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Date: Fri, 29 Mar 2024 16:28:49 -0700
From: Wesley Cheng <quic_wcheng@...cinc.com>
To: <srinivas.kandagatla@...aro.org>, <mathias.nyman@...el.com>,
<perex@...ex.cz>, <conor+dt@...nel.org>, <corbet@....net>,
<lgirdwood@...il.com>, <andersson@...nel.org>,
<krzysztof.kozlowski+dt@...aro.org>, <gregkh@...uxfoundation.org>,
<Thinh.Nguyen@...opsys.com>, <broonie@...nel.org>,
<bgoswami@...cinc.com>, <tiwai@...e.com>, <robh+dt@...nel.org>,
<konrad.dybcio@...aro.org>
CC: <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
<linux-sound@...r.kernel.org>, <linux-usb@...r.kernel.org>,
<linux-arm-msm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
<alsa-devel@...a-project.org>
Subject: Re: [PATCH v18 00/41] Introduce QC USB SND audio offloading support
Hi,
On 2/27/2024 5:35 PM, Wesley Cheng wrote:
> 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 v18:
> - Rebased to usb-next, which merged in part of the series. Removed these patches.
> - Reworked Kconfigs for the ASoC USB related components from QCOM Q6DSP drivers
> to keep dependencies in place for SoC USB and USB SND.
> - Removed the repurposing of the stop ep sync API into existing XHCI operations.
> This will be solely used by the XHCI sideband for now.
>
Wanted to give a friendly ping to see if there were any more
concerns/feedback about this series before I submit a new revision that
rebases to the latest kernel codebase?
Thanks
Wesley Cheng
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