linux-kernel - Re: [PATCH v33 30/31] ALSA: usb-audio: qcom: Add USB offload route kcontrol

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Message-ID: <9c266af7-b377-4f3e-8a6d-f7d4fa44d465@infradead.org>
Date: Thu, 16 Jan 2025 16:08:27 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Wesley Cheng <quic_wcheng@...cinc.com>, 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, tiwai@...e.com, krzk+dt@...nel.org,
 pierre-louis.bossart@...ux.dev, Thinh.Nguyen@...opsys.com, robh@...nel.org,
 gregkh@...uxfoundation.org
Cc: 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
Subject: Re: [PATCH v33 30/31] ALSA: usb-audio: qcom: Add USB offload route
 kcontrol



On 1/16/25 3:28 PM, Wesley Cheng wrote:
> In order to allow userspace/applications know about USB offloading status,
> expose a sound kcontrol that fetches information about which sound card
> and PCM index the USB device is mapped to for supporting offloading.  In
> the USB audio offloading framework, the ASoC BE DAI link is the entity
> responsible for registering to the SOC USB layer.
> 
> It is expected for the USB SND offloading driver to add the kcontrol to the
> sound card associated with the USB audio device.  An example output would
> look like:
> 
> tinymix -D 1 get 'USB Offload Playback Route PCM#0'
> -1, -1 (range -1->255)
> 
> This example signifies that there is no mapped ASoC path available for the
> USB SND device.
> 
> tinymix -D 1 get 'USB Offload Playback Route PCM#0'
> 0, 0 (range -1->255)
> 
> This example signifies that the offload path is available over ASoC sound
> card index#0 and PCM device#0.
> 
> The USB offload kcontrol will be added in addition to the existing
> kcontrols identified by the USB SND mixer.  The kcontrols used to modify
> the USB audio device specific parameters are still valid and expected to be
> used.  These parameters are not mirrored to the ASoC subsystem.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
> ---
>  sound/usb/Kconfig                  |  10 ++
>  sound/usb/qcom/Makefile            |   4 +
>  sound/usb/qcom/mixer_usb_offload.c | 158 +++++++++++++++++++++++++++++
>  sound/usb/qcom/mixer_usb_offload.h |  17 ++++
>  sound/usb/qcom/qc_audio_offload.c  |   2 +
>  5 files changed, 191 insertions(+)
>  create mode 100644 sound/usb/qcom/mixer_usb_offload.c
>  create mode 100644 sound/usb/qcom/mixer_usb_offload.h
> 

> diff --git a/sound/usb/qcom/mixer_usb_offload.c b/sound/usb/qcom/mixer_usb_offload.c
> new file mode 100644
> index 000000000000..2696eb145ef5
> --- /dev/null
> +++ b/sound/usb/qcom/mixer_usb_offload.c
> @@ -0,0 +1,158 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2022-2025 Qualcomm Innovation Center, Inc. All rights reserved.
> + */
> +
> +#include <linux/usb.h>
> +

[snip]

> +
> +/**
> + * snd_usb_offload_create_ctl() - Add USB offload bounded mixer
> + * @chip - USB SND chip device

Use ':' instead of '-'.

> + *
> + * Creates a sound control for a USB audio device, so that applications can
> + * query for if there is an available USB audio offload path, and which
> + * card is managing it.
> + */
> +int snd_usb_offload_create_ctl(struct snd_usb_audio *chip)
> +{

-- 
~Randy