linux-kernel - Re: [RFC PATCH 09/14] sound: usb: Introduce QC USB SND offloading support

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Message-ID: <cc40d2e2-3384-cd64-f53c-a0811b53d781@quicinc.com>
Date:   Thu, 5 Jan 2023 17:06:00 -0800
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        <srinivas.kandagatla@...aro.org>, <mathias.nyman@...el.com>,
        <perex@...ex.cz>, <broonie@...nel.org>, <lgirdwood@...il.com>,
        <andersson@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
        <gregkh@...uxfoundation.org>, <Thinh.Nguyen@...opsys.com>,
        <bgoswami@...cinc.com>, <tiwai@...e.com>, <robh+dt@...nel.org>,
        <agross@...nel.org>
CC:     <devicetree@...r.kernel.org>, <alsa-devel@...a-project.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <quic_jackp@...cinc.com>,
        <quic_plai@...cinc.com>
Subject: Re: [RFC PATCH 09/14] sound: usb: Introduce QC USB SND offloading
 support

Hi Pierre,

On 1/4/2023 3:51 PM, Pierre-Louis Bossart wrote:
> 
> 
> On 12/23/22 17:31, Wesley Cheng wrote:
>> Several Qualcomm SoCs have a dedicated audio DSP, which has the ability to
>> support USB sound devices.  This vendor driver will implement the required
>> handshaking with the DSP, in order to pass along required resources that
>> will be utilized by the DSP's USB SW.  The communication channel used for
>> this handshaking will be using the QMI protocol.  Required resources
>> include:
>> - Allocated secondary event ring address
>> - EP transfer ring address
>> - Interrupter number
>>
>> The above information will allow for the audio DSP to execute USB transfers
>> over the USB bus.  It will also be able to support devices that have an
>> implicit feedback and sync endpoint as well.  Offloading these data
>> transfers will allow the main/applications processor to enter lower CPU
>> power modes, and sustain a longer duration in those modes.
> 
> Are you suggesting that the entire feedback loop be handled in the DSP?
> It's not clear what "Offloading these data transfers" refers to, the
> data part or the feedback path?
> 

Yes, as mentioned in the cover letter response, we'll handle the 
feedback endpoints. (feedback eps are part of the audio data interface)

> Comments are almost inexistent in this patch so it's hard to figure out
> what it really does.
> 

OK, will add some more comments.

Thanks
Wesley Cheng