Message-ID: <7d5fd3bf-c33e-4274-938b-2fb93c4b39d8@quicinc.com>
Date: Wed, 2 Apr 2025 17:23:34 -0700
From: Wesley Cheng <quic_wcheng@...cinc.com>
To: Stephan Gerhold <stephan.gerhold@...aro.org>
CC: <srinivas.kandagatla@...aro.org>, <mathias.nyman@...el.com>,
        <perex@...ex.cz>, <conor+dt@...nel.org>, <dmitry.torokhov@...il.com>,
        <corbet@....net>, <broonie@...nel.org>, <lgirdwood@...il.com>,
        <krzk+dt@...nel.org>, <pierre-louis.bossart@...ux.intel.com>,
        <Thinh.Nguyen@...opsys.com>, <tiwai@...e.com>, <robh@...nel.org>,
        <gregkh@...uxfoundation.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-sound@...r.kernel.org>,
        <linux-input@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        Luca Weiss
	<luca.weiss@...rphone.com>
Subject: Re: [PATCH v36 22/31] ASoC: qcom: qdsp6: Introduce USB AFE port to
 q6dsp

Hi Stephan,

On 4/2/2025 7:41 AM, Stephan Gerhold wrote:
> On Tue, Apr 01, 2025 at 04:47:41PM -0700, Wesley Cheng wrote:
>> On 4/1/2025 1:16 AM, Stephan Gerhold wrote:
>>> On Mon, Mar 31, 2025 at 12:52:19PM -0700, Wesley Cheng wrote:
>>>> On 3/26/2025 2:57 AM, Stephan Gerhold wrote:
>>>>> On Tue, Mar 25, 2025 at 04:18:03PM -0700, Wesley Cheng wrote:
>>>>>> On 3/25/2025 2:24 AM, Stephan Gerhold wrote:
>>>>>>> On Tue, Mar 18, 2025 at 05:51:32PM -0700, Wesley Cheng wrote:
>>>>>>>> The QC ADSP is able to support USB playback endpoints, so that the main
>>>>>>>> application processor can be placed into lower CPU power modes.  This adds
>>>>>>>> the required AFE port configurations and port start command to start an
>>>>>>>> audio session.
>>>>>>>>
>>>>>>>> Specifically, the QC ADSP can support all potential endpoints that are
>>>>>>>> exposed by the audio data interface.  This includes isochronous data
>>>>>>>> endpoints, in either synchronous mode or asynchronous mode. In the latter
>>>>>>>> case both implicit or explicit feedback endpoints are supported.  The size
>>>>>>>> of audio samples sent per USB frame (microframe) will be adjusted based on
>>>>>>>> information received on the feedback endpoint.
>>>>>>>>
>>>>>>>> Some pre-requisites are needed before issuing the AFE port start command,
>>>>>>>> such as setting the USB AFE dev_token.  This carries information about the
>>>>>>>> available USB SND cards and PCM devices that have been discovered on the
>>>>>>>> USB bus.  The dev_token field is used by the audio DSP to notify the USB
>>>>>>>> offload driver of which card and PCM index to enable playback on.
>>>>>>>>
>>>>>>>> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
>>>>>>>> ---
>>>>>>>>   sound/soc/qcom/qdsp6/q6afe-dai.c         |  60 +++++++
>>>>>>>>   sound/soc/qcom/qdsp6/q6afe.c             | 192 ++++++++++++++++++++++-
>>>>>>>>   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         |  32 +++-
>>>>>>>>   6 files changed, 341 insertions(+), 3 deletions(-)
>>>>>>>>
>>>>>> [...]
>>>>>>>> diff --git a/sound/soc/qcom/qdsp6/q6routing.c b/sound/soc/qcom/qdsp6/q6routing.c
>>>>>>>> index 90228699ba7d..b7439420b425 100644
>>>>>>>> --- a/sound/soc/qcom/qdsp6/q6routing.c
>>>>>>>> +++ b/sound/soc/qcom/qdsp6/q6routing.c
>>>>>>>> @@ -435,6 +435,26 @@ static struct session_data *get_session_from_id(struct msm_routing_data *data,
>>>>>>>>   	return NULL;
>>>>>>>>   }
>>>>>>>> +
>>>>>>>> +static bool is_usb_routing_enabled(struct msm_routing_data *data)
>>>>>>>> +{
>>>>>>>> +	int i;
>>>>>>>> +
>>>>>>>> +	/*
>>>>>>>> +	 * Loop through current sessions to see if there are active routes
>>>>>>>> +	 * to the USB_RX backend DAI.  The USB offload routing is designed
>>>>>>>> +	 * similarly to the non offload path.  If there are multiple PCM
>>>>>>>> +	 * devices associated with the ASoC platform card, only one active
>>>>>>>> +	 * path can be routed to the USB offloaded endpoint.
>>>>>>>> +	 */
>>>>>>>> +	for (i = 0; i < MAX_SESSIONS; i++) {
>>>>>>>> +		if (data->sessions[i].port_id == USB_RX)
>>>>>>>> +			return true;
>>>>>>>> +	}
>>>>>>>> +
>>>>>>>> +	return false;
>>>>>>>> +}
>>>>>>>
>>>>>>> What is different about USB_RX compared to other output ports we have in
>>>>>>> Q6AFE? Obviously, we can only play one stream on an output port. But
>>>>>>> doesn't the ADSP mix streams together when you have multiple routes?
>>>>>>>
>>>>>>
>>>>>> This patch will limit the USB_RX from being able to be mixed to multiple
>>>>>> q6adm paths.
>>>>>>
>>>>>>> Also, this doesn't actually check for *active* routes only. It just
>>>>>>> looks if any other MultiMedia DAI is configured to output to USB_RX.
>>>>>>> That doesn't mean they will ever be active at the same time.
>>>>>>>
>>>>>>
>>>>>> Yes, the main reason being that that is the mechanism we use to populate
>>>>>> the active offload path within the USB SND card mixer.
>>>>>>
>>>>>>> I might for example want to have MultiMedia1 and MultiMedia2 both
>>>>>>> configured to output to USB_RX. Let's assume MultiMedia1 is a normal PCM
>>>>>>> DAI, MultiMedia2 is a compress offload DAI. When I want to playback
>>>>>>> normal audio, I go through MultiMedia1, when I want to play compressed
>>>>>>> audio, I go through MultiMedia2. Only one of them active at a time.
>>>>>>> Why can't I set this up statically in the mixers?
>>>>>>>
>>>>>>> If you confirm that it is really impossible to have multiple streams
>>>>>>> mixed together to the USB_RX output in the ADSP, then this should be a
>>>>>>> runtime check instead when starting the stream IMO.
>>>>>>>
>>>>>>
>>>>>> We can have multiple streams being mixed together, but it will get
>>>>>> confusing because it changes the definition that we had discussed about in
>>>>>> the past about the overall design for the interaction w/ userspace.
>>>>>> Although we (QC) only support a single USB audio device for offloading,
>>>>>> there could be other situations where the audio DSP can support multiple
>>>>>> devices.  The assumption is that each MM path is assigned to a USB device.
>>>>>>
>>>>>
>>>>> Are you referring to the "USB Offload Playback Route PCM#*" mixers here?
>>>>> They could just refer to first of the configured MM paths, if someone
>>>>> decides to route multiple paths to the USB backend. Looking at
>>>>> q6usb_update_offload_route(), I think the implementation does that
>>>>> already.
>>>>>
>>>>> I think it's fine that the userspace API for automatically "probing" the
>>>>> PCM device supports only a single path to the USB backend. But if
>>>>> someone wants to bypass the automatic probing and configure a more
>>>>> advanced setup, do we need to forbid that?
>>>>>
>>>>> Asked differently: what would happen if we remove this check here and
>>>>> handle USB_RX like any other Q6AFE output port? Would anything break for
>>>>> the userspace interface?
>>>>>
>>>>
>>>> So I took a look at seeing how the Q6ADM/ASM interactions would work for
>>>> the situation where if user tried to start both MM1/2 streams at the same
>>>> time over the USB offload path.  In this scenario, we see that the Q6USB BE
>>>> DAI operations, ie startup, hw_params, etc... gets called one time for the
>>>> initial stream.  For example, if I start playback on MM1, then that
>>>> triggers the USB BE DAI to be brought up.
>>>>
>>>> When I start playback on MM2, since MM1 already called
>>>> dpcm_be_dai_startup(), then be->dpcm[stream].users will be greater than
>>>> zero.  This would cause the __soc_pcm_open() to be skipped for the USB BE
>>>> DAI, so I wouldn't be able to check the runtime status at the Q6USB backend
>>>> DAI.  However, we do track current streaming sessions done over Q6 ADM and
>>>> it does save the AFE port associated to each COPP allocation, so I think its
>>>> reasonable to see if there is already a COPP entry for the USB AFE port, to
>>>> fail the open() call associated to the FE DAI.
>>>>
>>>
>>> This sounds like a reasonable approach *if* we have to prevent multiple
>>> MM DAIs from streaming to the USB AFE port at the same time.
>>>
>>> It's still unclear to me why we have to introduce this limitation in the
>>> first place. I think the questions from my previous email are still
>>> open. Can you check them again?
>>>
>>
>> So I checked with our audio DSP folks, and they mentioned there isn't
>> technically a limitation from mixing multiple ADM streams from their end.
>> My observations are as follows:
>> - Using tinyplay to open and play on different FE PCM devices (ie MM1 and
>> MM2), both streams are audible on the USB headset (intermixed).
>> - If starting playback on MM1 first, before MM2, then once playback is
>> complete on MM1, the ADM close is also affecting the MM2 stream.
>> Basically, MM2 stops when the MM1 audio file is completed.
>> - Due to the abrupt/incomplete closing of the MM2 ADM stream, looks like
>> the audio DSP is not handling that case well, so subsequent playbacks fail.
>>
> 
> Thanks a lot for testing this!
> 
>> I did find a possible reason for this, and it seems to be due to some code
>> unrelated to the USB offload path directly.  It looks like the Q6ADM is
>> currently built in a way that you can only route streams to a single
>> endpoint, even though we do have reference counting for each COPP profile.
>> So even after the first MM1 ADM stream completes and the PCM device is
>> closed, the MM1 ADM close callback will issue a q6adm_device_close() for
>> the USB AFE port.
> 
> Yeah, this sounds like a bug to me...
> 
>>
>> I made some test changes to account for the refcount before issuing the
>> q6adm_device_close(), and that seemed to work.  Once the MM1 stream closes,
>> it allows for the MM2 stream to close/finish before issuing the command,
>> and that allows for proper cleanup of the audio data.
>>
>> IMO, I would like to keep the initial behavior (ie, blocking the additional
>> stream open from the kernel) until I can get some more testing done, and
>> figure out if this is the correct approach.  If it is, I can submit a
>> follow up series to address it.
>>
> 
> I'm fine with this approach. My only two concerns/comments are:
> 
>   1. Let's make sure we don't waste too much time finding the ideal
>      approach to implement the additional blocking, if this will likely
>      end up getting removed again anyway.
> 
>   2. How can we justify making this change only for USB? Your analysis
>      sounds like the issue applies to all types of output ports. This was
>      exactly my main concern with the check you added in this patch:
>      I would expect QDSP6 treats all ports exactly the same. This means
>      we should add this additional check for all the output ports...
> 

Fair points...I will extend this check across all ports until I get back 
with seeing how we can address the mixing situation.

Thanks
Wesley Cheng

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