This is extendend version of "UAC2 Feedback endpoint" patch set I've sent back in 2020 [1]. It is extended with bi-directional Volume/Mute controls support for both UAC1 and UAC2 gadgets. It fixes issues with enumeration in various operation systems because of Feedback endpoint implementation, yet also adds new Volume/Mute support which allows developers to control UAC1/2 Gadget's Volume/Mute from the Host and in the same way UAC1/2 Gadget can control Volume/Mute of the Host making it closer to a real USB Audio card. This patch set should be applied on top of USB Audio Gadget part 1 fixes/improvements that I've sent previously to the mailing list [2] ============ UAC2 Feedback Endpoint support ============ Current UAC2 gadget implements capture/sync paths as two USB ISO ASYNC endpoints (IN and OUT). This violates USB spec which says that ISO ASYNC OUT endpoint should have feedback companion endpoint. See USB2.0 spec "5.12.4.1 Synchronization Type": asynchronous sink provides explicit feedback (isochronous pipe). Interesting that for ISO ASYNC *IN* endpoint respective feedback isn't required since source provides implicit feedforward (data stream). While it's not an issue if UAC2 Gadget is connected to Linux host (Linux ignores missing feedback endpoint), with other hosts like Windows or MacOS the UAC2 Gadget isn't enumerated due to missing feedback endpoint. This patch series adds feedback endpoint support to UAC2 function, new control to UAC2 mixer which can be used by userspace tools (like alsaloop from alsa-utils) for updating feedback frequency reported to the host. This is useful for usecases when UAC2 Gadget's audio samples are played to another codec or audio card with its own internal freerunning clock so host can be notified that more/less samples are required. The alsaloop tool requires some (relatively small) modifications in order to start support driving feedback frequency through UAC2 mixer control. That change have been sent as a separate patch to ALSA community [3]. Also added ability to switch ISO ASYNC OUT endpoint into adaptive endpoint which doesn't require feedback endpoint (as per USB spec). ======== UAC1/2 Volume/Mute controls support ========== Volume and Mute controls are traditionally presented in USB Audio cards that are available on the market, and Hosts usually expect they exist in the attached devices. However, Linux UAC gadget previosly didn't have such functinality which (depending on Host's operation system) was causing different behaviour: Linux hosts (usually) in this case can adjust volume by changing audio sample's amplitude that are sent to the gadget. Other hosts may stuck with maximum volume and can't adjust it for the Linux UAC gadget device. Volume/Mute controls support is quite useful feature. If implemented according to UAC1/2 spec, it allows to control volume in both directions: from the Host to Gadget and from Gadget to the Host. To do it, it's required to add new Feature Unit descriptor to existing UAC1/2 Gadget topology and add new interrupt endpoint so Volume/Mute changes can be reported to the Host. This has been tested with Linux/MacOS/Windows(7,10) hosts, by attaching alsamixer to the UAC1/2 ALSA card on Gadget side, and using available Volume/Mute control applications on the Hosts. An user can adjust Volume/Mute on the Host and see respective changes on the Gadget side. In the same way, an user can adjust Volume/Mute on the Gadget side and observe respective changes on the Host There is a known issue with Win7 which for some reason doesn't poll UAC1 interrupt endpoint causing Volume/Mute control not working in Gadget->Host direction ======================================================== Both features have been tested on BeagleBone Black and Raspberry PI 4 boards with Linux/MacOS/Windows(7,10) hosts. While on BeagleBone Black it works fine, Raspberry PI 4 DWC2 controller is affected by the DMA issue for control trasfers which I reported a while back in [4]. It is causing incorrect data provided by DWC2 UDC to UAC1/2 gadgets screwing up volume and mute control messages in the Host->Gadget direction. The hack is available (see [4]) but it leads to traces/issues with audio streaming. Patches reviews and testing on your HW is welcome as usual! [1] https://lore.kernel.org/linux-usb/1604794711-8661-1-git-send-email-ruslan.bilovol@xxxxxxxxx/ [2] https://lore.kernel.org/linux-usb/1614599375-8803-1-git-send-email-ruslan.bilovol@xxxxxxxxx/ [3] https://lore.kernel.org/linux-usb/1605220482-28487-1-git-send-email-ruslan.bilovol@xxxxxxxxx/ [4] https://lore.kernel.org/linux-usb/CAB=otbTVxa=nGWF4K1AYcYyPceYYRkC_1HYSb_Nhu6C9RMZEHA@xxxxxxxxxxxxxx/ Ruslan Bilovol (8): usb: gadget: u_audio: convert to strscpy usb: gadget: f_uac2/u_audio: add feedback endpoint support usb: gadget: f_uac2: add adaptive sync support for capture usb: gadget: u_audio: add real feedback implementation usb: audio-v2: add ability to define feature unit descriptor usb: gadget: u_audio: add bi-directional volume and mute support usb: gadget: f_uac2: add volume and mute support usb: gadget: f_uac1: add volume and mute support Documentation/ABI/testing/configfs-usb-gadget-uac1 | 10 + Documentation/ABI/testing/configfs-usb-gadget-uac2 | 11 + Documentation/usb/gadget-testing.rst | 37 +- drivers/usb/gadget/function/f_uac1.c | 674 +++++++++++++++++- drivers/usb/gadget/function/f_uac2.c | 764 +++++++++++++++++++-- drivers/usb/gadget/function/u_audio.c | 582 +++++++++++++++- drivers/usb/gadget/function/u_audio.h | 32 + drivers/usb/gadget/function/u_uac1.h | 20 + drivers/usb/gadget/function/u_uac2.h | 23 + include/linux/usb/audio-v2.h | 14 + 10 files changed, 2069 insertions(+), 98 deletions(-) -- 1.9.1
