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This patch adds a new function 'f_uac1' (f_uac1 with virtual "ALSA card") that uses recently created u_audio API. Comparing to legacy f_uac1 function implementation it doesn't require any real Audio codec to be present on the device. In f_uac1 audio streams are simply sinked to and sourced from a virtual ALSA sound card created using u_audio API. Legacy f_uac1 approach is to write audio samples directly to existing ALSA sound card f_uac1 approach is more generic/flexible one - create an ALSA sound card that represents USB Audio function and allows to be used by userspace application that may choose to do whatever it wants with the data received from the USB Host and choose to provide whatever it wants as audio data to the USB Host. f_uac1 also has capture support (gadget->host) thanks to easy implementation via u_audio. By default, capture interface has 48000kHz/2ch configuration, same as playback channel has. f_uac1 descriptors naming convention uses f_uac2 driver naming convention that makes it more common and meaningful. Comparing to f_uac1_legacy, the f_uac1 doesn't have volume/mute functionality. This is because the f_uac1 volume/mute feature unit was dummy implementation since that driver creation (2009) and never had any real volume control or mute functionality, so there is no any difference here. Since f_uac1 functionality, exposed interface to userspace (virtual ALSA card), input parameters are so different comparing to f_uac1_legacy, that there is no any reason to keep them in the same file/module, and separate function was created. g_audio can be built using one of existing UAC functions (f_uac1, f_uac1_legacy or f_uac2) Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com> Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com> |
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This directory attempts to document the ABI between the Linux kernel and userspace, and the relative stability of these interfaces. Due to the everchanging nature of Linux, and the differing maturity levels, these interfaces should be used by userspace programs in different ways. We have four different levels of ABI stability, as shown by the four different subdirectories in this location. Interfaces may change levels of stability according to the rules described below. The different levels of stability are: stable/ This directory documents the interfaces that the developer has defined to be stable. Userspace programs are free to use these interfaces with no restrictions, and backward compatibility for them will be guaranteed for at least 2 years. Most interfaces (like syscalls) are expected to never change and always be available. testing/ This directory documents interfaces that are felt to be stable, as the main development of this interface has been completed. The interface can be changed to add new features, but the current interface will not break by doing this, unless grave errors or security problems are found in them. Userspace programs can start to rely on these interfaces, but they must be aware of changes that can occur before these interfaces move to be marked stable. Programs that use these interfaces are strongly encouraged to add their name to the description of these interfaces, so that the kernel developers can easily notify them if any changes occur (see the description of the layout of the files below for details on how to do this.) obsolete/ This directory documents interfaces that are still remaining in the kernel, but are marked to be removed at some later point in time. The description of the interface will document the reason why it is obsolete and when it can be expected to be removed. removed/ This directory contains a list of the old interfaces that have been removed from the kernel. Every file in these directories will contain the following information: What: Short description of the interface Date: Date created KernelVersion: Kernel version this feature first showed up in. Contact: Primary contact for this interface (may be a mailing list) Description: Long description of the interface and how to use it. Users: All users of this interface who wish to be notified when it changes. This is very important for interfaces in the "testing" stage, so that kernel developers can work with userspace developers to ensure that things do not break in ways that are unacceptable. It is also important to get feedback for these interfaces to make sure they are working in a proper way and do not need to be changed further. How things move between levels: Interfaces in stable may move to obsolete, as long as the proper notification is given. Interfaces may be removed from obsolete and the kernel as long as the documented amount of time has gone by. Interfaces in the testing state can move to the stable state when the developers feel they are finished. They cannot be removed from the kernel tree without going through the obsolete state first. It's up to the developer to place their interfaces in the category they wish for it to start out in. Notable bits of non-ABI, which should not under any circumstances be considered stable: - Kconfig. Userspace should not rely on the presence or absence of any particular Kconfig symbol, in /proc/config.gz, in the copy of .config commonly installed to /boot, or in any invocation of the kernel build process. - Kernel-internal symbols. Do not rely on the presence, absence, location, or type of any kernel symbol, either in System.map files or the kernel binary itself. See Documentation/process/stable-api-nonsense.rst.