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Date: Mon, 19 Feb 2024 12:27:18 +0200 From: Mathias Nyman <mathias.nyman@...ux.intel.com> To: Greg KH <gregkh@...uxfoundation.org>, Wesley Cheng <quic_wcheng@...cinc.com> Cc: 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, Thinh.Nguyen@...opsys.com, broonie@...nel.org, bgoswami@...cinc.com, tiwai@...e.com, robh+dt@...nel.org, konrad.dybcio@...aro.org, 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 v17 00/51] Introduce QC USB SND audio offloading support On 17.2.2024 17.25, Greg KH wrote: > On Fri, Feb 16, 2024 at 04:09:26PM -0800, 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 > > I've applied patches 1-10 and the 2 dts changes here, as those all had > acks from the relevant maintainers already. > Patch 10/10 is based on an old POC patch by me, but it's heavily modified. It looks like it does a few minor things that are not optimal, like extra spinlock/unlock, and wait_for_completion_timeout() with magical timeout value. I haven't tested this version, but I guess any fixes or cleanups can be done later on top of it. Thanks Mathias
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