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The firmware for the Raspberry PI already supports simultanous output of audio through both the HDMI and the Headphone jack. The current implementation of ALSA doesn't expose this well to user mode since the firmware audio is represented as a single card. A newer approach is taken here and a virtual card is created for each output(HDMI, Headphones, and Traditional ALSA). The firmware has the concept of channels or streams for which the number to use is passed in the device tree. These streams are allocated to each of the virtual cards. As a side effect of this change, since each output is represented independenly it's now very easy to use PulseAudio to control the priorities of the outputs. Testing: Audacity and VLC were both loaded at the same time. Each application was assigned to a different card. With this change I was able to play different music files at the same time through the HDMI and Headphones jacks and control the audio independently. Signed-off-by: Michael Zoran <mzoran@crowfest.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.