linux-kernel - Re: [RFC PATCH 03/14] ASoC: qcom: Add USB backend ASoC driver for Q6

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Date:   Tue, 27 Dec 2022 15:02:31 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     Mark Brown <broonie@...nel.org>,
        Wesley Cheng <quic_wcheng@...cinc.com>,
        srinivas.kandagatla@...aro.org, mathias.nyman@...el.com,
        perex@...ex.cz, lgirdwood@...il.com, andersson@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, Thinh.Nguyen@...opsys.com,
        bgoswami@...cinc.com, tiwai@...e.com, robh+dt@...nel.org,
        agross@...nel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-usb@...r.kernel.org,
        quic_jackp@...cinc.com, quic_plai@...cinc.com
Subject: Re: [RFC PATCH 03/14] ASoC: qcom: Add USB backend ASoC driver for Q6

On Tue, 27 Dec 2022 14:45:13 +0100,
Greg KH wrote:
> 
> On Tue, Dec 27, 2022 at 01:04:55PM +0000, Mark Brown wrote:
> > On Sat, Dec 24, 2022 at 10:02:59AM +0100, Greg KH wrote:
> > > On Fri, Dec 23, 2022 at 03:31:49PM -0800, Wesley Cheng wrote:
> > 
> > > > + * struct q6usb_offload
> > > > + * @dev - dev handle to usb be
> > 
> > > "be"?  What is that?
> > 
> > Back end.  This is a concept in DPCM which should be reasonably
> > discoverable to people working on the audio portions of this code.
> 
> Ok, then how is the reference counting logic handled here?  USB devices
> can be removed from the system at any point in time...

The whole picture is fairly complex, and this patch is a part
belonging to the ASoC machine driver -- that is, it's bound to the
Qualcomm host, and there can be only one on a system.  

OTOH, USB audio devices are still managed by the existing USB audio
driver as is, and they can be multiple and any devices.  The basic
idea here is a hijack of the USB data processing in USB audio driver
with the offloading mechanism by this ASoC driver (only if the
condition met).


thanks,

Takashi