| Message ID | 20221223233200.26089-1-quic_wcheng@quicinc.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | Introduce QC USB SND audio offloading support | expand |
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
On Sat, Dec 24, 2022 at 07:45:38AM +0100, Greg KH wrote: > On Fri, Dec 23, 2022 at 03:31:46PM -0800, Wesley Cheng wrote: > > 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 > 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 have to say this is the first I've heard of any such patches other than from the Qualcomm people and I can't immediately see anything that was on the list either, though I might be missing something since I don't have the subject or anything. If other people send things again it's probably good to suggest they copy in audio people and lists.
On 12/23/22 17:31, 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. It would be nice to clarify what you want to offload a) audio data transfers for isoc ports b) control for e.g. volume settings (those go to endpoint 0 IIRC) c) Both? This has a lot of implications on the design. ASoC/DPCM is mainly intended for audio data transfers, control is a separate problem with configurations handled with register settings or bus-specific commands. > 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... You would still need some sort of mutual exclusion to make sure the isoc endpoints are not used concurrently by the two cards. Relying on userspace intelligence to enforce that exclusion is not safe IMHO. Intel looked at this sort of offload support a while ago and our directions were very different - for a variety of reasons USB offload is enabled on Windows platforms but remains a TODO for Linux. Rather than having two cards, you could have a single card and addition subdevices that expose the paths through the DSP. The benefits were that there was a single set of controls that userspace needed to know about, and volume settings were the same no matter which path you used (legacy or DSP-optimized paths). That's consistent with the directions to use 'Deep Buffer' PCM paths for local playback, it's the same idea of reducing power consumption with optimized routing. Another point is that there may be cases where the DSP paths are not available if the DSP memory and MCPS budget is exceeded. In those cases, the DSP parts needs the ability to notify userspace that the legacy path should be used. Another case to handle is that some USB devices can handle way more data than DSPs can chew, for example Pro audio boxes that can deal with 8ch 192kHz will typically use the legacy paths. Some also handle specific formats such as DSD over PCM. So it's quite likely that PCM devices for card0 and card1 above do NOT expose support for the same formats, or put differently that only a subset of the USB device capabilities are handled through the DSP. And last, power optimizations with DSPs typically come from additional latency helping put the SoC in low-power modes. That's not necessarily ideal for all usages, e.g. for music recording and mixing I am not convinced the DSP path would help at all. > 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 1/4/2023 3:19 PM, Pierre-Louis Bossart wrote: > > > On 12/23/22 17:31, 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. > > It would be nice to clarify what you want to offload > a) audio data transfers for isoc ports > b) control for e.g. volume settings (those go to endpoint 0 IIRC) > c) Both? > Thanks for sharing your experience, and inputs! It would be the audio related endpoints only, so ISOC and potentially feedback ep. > This has a lot of implications on the design. ASoC/DPCM is mainly > intended for audio data transfers, control is a separate problem with > configurations handled with register settings or bus-specific commands. > Control would still be handled by the main processor. >> 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... > > You would still need some sort of mutual exclusion to make sure the isoc > endpoints are not used concurrently by the two cards. Relying on > userspace intelligence to enforce that exclusion is not safe IMHO. > Sure, I think we can make the USB card as being used if the offloading path is currently being enabled. Kernel could return an error to userspace when this situation happens. > Intel looked at this sort of offload support a while ago and our > directions were very different - for a variety of reasons USB offload is > enabled on Windows platforms but remains a TODO for Linux. Rather than > having two cards, you could have a single card and addition subdevices > that expose the paths through the DSP. The benefits were that there was > a single set of controls that userspace needed to know about, and volume > settings were the same no matter which path you used (legacy or > DSP-optimized paths). That's consistent with the directions to use 'Deep > Buffer' PCM paths for local playback, it's the same idea of reducing > power consumption with optimized routing. > Volume control would still be done through the legacy path as mentioned above. For example, if a USB headset w/ a HID interface exposed (for volume control) was connected, those HID events would be routed to userspace to adjust volume accordingly on the main processor. (although you're right about having separate controls still present - one for the ASoC card and another for USB card) > Another point is that there may be cases where the DSP paths are not > available if the DSP memory and MCPS budget is exceeded. In those cases, > the DSP parts needs the ability to notify userspace that the legacy path > should be used. If we ran into this scenario, the audio DSP AFE port start command would fail, and this would be propagated to the userspace entity. It could then potentially re-route to the legacy/non-offload path. > > Another case to handle is that some USB devices can handle way more data > than DSPs can chew, for example Pro audio boxes that can deal with 8ch > 192kHz will typically use the legacy paths. Some also handle specific > formats such as DSD over PCM. So it's quite likely that PCM devices for > card0 and card1 above do NOT expose support for the same formats, or put > differently that only a subset of the USB device capabilities are > handled through the DSP. Same as the above. We have programmed the USB backend to support the profiles that the audio DSP can handle. I assume if there was any other request, the userspace entity would fail the PCM open for that requested profile. > > And last, power optimizations with DSPs typically come from additional > latency helping put the SoC in low-power modes. That's not necessarily > ideal for all usages, e.g. for music recording and mixing I am not > convinced the DSP path would help at all. > That's true. At the same time, this feature is more for power related benefits, not specifically for performance. (although we haven't seen any performance related issues w/ this approach on the audio profiles the DSP supports) I think if its an audio profile that supports a high sample rate and large number of channels, then the DSP wouldn't be able to support it anyway, and userspace could still use the legacy path. This would allow for those high-performance audio devices to not be affected. Thanks Wesley Cheng
>> On 12/23/22 17:31, 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. >> >> It would be nice to clarify what you want to offload >> a) audio data transfers for isoc ports >> b) control for e.g. volume settings (those go to endpoint 0 IIRC) >> c) Both? >> > > Thanks for sharing your experience, and inputs! > > It would be the audio related endpoints only, so ISOC and potentially > feedback ep. That's good, that means there's a common basis for at least two separate hardware implementations. >> This has a lot of implications on the design. ASoC/DPCM is mainly >> intended for audio data transfers, control is a separate problem with >> configurations handled with register settings or bus-specific commands. >> > > Control would still be handled by the main processor. Excellent, one more thing in common. Maintainers like this sort of alignment :-) >>> 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. To the best of my knowledge this isn't needed on Intel platforms, but that's something we would need to double-check. >>> 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... >> >> You would still need some sort of mutual exclusion to make sure the isoc >> endpoints are not used concurrently by the two cards. Relying on >> userspace intelligence to enforce that exclusion is not safe IMHO. >> > > Sure, I think we can make the USB card as being used if the offloading > path is currently being enabled. Kernel could return an error to > userspace when this situation happens. It's problematic for servers such as PipeWire/PulseAudio that open all possible PCMs to figure out what they support in terms of formats. I am not sure we can enforce a user-space serialization when discovering capabilities? > >> Intel looked at this sort of offload support a while ago and our >> directions were very different - for a variety of reasons USB offload is >> enabled on Windows platforms but remains a TODO for Linux. Rather than >> having two cards, you could have a single card and addition subdevices >> that expose the paths through the DSP. The benefits were that there was >> a single set of controls that userspace needed to know about, and volume >> settings were the same no matter which path you used (legacy or >> DSP-optimized paths). That's consistent with the directions to use 'Deep >> Buffer' PCM paths for local playback, it's the same idea of reducing >> power consumption with optimized routing. >> > > Volume control would still be done through the legacy path as mentioned > above. For example, if a USB headset w/ a HID interface exposed (for > volume control) was connected, those HID events would be routed to > userspace to adjust volume accordingly on the main processor. (although > you're right about having separate controls still present - one for the > ASoC card and another for USB card) The two sets of controls implied by the use of two cards is really problematic IMHO. This adds complexity for userspace to figure out that the controls are really the same and synchronize/mirror changes. The premise of offload is that it should really not get in the way of user-experience, design constructs that result in delayed starts/stop, changed volumes or quality differences should be avoided, or users/distros will disable this optimization. One card with additional DSP-based PCM devices seems simpler to me in terms of usage, but it's not without technical challenges either: with the use of the ASoC topology framework we only know what the DSP supports when registering a card and probing the ASoC components. The interaction between USB audio and ASoC would also be at least as complicated as display audio, in that it needs to work no matter what the probe order is, and even survive the Linux device/driver model requirement that there are no timing dependencies in the driver bind/unbind sequences. >> Another point is that there may be cases where the DSP paths are not >> available if the DSP memory and MCPS budget is exceeded. In those cases, >> the DSP parts needs the ability to notify userspace that the legacy path >> should be used. > > If we ran into this scenario, the audio DSP AFE port start command would > fail, and this would be propagated to the userspace entity. It could > then potentially re-route to the legacy/non-offload path. 'start' or 'open'? This is a rather important design difference. Usually we try to make decisions in the .open or .hw_params stage. The 'start' or 'trigger' are usually not meant to fail due to unavailable resources in ALSA. >> Another case to handle is that some USB devices can handle way more data >> than DSPs can chew, for example Pro audio boxes that can deal with 8ch >> 192kHz will typically use the legacy paths. Some also handle specific >> formats such as DSD over PCM. So it's quite likely that PCM devices for >> card0 and card1 above do NOT expose support for the same formats, or put >> differently that only a subset of the USB device capabilities are >> handled through the DSP. > > Same as the above. We have programmed the USB backend to support the > profiles that the audio DSP can handle. I assume if there was any other > request, the userspace entity would fail the PCM open for that requested > profile. What's not clear to me is whether there's any matching process between the DSP capabilities and what the USB device exposes? if the USB device is already way more complicated that what the ASoC back-end can deal with, why expose a card? >> And last, power optimizations with DSPs typically come from additional >> latency helping put the SoC in low-power modes. That's not necessarily >> ideal for all usages, e.g. for music recording and mixing I am not >> convinced the DSP path would help at all. >> > > That's true. At the same time, this feature is more for power related > benefits, not specifically for performance. (although we haven't seen > any performance related issues w/ this approach on the audio profiles > the DSP supports) I think if its an audio profile that supports a high > sample rate and large number of channels, then the DSP wouldn't be able > to support it anyway, and userspace could still use the legacy path. > This would allow for those high-performance audio devices to not be > affected. ok, we are aligned as well here. Excellent. With the on-going work to introduce 'Deep Buffer' capabilities, we'll have a need to tag PCM devices with a usage or 'modifier', or have this information in UCM/topology. Logic will have to be introduced in userspace to use the best routing, I would think this work can be reused for USB cases to indicate the offload solution is geared to power optimizations.
Hi Pierre, On 1/6/2023 7:57 AM, Pierre-Louis Bossart wrote: > >>> On 12/23/22 17:31, 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. >>> >>> It would be nice to clarify what you want to offload >>> a) audio data transfers for isoc ports >>> b) control for e.g. volume settings (those go to endpoint 0 IIRC) >>> c) Both? >>> >> >> Thanks for sharing your experience, and inputs! >> >> It would be the audio related endpoints only, so ISOC and potentially >> feedback ep. > > That's good, that means there's a common basis for at least two separate > hardware implementations. >>> This has a lot of implications on the design. ASoC/DPCM is mainly >>> intended for audio data transfers, control is a separate problem with >>> configurations handled with register settings or bus-specific commands. >>> >> >> Control would still be handled by the main processor. > > Excellent, one more thing in common. Maintainers like this sort of > alignment :-) > >>>> 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. > > To the best of my knowledge this isn't needed on Intel platforms, but > that's something we would need to double-check. I think Mathias mentioned that he was looking into adding some XHCI secondary interrupter support as well. However, it did have some slightly different requirements compared to what this offloading feature is trying to do. I'll first have to split up the XHCI/HCD changes into separate parts (interrupter specific and offloading specific), and then I'll work with him to see what can be improved from there. >>>> 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... >>> >>> You would still need some sort of mutual exclusion to make sure the isoc >>> endpoints are not used concurrently by the two cards. Relying on >>> userspace intelligence to enforce that exclusion is not safe IMHO. >>> >> >> Sure, I think we can make the USB card as being used if the offloading >> path is currently being enabled. Kernel could return an error to >> userspace when this situation happens. > > It's problematic for servers such as PipeWire/PulseAudio that open all > possible PCMs to figure out what they support in terms of formats. I am > not sure we can enforce a user-space serialization when discovering > capabilities? > I see...I'm not too familiar yet with all the different implementations from userspace yet, so that is something I'll need to look up on the side. Takashi, would you happen to have any inputs with regards to how flexible PCM device selection can be from the userspace level? If the offload PCM device can't be supported, can it fallback to another PCM device? >> >>> Intel looked at this sort of offload support a while ago and our >>> directions were very different - for a variety of reasons USB offload is >>> enabled on Windows platforms but remains a TODO for Linux. Rather than >>> having two cards, you could have a single card and addition subdevices >>> that expose the paths through the DSP. The benefits were that there was >>> a single set of controls that userspace needed to know about, and volume >>> settings were the same no matter which path you used (legacy or >>> DSP-optimized paths). That's consistent with the directions to use 'Deep >>> Buffer' PCM paths for local playback, it's the same idea of reducing >>> power consumption with optimized routing. >>> >> >> Volume control would still be done through the legacy path as mentioned >> above. For example, if a USB headset w/ a HID interface exposed (for >> volume control) was connected, those HID events would be routed to >> userspace to adjust volume accordingly on the main processor. (although >> you're right about having separate controls still present - one for the >> ASoC card and another for USB card) > > The two sets of controls implied by the use of two cards is really > problematic IMHO. This adds complexity for userspace to figure out that > the controls are really the same and synchronize/mirror changes. > > The premise of offload is that it should really not get in the way of > user-experience, design constructs that result in delayed starts/stop, > changed volumes or quality differences should be avoided, or > users/distros will disable this optimization. > Makes sense. I think in terms of controls, we know that for an USB audio device, anything will still be handled through the USB card. Again, since I'm not too familiar yet with all the userspace implementations, does it have mechanisms to treat the control and data interfaces separately? > One card with additional DSP-based PCM devices seems simpler to me in > terms of usage, but it's not without technical challenges either: with > the use of the ASoC topology framework we only know what the DSP > supports when registering a card and probing the ASoC components. > > The interaction between USB audio and ASoC would also be at least as > complicated as display audio, in that it needs to work no matter what > the probe order is, and even survive the Linux device/driver model > requirement that there are no timing dependencies in the driver > bind/unbind sequences. > Yes, this was my initial approach as well, but from the technical perspective it was very very messy, and potentially could have affected functionality on certain devices if not handled correctly. I think the difficult part was that the USB SND framework itself is an independent entity, and it was tough to dissect the portions which created PCM/sound card devices. I don't think that was something which would have gone well if introduced all at once. It would require a lot of discussion before getting the proper implementation. At least this series introduces the initial communication between ASoC and USB SND, and maybe as use cases become clearer we can always improve/build on top of it. >>> Another point is that there may be cases where the DSP paths are not >>> available if the DSP memory and MCPS budget is exceeded. In those cases, >>> the DSP parts needs the ability to notify userspace that the legacy path >>> should be used. >> >> If we ran into this scenario, the audio DSP AFE port start command would >> fail, and this would be propagated to the userspace entity. It could >> then potentially re-route to the legacy/non-offload path. > > 'start' or 'open'? This is a rather important design difference. Usually > we try to make decisions in the .open or .hw_params stage. The 'start' > or 'trigger' are usually not meant to fail due to unavailable resources > in ALSA. This happens during the .prepare() phase. >>> Another case to handle is that some USB devices can handle way more data >>> than DSPs can chew, for example Pro audio boxes that can deal with 8ch >>> 192kHz will typically use the legacy paths. Some also handle specific >>> formats such as DSD over PCM. So it's quite likely that PCM devices for >>> card0 and card1 above do NOT expose support for the same formats, or put >>> differently that only a subset of the USB device capabilities are >>> handled through the DSP. >> >> Same as the above. We have programmed the USB backend to support the >> profiles that the audio DSP can handle. I assume if there was any other >> request, the userspace entity would fail the PCM open for that requested >> profile. > > What's not clear to me is whether there's any matching process between > the DSP capabilities and what the USB device exposes? if the USB device > is already way more complicated that what the ASoC back-end can deal > with, why expose a card? > That's something I thought was done by the ASoC core. I can check that and see if that's the case. There is a check added in hw_params of our ASoC component where we do query the USB audio descriptors to ensure that the PCM format being used is supported by the device. I guess this is when the DSP capabilities are better than what the headset can support :). >>> And last, power optimizations with DSPs typically come from additional >>> latency helping put the SoC in low-power modes. That's not necessarily >>> ideal for all usages, e.g. for music recording and mixing I am not >>> convinced the DSP path would help at all. >>> >> >> That's true. At the same time, this feature is more for power related >> benefits, not specifically for performance. (although we haven't seen >> any performance related issues w/ this approach on the audio profiles >> the DSP supports) I think if its an audio profile that supports a high >> sample rate and large number of channels, then the DSP wouldn't be able >> to support it anyway, and userspace could still use the legacy path. >> This would allow for those high-performance audio devices to not be >> affected. > > ok, we are aligned as well here. Excellent. With the on-going work to > introduce 'Deep Buffer' capabilities, we'll have a need to tag PCM > devices with a usage or 'modifier', or have this information in > UCM/topology. Logic will have to be introduced in userspace to use the > best routing, I would think this work can be reused for USB cases to > indicate the offload solution is geared to power optimizations. Great, I like that idea to see if we can help userspace choose the desired path based on what the overall system is looking for. I wonder if that would also potentially help with some of the PCM device selection complexities you brought up as well. If the system just wants best possible performance then it would just completely ignore the power optimized (offload) path for any device. Thanks Wesley Cheng
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 Wesley Cheng (14): ASoC: Add SOC USB APIs for adding an USB backend ASoC: qcom: qdsp6: Introduce USB AFE port to q6dsp ASoC: qcom: Add USB backend ASoC driver for Q6 sound: usb: card: Introduce USB SND vendor op callbacks sound: usb: Export USB SND APIs for modules usb: core: hcd: Introduce USB HCD APIs for interrupter management usb: host: xhci: Add XHCI secondary interrupter support usb: dwc3: Add DT parameter to specify maximum number of interrupters sound: usb: Introduce QC USB SND offloading support sound: usb: card: Check for support for requested audio format sound: soc: soc-usb: Add PCM format check API for USB backend sound: soc: qcom: qusb6: Ensure PCM format is supported by USB audio device ASoC: dt-bindings: Add Q6USB backend bindings ASoC: dt-bindings: Update example for enabling USB offload on SM8250 .../bindings/sound/qcom,q6usb-dais.yaml | 55 + .../bindings/sound/qcom,sm8250.yaml | 13 + drivers/usb/core/hcd.c | 86 + drivers/usb/dwc3/core.c | 12 + drivers/usb/dwc3/core.h | 2 + drivers/usb/dwc3/host.c | 5 +- drivers/usb/host/xhci-mem.c | 219 ++- drivers/usb/host/xhci-plat.c | 2 + drivers/usb/host/xhci.c | 169 +- drivers/usb/host/xhci.h | 15 + .../sound/qcom,q6dsp-lpass-ports.h | 1 + include/linux/usb.h | 7 + include/linux/usb/hcd.h | 16 +- include/sound/q6usboffload.h | 20 + include/sound/soc-usb.h | 34 + sound/soc/Makefile | 2 +- sound/soc/qcom/Kconfig | 4 + sound/soc/qcom/qdsp6/Makefile | 1 + sound/soc/qcom/qdsp6/q6afe-dai.c | 47 + sound/soc/qcom/qdsp6/q6afe.c | 183 ++ sound/soc/qcom/qdsp6/q6afe.h | 46 +- sound/soc/qcom/qdsp6/q6dsp-lpass-ports.c | 23 + sound/soc/qcom/qdsp6/q6dsp-lpass-ports.h | 1 + sound/soc/qcom/qdsp6/q6routing.c | 8 + sound/soc/qcom/qdsp6/q6usb.c | 239 +++ sound/soc/soc-usb.c | 79 + sound/usb/Kconfig | 14 + sound/usb/Makefile | 2 +- sound/usb/card.c | 43 + sound/usb/card.h | 10 + sound/usb/endpoint.c | 2 + sound/usb/helper.c | 1 + sound/usb/pcm.c | 9 +- sound/usb/pcm.h | 12 + sound/usb/qcom/Makefile | 2 + sound/usb/qcom/qc_audio_offload.c | 1610 +++++++++++++++++ sound/usb/qcom/usb_audio_qmi_v01.c | 892 +++++++++ sound/usb/qcom/usb_audio_qmi_v01.h | 162 ++ 38 files changed, 3998 insertions(+), 50 deletions(-) create mode 100644 Documentation/devicetree/bindings/sound/qcom,q6usb-dais.yaml 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