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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. As part of step#2, the audio DSP is aware of the USB SND card and pcm device index that is being selected, and is communicated as part of the QMI request received by QC audio offload. These indices will be used to handle the stream enable QMI request. Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com> Acked-by: Mark Brown <broonie@kernel.org> Link: https://lore.kernel.org/r/20250409194804.3773260-29-quic_wcheng@quicinc.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.