From 9ca8dbcc65cfc63d6f5ef3312a33184e1d726e00 Mon Sep 17 00:00:00 2001 From: Yunhong Jiang Date: Tue, 4 Aug 2015 12:17:53 -0700 Subject: Add the rt linux 4.1.3-rt3 as base Import the rt linux 4.1.3-rt3 as OPNFV kvm base. It's from git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-4.1.y-rt and the base is: commit 0917f823c59692d751951bf5ea699a2d1e2f26a2 Author: Sebastian Andrzej Siewior Date: Sat Jul 25 12:13:34 2015 +0200 Prepare v4.1.3-rt3 Signed-off-by: Sebastian Andrzej Siewior We lose all the git history this way and it's not good. We should apply another opnfv project repo in future. Change-Id: I87543d81c9df70d99c5001fbdf646b202c19f423 Signed-off-by: Yunhong Jiang --- kernel/Documentation/sound/alsa/soc/overview.txt | 95 ++++++++++++++++++++++++ 1 file changed, 95 insertions(+) create mode 100644 kernel/Documentation/sound/alsa/soc/overview.txt (limited to 'kernel/Documentation/sound/alsa/soc/overview.txt') diff --git a/kernel/Documentation/sound/alsa/soc/overview.txt b/kernel/Documentation/sound/alsa/soc/overview.txt new file mode 100644 index 000000000..ff88f52ee --- /dev/null +++ b/kernel/Documentation/sound/alsa/soc/overview.txt @@ -0,0 +1,95 @@ +ALSA SoC Layer +============== + +The overall project goal of the ALSA System on Chip (ASoC) layer is to +provide better ALSA support for embedded system-on-chip processors (e.g. +pxa2xx, au1x00, iMX, etc) and portable audio codecs. Prior to the ASoC +subsystem there was some support in the kernel for SoC audio, however it +had some limitations:- + + * Codec drivers were often tightly coupled to the underlying SoC + CPU. This is not ideal and leads to code duplication - for example, + Linux had different wm8731 drivers for 4 different SoC platforms. + + * There was no standard method to signal user initiated audio events (e.g. + Headphone/Mic insertion, Headphone/Mic detection after an insertion + event). These are quite common events on portable devices and often require + machine specific code to re-route audio, enable amps, etc., after such an + event. + + * Drivers tended to power up the entire codec when playing (or + recording) audio. This is fine for a PC, but tends to waste a lot of + power on portable devices. There was also no support for saving + power via changing codec oversampling rates, bias currents, etc. + + +ASoC Design +=========== + +The ASoC layer is designed to address these issues and provide the following +features :- + + * Codec independence. Allows reuse of codec drivers on other platforms + and machines. + + * Easy I2S/PCM audio interface setup between codec and SoC. Each SoC + interface and codec registers its audio interface capabilities with the + core and are subsequently matched and configured when the application + hardware parameters are known. + + * Dynamic Audio Power Management (DAPM). DAPM automatically sets the codec to + its minimum power state at all times. This includes powering up/down + internal power blocks depending on the internal codec audio routing and any + active streams. + + * Pop and click reduction. Pops and clicks can be reduced by powering the + codec up/down in the correct sequence (including using digital mute). ASoC + signals the codec when to change power states. + + * Machine specific controls: Allow machines to add controls to the sound card + (e.g. volume control for speaker amplifier). + +To achieve all this, ASoC basically splits an embedded audio system into +multiple re-usable component drivers :- + + * Codec class drivers: The codec class driver is platform independent and + contains audio controls, audio interface capabilities, codec DAPM + definition and codec IO functions. This class extends to BT, FM and MODEM + ICs if required. Codec class drivers should be generic code that can run + on any architecture and machine. + + * Platform class drivers: The platform class driver includes the audio DMA + engine driver, digital audio interface (DAI) drivers (e.g. I2S, AC97, PCM) + and any audio DSP drivers for that platform. + + * Machine class driver: The machine driver class acts as the glue that + decribes and binds the other component drivers together to form an ALSA + "sound card device". It handles any machine specific controls and + machine level audio events (e.g. turning on an amp at start of playback). + + +Documentation +============= + +The documentation is spilt into the following sections:- + +overview.txt: This file. + +codec.txt: Codec driver internals. + +DAI.txt: Description of Digital Audio Interface standards and how to configure +a DAI within your codec and CPU DAI drivers. + +dapm.txt: Dynamic Audio Power Management + +platform.txt: Platform audio DMA and DAI. + +machine.txt: Machine driver internals. + +pop_clicks.txt: How to minimise audio artifacts. + +clocking.txt: ASoC clocking for best power performance. + +jack.txt: ASoC jack detection. + +DPCM.txt: Dynamic PCM - Describes DPCM with DSP examples. -- cgit 1.2.3-korg