• Ruslan Bilovol's avatar
    usb: gadget: add f_uac1 variant based on a new u_audio api · 0591bc23
    Ruslan Bilovol authored
    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: default avatarRuslan Bilovol <ruslan.bilovol@gmail.com>
    Signed-off-by: default avatarFelipe Balbi <felipe.balbi@linux.intel.com>
    0591bc23
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