Re: [PATCH v5 18/32] sound: usb: Introduce QC USB SND offloading support

[Takashi Iwai]

On Tue, 29 Aug 2023 23:06:43 +0200,
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.
> 
> Audio offloading is initiated with the following sequence:
> 1. Userspace configures to route audio playback to USB backend and starts
> playback on the platform soundcard.
> 2. The Q6DSP AFE will communicate to the audio DSP to start the USB AFE
> port.
> 3. This results in a QMI packet with a STREAM enable command.
> 4. The QC audio offload driver will fetch the required resources, and pass
> this information as part of the QMI response to the STREAM enable command.
> 5. Once the QMI response is received the audio DSP will start queuing data
> on the USB bus.
> 
> Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx>
> ---
>  sound/usb/Kconfig                 |   15 +
>  sound/usb/Makefile                |    2 +-
>  sound/usb/qcom/Makefile           |    2 +
>  sound/usb/qcom/qc_audio_offload.c | 1813 +++++++++++++++++++++++++++++
>  4 files changed, 1831 insertions(+), 1 deletion(-)
>  create mode 100644 sound/usb/qcom/Makefile
>  create mode 100644 sound/usb/qcom/qc_audio_offload.c
> 
> diff --git a/sound/usb/Kconfig b/sound/usb/Kconfig
> index 4a9569a3a39a..da5838656baa 100644
> --- a/sound/usb/Kconfig
> +++ b/sound/usb/Kconfig
> @@ -176,6 +176,21 @@ config SND_BCD2000
>  	  To compile this driver as a module, choose M here: the module
>  	  will be called snd-bcd2000.
>  
> +config QC_USB_AUDIO_OFFLOAD

Keep SND_ prefix for consistency.  And, at best, align with the module
name.

> +	tristate "Qualcomm Audio Offload driver"
> +	depends on QCOM_QMI_HELPERS && SND_USB_AUDIO && USB_XHCI_SIDEBAND
> +	select SND_PCM
> +	help
> +	  Say Y here to enable the Qualcomm USB audio offloading feature.
> +
> +	  This module sets up the required QMI stream enable/disable
> +	  responses to requests generated by the audio DSP.  It passes the
> +	  USB transfer resource references, so that the audio DSP can issue
> +	  USB transfers to the host controller.
> +
> +	  To compile this driver as a module, choose M here: the module
> +	  will be called qc-audio-offload.

Hmm, you renamed it differently, no?  In the below:

> --- /dev/null
> +++ b/sound/usb/qcom/Makefile
> @@ -0,0 +1,2 @@
> +snd-usb-audio-qmi-objs := usb_audio_qmi_v01.o qc_audio_offload.o
> +obj-$(CONFIG_QC_USB_AUDIO_OFFLOAD) += snd-usb-audio-qmi.o

... it's called snd-usb-audio-qmi.


thanks,

Takashi