Messages in this thread |  | | Date | Sat, 24 Dec 2022 00:49:14 -0800 | Subject | Re: [RFC PATCH 00/14] Introduce QC USB SND audio offloading support | From | Wesley Cheng <> |
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Hi Greg,
On 12/23/2022 10:45 PM, Greg KH wrote: > On Fri, Dec 23, 2022 at 03:31:46PM -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 >> >> 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 > > This looks to duplicate a bunch of the same things that a number of > different google developers have posted recently. Please work with them > to come up with a unified set of patches that you all can agree with, > AND get them to sign off on the changes before resubmitting them. > > This uncoordinated drip of patches from different people doing the same > thing is almost impossible to review from our side, as I'm sure you can > imagine.
I saw some of the Google patchsets submitted awhile back, but didn't really get a chance to look at them in detail. Let me reach out to Albert Wang to see if we can come to a solution that works for both implementations.
From the looks of it (at least from the XHCI HCD changes), it seems that a different set of resources is required for the Google implementation to work. I'll need to ask for a bit more details before I can comment further...
> > That being said, thank you finally for at least submitting all of the > needed changes together as one patch set. That's a first, and something > we had been asking for for years. > > Have a good holiday break,
Thanks for the quick in-depth review, and the feedback. Gives me some more things to think about improving over the break :). Happy holidays!
Thanks Wesley Cheng
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