• Support for register caches – Dimitris Papastamos ported his code for rbtree and LZO caches from ASoC over to regmap. This makes it easy for drivers to cache the current values of the device registers, improving performance by eliminating reads when doing read/modify/write cycles and providing functions to restore the register cache when resuming from power down. An indexed cache type was also added but this will be removed in 3.3 as it offers no real advantage over rbtree.
• Support for a wider range of SPI register transfer formats contributed by Lars-Peter Clausen.
• Tracepoints supporting both register access logging and monitoring of the time spent on register I/O operations.
• Register map dumps via debugfs to help provide diagnostic information during development.

• Substantial optimization of the DAPM algorithm, substantially reducing the CPU usage when power states change. This is especially beneficial with larger modern devices.
• Support for CODEC drivers using the regmap API.
• Some smaller API updates – support for larger register maps, support for specifying a source when setting a sysclk.
• New CPU drivers for Alchemy and Freescale MXS.
• New CODEC drivers for Analog ADAU1373, Realtek RT5631 and Wolfson Microelectronics WM1811 and WM5100.

• Lots of cleanups to the register cache code in preparation for moving the code to the regmap API.
• Support for maintaining lower power when in mostly idle states like microphone detection.
• Support for weak DAPM routes, enabling better pop/click performance for paths like sidetones.
• New CODEC drivers for Analog Devices ADAV80x, Sigmatel STA32x and Wolfson WM8728 and WM8983.

• Support DAPM controls that affect multiple paths – mainly used for single register bits that affect the routing for a stereo pair of audio streams.
• Simplifications in the cache infrastructure.
• New machine drivers for iPAQ hx4700, PCM hookup for WM8580 on Samsung reference platforms and Wolfson Speyside, plus a generalization of the Tegra Harmony driver to cover a range of other platforms based off a similar reference design.
• New CODEC drivers for AK4641, MAX98095 and WM8996.

• Support for registering machine drivers as first class devices rather than using the soc-audio device. Support for the soc-audio device will be removed at some point in the future.
• Support for ordering widget power changes within widget types, helping with large CODECs and multi-stage amplifiers.
• Support for waiting for multiple slow events to complete during DAPM sequences, making it easier to handle things like DC offset correction on multiple outputs.
• CPU support for Intel Medfield and nVidia Tegra2.
• CODEC support for Cirrus CS4271, Freescale SGTL5000, Maxim MAX8950, National Semiconductors LM4857, TI SN95031 and Wolfson WM8991
• Machine support for Intel Medfield MID reference platforms, nVidia Harmony, and Visstrim M10.

• Enhancements to multi-component from Jarkko Nikula allowing multiple devices of the same type to be included in one system (and handling other overlaps between devices) and support cross device DAPM.
• Support from Dimitris Papastamos for compressing the register cache in memory using either an rbtree or LZO, giving substantial memory savings on CODECs with large register maps, especially those that are sparse. This is especially beneficial to modern devices with integrated DSPs. This can be enabled by machine drivers, though CODECs can also provide defaults.
• Addition of trace points around DAPM and register I/O operation, allowing very low overhead logging without interfering with the main system log, useful for collecting verbose diagnostics without interfering with system operation and for always enabled flight recorder style tracking for intermittent problems. I blogged about ASoC trace points in more detail at the time.
• Restructuring of the Samsung CPU support from Jassi Brar, including a number of really good usability improvements. This supports features of more modern CPUs such as the ability to run two audio streams to a single I2S port and includes a number of API simplifications which should also make developing drivers for Samsung systems much easier.
• New CODEC drivers for ALC5621/2/3, WM8737, WM8770 and WM8958.
• Machine support for HP iPAQ H1940, HP t5325 thin clients and OpenRC Ultimate.

There’s a bunch of existing documentation out there for the trace subsystem, including some in the kernel under Documentation/trace, which I won’t repeat here. The ASoC events are grouped together under ‘asoc’. The raw log can be viewed by looking at the file tracing/trace in debugfs. Here’s a sample output from starting playback of an MP3 on a Samsung SMDK6410 reference system using WM8580, a high performance six channel CODEC with a very simple software interface:

mplayer-1673  [000]   183.920000: snd_soc_dapm_start: card=SMDK-I2S
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=Rear val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=Center+Sub val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=Front val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=VOUT3R val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=VOUT3L val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=VOUT2R val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=VOUT2L val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=VOUT1R val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=VOUT1L val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=DAC3 val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=DAC2 val=1
mplayer-1673  [000]   183.920000: snd_soc_dapm_widget_power: widget=DAC1 val=1
mplayer-1673  [000]   183.920000: snd_soc_bias_level_start: card=SMDK-I2S val=2
mplayer-1673  [000]   183.920000: snd_soc_bias_level_done: card=SMDK-I2S val=2
mplayer-1673  [000]   183.920000: snd_soc_reg_read: codec=wm8580-codec.0-001b.27 reg=32 val=1e
mplayer-1673  [000]   183.920000: snd_soc_reg_write: codec=wm8580-codec.0-001b.27 reg=32 val=2
mplayer-1673  [000]   183.920000: snd_soc_bias_level_start: card=SMDK-I2S val=3
mplayer-1673  [000]   183.920000: snd_soc_bias_level_done: card=SMDK-I2S val=3
mplayer-1673  [000]   183.920000: snd_soc_dapm_done: card=SMDK-I2S
mplayer-1673  [000]   183.920000: snd_soc_reg_read: codec=wm8580-codec.0-001b.27 reg=13 val=10
mplayer-1673  [000]   183.920000: snd_soc_reg_write: codec=wm8580-codec.0-001b.27 reg=13 val=0

Each line represents a trace event, showing the process that initiated the event, the CPU it ran on and the time it was recorded at together with event-specific details. On this system the time is reported with 10ms accuracy and the CODEC is very simple so the timing information is not terribly informative, but more accurate timers can be really helpful in analysing what’s going on with more complex CODECs. The set of events available will change over time, the key ones currently present in the kernel are:

• snd_soc_dapm_start and snd_soc_dapm_done: These events show the start and stop of the DAPM algorithms, showing the time spent on power management decisions.
• snd_soc_dapm_widget_power events are generated for each of the widgets which DAPM has determined needs to change state. The ‘val=1′ means that all these widgets are being powered up, val=0 would show power down.
• snd_soc_reg_write events show values written to registers.
• snd_soc_reg_read events show values read from registers – these reads may be done from the register cache, or may be from the hardware.
• snd_soc_dapm_widget_event_start and snd_soc_dapm_widget_event_done show the time spent in per-widget event callbacks.

The set of events traced will change as the subsystem develops and as people gain more experience with using the trace API.

• Overhaul of the core APIs for registration of all kinds of devices from my co-maintainer Liam Girdwood, reducing the level of direct coupling between machine drivers and their CODEC and CPU drivers allowing ASoC machines to have multiple CODEC devices and multiple instances of the same CODEC device within a system.
• New CODEC drivers for  88PM860x CODEC, MAX98088/9, WL1273, WM8962, WM8804, and WM8985.
• New CPU drivers for EP93xx AC’97 controllers, MPC85xx SSI ports, and SH HDMI controllers.
• Machine support for Freescale P1022 DS, Marvell Tavor and Saarb and Simplemachines Sim.One

• Support for keeping audio paths through the CODEC up during system suspend, primarily intended for use with devices where the Linux system is one of several independent systems running on the device and the other systems (like the cellular modem in a phone) can maintain useful audio paths even when the Linux system is inactive.
• Enhancements to the jack detection infrastructure, including the addition of notifiers on jack status changes (allowing better integration of physical jack detection with electronic methods) and snd_soc_dapm_force_enable_pin() (which allows DAPM managed supplies such as microphone biases to be forced on). For example, jack status change notifications can be used to enable microphone detection via bias current sense only when a microphone is physically present.
• Support for knot and continuous PCM rates in the core.
• SMDK6410 5.1 audio support, TI SDP4030 audio support, and basic support for playback on the 1133-EV1 PMIC module for Freescale i.MX31ADS systems (currently limited by the support for the SSI interface on the i.MX31).
• Support for DaVinci integrated voice CODECs, Philips UDA1345 CODEC, SuperH FSI2 interfaces, TI OMAP4, TWL6040 CODECs, WM9090 audio subsystem.