On 9/25/2024 2:59 AM, Wesley Cheng wrote:
With the introduction of the soc-usb driver, add documentation highlighting details on how to utilize the new driver and how it interacts with different components in USB SND and ASoC. It provides examples on how to implement the drivers that will need to be introduced in order to enable USB audio offloading. Signed-off-by: Wesley Cheng <quic_wcheng@xxxxxxxxxxx> ---
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+USB Offload Related Kcontrols +============================= +Details +------- +A set of kcontrols can be utilized by applications to help select the proper sound +devices to enable USB audio offloading. SOC USB exposes the get_offload_dev() +callback that designs can use to ensure that the proper indices are returned to the +application. + +Implementation +-------------- + +**Example:** + + **Sound Cards**: + + :: + + 0 [SM8250MTPWCD938]: sm8250 - SM8250-MTP-WCD9380-WSA8810-VA-D + SM8250-MTP-WCD9380-WSA8810-VA-DMIC + 1 [Seri ]: USB-Audio - Plantronics Blackwire 3225 Seri + Plantronics Plantronics Blackwire + 3225 Seri at usb-xhci-hcd.1.auto-1.1, + full sp + 2 [C320M ]: USB-Audio - Plantronics C320-M + Plantronics Plantronics C320-M at usb-xhci-hcd.1.auto-1.2, full speed + + **USB Sound Card** - card#1: + + :: + + USB Offload Playback Route PCM#0 -1, -1 (range -1->255) + + **USB Sound Card** - card#2: + + :: + + USB Offload Playback Route PCM#0 0, 1 (range -1->255) + +The above example shows a scenario where the system has one ASoC platform card +(card#0) and two USB sound devices connected (card#1 and card#2). When reading +the available kcontrols for each USB audio device, the following kcontrol lists +the mapped offload path for the specific device: + + ``USB Offload Playback Route#*`` +
Those examples would probably be easier to follow if you also provided something similar to "aplay -l" output in addition to above sound card list.
+The kcontrol is indexed, because a USB audio device could potentially have +several PCM devices. The above kcontrols are defined as: + + - ``USB Offload Playback Route PCM`` **(R)**: Returns the ASoC platform sound + card and PCM device index. The output **"0, 1"** (card index, PCM device index) + signifies that there is an available offload path for the USB SND device + through card#0 - PCM device#1. If **"-1, -1"** is seen, then no offload path is + available for the USB SND device. +
