adding ASoC binding layer:
> soc-usb: Intention is to treat a USB port similar to a headphone jack.

What is a 'port'? USB refers to "interfaces" and "endpoints". Is a
"port" a 1:1 mapping to "endpoint"?

Below I read "AFE port" so not sure what concepts refer to what.

> The port is always present on the device, but cable/pin status can be
> enabled/disabled.  Expose mechanisms for USB backend ASoC drivers to
> communicate with USB SND.
> 
> Create a USB backend for Q6DSP:
> q6usb: Basic backend driver that will be responsible for maintaining the

The asciiart above suggests that q6usb exposes a codec DAI - but the
backend dailink is created by the platform card?

> resources needed to initiate a playback stream using the Q6DSP.  Will

is capture supported? there's explicit references to "num_capture" in
following patches.

> be the entity that checks to make sure the connected USB audio device
> supports the requested PCM format.  If it does not, the PCM open call will
> fail, and userpsace ALSA can take action accordingly.
> 
> Introduce XHCI interrupter support:
> XHCI HCD supports multiple interrupters, which allows for events to be routed
> to different event rings.  This is determined by "Interrupter Target" field
> specified in Section "6.4.1.1 Normal TRB" of the XHCI specification.
> 
> Events in the offloading case will be routed to an event ring that is assigned
> to the audio DSP.
> 
> Create vendor ops for the USB SND driver:
> qc_audio_offload: This particular driver has several components associated
> with it:
> - QMI stream request handler
> - XHCI interrupter and resource management
> - audio DSP memory management
> 
> When the audio DSP wants to enable a playback stream, the request is first
> received by the ASoC platform sound card.  Depending on the selected route,
> ASoC will bring up the individual DAIs in the path.  The Q6USB backend DAI
> will send an AFE port start command (with enabling the USB playback path), and
> the audio DSP will handle the request accordingly.

what about capture, e.g. for a headset?

> Part of the AFE USB port start handling will have an exchange of control
> messages using the QMI protocol.  The qc_audio_offload driver will populate the
> buffer information:
> - Event ring base address
> - EP transfer ring base address
> 
> and pass it along to the audio DSP.  All endpoint management will now be handed
> over to the DSP, and the main processor is not involved in transfers.
> 
> Overall, implementing this feature will still expose separate sound card and PCM
> devices for both the platorm card and USB audio device:

typo: platform

>  0 [SM8250MTPWCD938]: sm8250 - SM8250-MTP-WCD9380-WSA8810-VA-D
>                       SM8250-MTP-WCD9380-WSA8810-VA-DMIC

How do you plan on exposing the USB PCM device?

The lines above are really cryptic, and with no USB reference in any of
the short/long card names it's not obvious that this card is different
from the no-offload case, is it?

>  1 [Audio          ]: USB-Audio - USB Audio
>                       Generic USB Audio at usb-xhci-hcd.1.auto-1.4, high speed

likewise some sort of qualifier would be useful to show that card 0 and
card 1 can target the same USB endpoints.

> This is to ensure that userspace ALSA entities can decide which route to take
> when executing the audio playback.  In the above, if card#1 is selected, then
> USB audio data will take the legacy path over the USB PCM drivers, etc...
> 
> This feature was validated using:
> - tinymix: set/enable the multimedia path to route to USB backend
> - tinyplay: issue playback on platform card
  

Hi Pierre,

On 10/17/2023 1:58 PM, Pierre-Louis Bossart wrote:
> It's been a very long time since I reviewed earlier versions, and I am
> still lost on terminology and concepts. The explanations below should
> really be added as a .rst file in Documentation for reference, not just
> as a cover letter.
> 

Thanks for the review!

Sure, maybe I can write a more comprehensive documentation that saves 
these details somewhere.  Will add a RST documentation for material 
where necessary.

>> Several Qualcomm based chipsets can support USB audio offloading to a
>> dedicated audio DSP, which can take over issuing transfers to the USB
>> host controller.  The intention is to reduce the load on the main
>> processors in the SoC, and allow them to be placed into lower power modes.
>> There are several parts to this design:
>>    1. Adding ASoC binding layer
>>    2. Create a USB backend for Q6DSP
> 
> "backend" is a loaded terms for ASoC. Can you clarify which part of the
> ascii art below is a 'backend'?
> 

This would be the Q6USB entity which is the DPCM backend for this 
particular audio path.

>>    3. Introduce XHCI interrupter support
>>    4. Create vendor ops for the USB SND driver
>>
>>        USB                          |            ASoC
>> --------------------------------------------------------------------
>>                                     |  _________________________
>>                                     | |sm8250 platform card     |
>>                                     | |_________________________|
>>                                     |         |           |
>>                                     |      ___V____   ____V____
>>                                     |     |Q6USB   | |Q6AFE    |
>>                                     |     |"codec" | |"cpu"    |
>>                                     |     |________| |_________|
>>                                     |         ^  ^        ^
>>                                     |         |  |________|
>>                                     |      ___V____    |
>>                                     |     |SOC-USB |   |
>>     ________       ________               |        |   |
>>    |USB SND |<--->|QC offld|<------------>|________|   |
>>    |(card.c)|     |        |<----------                |
>>    |________|     |________|___     | |                |
>>        ^               ^       |    | |    ____________V_________
>>        |               |       |    | |   |APR/GLINK             |
>>     __ V_______________V_____  |    | |   |______________________|
>>    |USB SND (endpoint.c)     | |    | |              ^
>>    |_________________________| |    | |              |
>>                ^               |    | |   ___________V___________
>>                |               |    | |->|audio DSP              |
>>     ___________V_____________  |    |    |_______________________|
>>    |XHCI HCD                 |<-    |
>>    |_________________________|      |
>>
>>
>> Adding ASoC binding layer:
>> soc-usb: Intention is to treat a USB port similar to a headphone jack.
> 
> What is a 'port'? USB refers to "interfaces" and "endpoints". Is a
> "port" a 1:1 mapping to "endpoint"?
> 
> Below I read "AFE port" so not sure what concepts refer to what.
> 

"Port" in this explanation refers to the USB port.  So the audio device 
connected.  You are right that a USB device can enumerate w/ multiple 
interfaces (ie UAC + HID + ...) so the closest relation to "port" is 
"interface."  It is not a 1:1 mapping w/ the number of endpoints exposed 
by a device.

"AFE port" is just something that has been termed from the audio DSP 
end, so that concept of port is not related to the port where USB 
devices are connected to.  This is something that is defined within the 
audio DSP.

>> The port is always present on the device, but cable/pin status can be
>> enabled/disabled.  Expose mechanisms for USB backend ASoC drivers to
>> communicate with USB SND.
>>
>> Create a USB backend for Q6DSP:
>> q6usb: Basic backend driver that will be responsible for maintaining the
> 
> The asciiart above suggests that q6usb exposes a codec DAI - but the
> backend dailink is created by the platform card?
> 

That is my understanding, at least.  The machine driver (sm8250.c) has 
an API that parses our DT node for the DAI relationships 
(qcom_snd_parse_of()), and seems to also create the dailinks.

>> resources needed to initiate a playback stream using the Q6DSP.  Will
> 
> is capture supported? there's explicit references to "num_capture" in
> following patches.
> 

We (QCOM) do not support capture at the moment, but the num_capture was 
added to the soc-usb driver, which is platform independent.  This is in 
case other vendors want to add this support, but have capture included 
as well.

>> be the entity that checks to make sure the connected USB audio device
>> supports the requested PCM format.  If it does not, the PCM open call will
>> fail, and userpsace ALSA can take action accordingly.
>>
>> Introduce XHCI interrupter support:
>> XHCI HCD supports multiple interrupters, which allows for events to be routed
>> to different event rings.  This is determined by "Interrupter Target" field
>> specified in Section "6.4.1.1 Normal TRB" of the XHCI specification.
>>
>> Events in the offloading case will be routed to an event ring that is assigned
>> to the audio DSP.
>>
>> Create vendor ops for the USB SND driver:
>> qc_audio_offload: This particular driver has several components associated
>> with it:
>> - QMI stream request handler
>> - XHCI interrupter and resource management
>> - audio DSP memory management
>>
>> When the audio DSP wants to enable a playback stream, the request is first
>> received by the ASoC platform sound card.  Depending on the selected route,
>> ASoC will bring up the individual DAIs in the path.  The Q6USB backend DAI
>> will send an AFE port start command (with enabling the USB playback path), and
>> the audio DSP will handle the request accordingly.
> 
> what about capture, e.g. for a headset?
> 

Not supported yet at the moment.

>> Part of the AFE USB port start handling will have an exchange of control
>> messages using the QMI protocol.  The qc_audio_offload driver will populate the
>> buffer information:
>> - Event ring base address
>> - EP transfer ring base address
>>
>> and pass it along to the audio DSP.  All endpoint management will now be handed
>> over to the DSP, and the main processor is not involved in transfers.
>>
>> Overall, implementing this feature will still expose separate sound card and PCM
>> devices for both the platorm card and USB audio device:
> 
> typo: platform
> 

Thanks, will fix this.

>>   0 [SM8250MTPWCD938]: sm8250 - SM8250-MTP-WCD9380-WSA8810-VA-D
>>                        SM8250-MTP-WCD9380-WSA8810-VA-DMIC
> 
> How do you plan on exposing the USB PCM device?
> 
> The lines above are really cryptic, and with no USB reference in any of
> the short/long card names it's not obvious that this card is different
> from the no-offload case, is it?
> 

In the end, since the offload case is handled by the audio DSP, it would 
have to go through the platform/machine sound card.  That is the sm8250 
device above.

>>   1 [Audio          ]: USB-Audio - USB Audio
>>                        Generic USB Audio at usb-xhci-hcd.1.auto-1.4, high speed
> 
> likewise some sort of qualifier would be useful to show that card 0 and
> card 1 can target the same USB endpoints.
> 

Do userspace entities look at this card string?  Assuming there is only 
one platform card, there are situations where maybe multiple USB audio 
devices are connected to the same USB root hub, so offloading can happen 
on any one of them (not at the same time).

Thanks
Wesley Cheng
  

On 10/17/23 19:25, Wesley Cheng wrote:
> Hi Pierre,
> 
> On 10/17/2023 1:58 PM, Pierre-Louis Bossart wrote:
>> It's been a very long time since I reviewed earlier versions, and I am
>> still lost on terminology and concepts. The explanations below should
>> really be added as a .rst file in Documentation for reference, not just
>> as a cover letter.
>>
> 
> Thanks for the review!
> 
> Sure, maybe I can write a more comprehensive documentation that saves
> these details somewhere.  Will add a RST documentation for material
> where necessary.
> 
>>> Several Qualcomm based chipsets can support USB audio offloading to a
>>> dedicated audio DSP, which can take over issuing transfers to the USB
>>> host controller.  The intention is to reduce the load on the main
>>> processors in the SoC, and allow them to be placed into lower power
>>> modes.
>>> There are several parts to this design:
>>>    1. Adding ASoC binding layer
>>>    2. Create a USB backend for Q6DSP
>>
>> "backend" is a loaded terms for ASoC. Can you clarify which part of the
>> ascii art below is a 'backend'?
>>
> 
> This would be the Q6USB entity which is the DPCM backend for this
> particular audio path.

DPCM is about dailinks. Technically the q6usb entity is a codec dai
which is part of a DPCM backend dailink.
> 
>>>    3. Introduce XHCI interrupter support
>>>    4. Create vendor ops for the USB SND driver
>>>
>>>        USB                          |            ASoC
>>> --------------------------------------------------------------------
>>>                                     |  _________________________
>>>                                     | |sm8250 platform card     |
>>>                                     | |_________________________|
>>>                                     |         |           |
>>>                                     |      ___V____   ____V____
>>>                                     |     |Q6USB   | |Q6AFE    |
>>>                                     |     |"codec" | |"cpu"    |
>>>                                     |     |________| |_________|
>>>                                     |         ^  ^        ^
>>>                                     |         |  |________|
>>>                                     |      ___V____    |
>>>                                     |     |SOC-USB |   |
>>>     ________       ________               |        |   |
>>>    |USB SND |<--->|QC offld|<------------>|________|   |
>>>    |(card.c)|     |        |<----------                |
>>>    |________|     |________|___     | |                |
>>>        ^               ^       |    | |    ____________V_________
>>>        |               |       |    | |   |APR/GLINK             |
>>>     __ V_______________V_____  |    | |   |______________________|
>>>    |USB SND (endpoint.c)     | |    | |              ^
>>>    |_________________________| |    | |              |
>>>                ^               |    | |   ___________V___________
>>>                |               |    | |->|audio DSP              |
>>>     ___________V_____________  |    |    |_______________________|
>>>    |XHCI HCD                 |<-    |
>>>    |_________________________|      |
>>>
>>>
>>> Adding ASoC binding layer:
>>> soc-usb: Intention is to treat a USB port similar to a headphone jack.
>>
>> What is a 'port'? USB refers to "interfaces" and "endpoints". Is a
>> "port" a 1:1 mapping to "endpoint"?
>>
>> Below I read "AFE port" so not sure what concepts refer to what.
>>
> 
> "Port" in this explanation refers to the USB port.  So the audio device
> connected.  You are right that a USB device can enumerate w/ multiple
> interfaces (ie UAC + HID + ...) so the closest relation to "port" is
> "interface."  It is not a 1:1 mapping w/ the number of endpoints exposed
> by a device.
> 
> "AFE port" is just something that has been termed from the audio DSP
> end, so that concept of port is not related to the port where USB
> devices are connected to.  This is something that is defined within the
> audio DSP.

Wow. So there's a "USB port" and "AFE port". I would recommend avoiding
the same term for completely different concepts. Why not use "USB device"?

>>>   0 [SM8250MTPWCD938]: sm8250 - SM8250-MTP-WCD9380-WSA8810-VA-D
>>>                        SM8250-MTP-WCD9380-WSA8810-VA-DMIC
>>
>> How do you plan on exposing the USB PCM device?
>>
>> The lines above are really cryptic, and with no USB reference in any of
>> the short/long card names it's not obvious that this card is different
>> from the no-offload case, is it?
>>
> 
> In the end, since the offload case is handled by the audio DSP, it would
> have to go through the platform/machine sound card.  That is the sm8250
> device above.
> 
>>>   1 [Audio          ]: USB-Audio - USB Audio
>>>                        Generic USB Audio at usb-xhci-hcd.1.auto-1.4,
>>> high speed
>>
>> likewise some sort of qualifier would be useful to show that card 0 and
>> card 1 can target the same USB endpoints.
>>
> 
> Do userspace entities look at this card string?  Assuming there is only
> one platform card, there are situations where maybe multiple USB audio
> devices are connected to the same USB root hub, so offloading can happen
> on any one of them (not at the same time).

Jaroslav cares, as measured by the changes over the years to make the
card names more self-explanatory.

I really don't see anything in the SM8250MTPWCD938 card name that would
hint at the support of USB. If it's not in the card string, maybe this
can be added in the component string as well (amixer -Dhw:0 info). The
point is that userspace should not have to maintain an 'accept-list' of
card names but have the means to check the USB offload capability with a
vendor-neutral convention.
  

Hi Pierre,

On 10/18/2023 6:54 AM, Pierre-Louis Bossart wrote:
> 
> 
> On 10/17/23 19:25, Wesley Cheng wrote:
>> Hi Pierre,
>>
>> On 10/17/2023 1:58 PM, Pierre-Louis Bossart wrote:
>>> It's been a very long time since I reviewed earlier versions, and I am
>>> still lost on terminology and concepts. The explanations below should
>>> really be added as a .rst file in Documentation for reference, not just
>>> as a cover letter.
>>>
>>
>> Thanks for the review!
>>
>> Sure, maybe I can write a more comprehensive documentation that saves
>> these details somewhere.  Will add a RST documentation for material
>> where necessary.
>>
>>>> Several Qualcomm based chipsets can support USB audio offloading to a
>>>> dedicated audio DSP, which can take over issuing transfers to the USB
>>>> host controller.  The intention is to reduce the load on the main
>>>> processors in the SoC, and allow them to be placed into lower power
>>>> modes.
>>>> There are several parts to this design:
>>>>     1. Adding ASoC binding layer
>>>>     2. Create a USB backend for Q6DSP
>>>
>>> "backend" is a loaded terms for ASoC. Can you clarify which part of the
>>> ascii art below is a 'backend'?
>>>
>>
>> This would be the Q6USB entity which is the DPCM backend for this
>> particular audio path.
> 
> DPCM is about dailinks. Technically the q6usb entity is a codec dai
> which is part of a DPCM backend dailink.
>>
>>>>     3. Introduce XHCI interrupter support
>>>>     4. Create vendor ops for the USB SND driver
>>>>
>>>>         USB                          |            ASoC
>>>> --------------------------------------------------------------------
>>>>                                      |  _________________________
>>>>                                      | |sm8250 platform card     |
>>>>                                      | |_________________________|
>>>>                                      |         |           |
>>>>                                      |      ___V____   ____V____
>>>>                                      |     |Q6USB   | |Q6AFE    |
>>>>                                      |     |"codec" | |"cpu"    |
>>>>                                      |     |________| |_________|
>>>>                                      |         ^  ^        ^
>>>>                                      |         |  |________|
>>>>                                      |      ___V____    |
>>>>                                      |     |SOC-USB |   |
>>>>      ________       ________               |        |   |
>>>>     |USB SND |<--->|QC offld|<------------>|________|   |
>>>>     |(card.c)|     |        |<----------                |
>>>>     |________|     |________|___     | |                |
>>>>         ^               ^       |    | |    ____________V_________
>>>>         |               |       |    | |   |APR/GLINK             |
>>>>      __ V_______________V_____  |    | |   |______________________|
>>>>     |USB SND (endpoint.c)     | |    | |              ^
>>>>     |_________________________| |    | |              |
>>>>                 ^               |    | |   ___________V___________
>>>>                 |               |    | |->|audio DSP              |
>>>>      ___________V_____________  |    |    |_______________________|
>>>>     |XHCI HCD                 |<-    |
>>>>     |_________________________|      |
>>>>
>>>>
>>>> Adding ASoC binding layer:
>>>> soc-usb: Intention is to treat a USB port similar to a headphone jack.
>>>
>>> What is a 'port'? USB refers to "interfaces" and "endpoints". Is a
>>> "port" a 1:1 mapping to "endpoint"?
>>>
>>> Below I read "AFE port" so not sure what concepts refer to what.
>>>
>>
>> "Port" in this explanation refers to the USB port.  So the audio device
>> connected.  You are right that a USB device can enumerate w/ multiple
>> interfaces (ie UAC + HID + ...) so the closest relation to "port" is
>> "interface."  It is not a 1:1 mapping w/ the number of endpoints exposed
>> by a device.
>>
>> "AFE port" is just something that has been termed from the audio DSP
>> end, so that concept of port is not related to the port where USB
>> devices are connected to.  This is something that is defined within the
>> audio DSP.
> 
> Wow. So there's a "USB port" and "AFE port". I would recommend avoiding
> the same term for completely different concepts. Why not use "USB device"?
> 

I think maybe USB interface is probably the most acceptable, since even 
at the USB snd level, they work based on usb_interface, not on the udev 
(USB device) itself.

>>>>    0 [SM8250MTPWCD938]: sm8250 - SM8250-MTP-WCD9380-WSA8810-VA-D
>>>>                         SM8250-MTP-WCD9380-WSA8810-VA-DMIC
>>>
>>> How do you plan on exposing the USB PCM device?
>>>
>>> The lines above are really cryptic, and with no USB reference in any of
>>> the short/long card names it's not obvious that this card is different
>>> from the no-offload case, is it?
>>>
>>
>> In the end, since the offload case is handled by the audio DSP, it would
>> have to go through the platform/machine sound card.  That is the sm8250
>> device above.
>>
>>>>    1 [Audio          ]: USB-Audio - USB Audio
>>>>                         Generic USB Audio at usb-xhci-hcd.1.auto-1.4,
>>>> high speed
>>>
>>> likewise some sort of qualifier would be useful to show that card 0 and
>>> card 1 can target the same USB endpoints.
>>>
>>
>> Do userspace entities look at this card string?  Assuming there is only
>> one platform card, there are situations where maybe multiple USB audio
>> devices are connected to the same USB root hub, so offloading can happen
>> on any one of them (not at the same time).
> 
> Jaroslav cares, as measured by the changes over the years to make the
> card names more self-explanatory.
> 
> I really don't see anything in the SM8250MTPWCD938 card name that would
> hint at the support of USB. If it's not in the card string, maybe this
> can be added in the component string as well (amixer -Dhw:0 info). The
> point is that userspace should not have to maintain an 'accept-list' of
> card names but have the means to check the USB offload capability with a
> vendor-neutral convention.

I'll take a look at adding it into the components string.  At least in 
that case, we'd be able to dynamically modify to say if USB offload is 
supported or not based on the child entries/paths that are defined in 
the DT node.

Thanks
Wesley Cheng