• Conversion of a number of CODEC drivers to use regmap directly. This is especially beneficial for drivers for devices which are part of MFDs as they can use a central cache for all operations and means that the process of factoring out the more complex register management code in ASoC can begin.
• As a result of the move of drivers to regmap the rbtree and LZO cache types have been removed, leaving only the the basic flat cache in ASoC. Drivers which need the more complex cache types should use regmap directly.
• Lots of cleanups and fixes from Axel Lin.
• New CODEC drivers for Cirrus CS42L73 and Realtek ALC5632.

• OpenFirmware bindings for the core and for the fixed regulator driver, contributed by Rajendra Nayak. Device tree bindings for the Freescale MC13892 PMIC were also added.
• A new regulator_bulk_force_disable() operation contributed by Donggeun Kim.
• A new driver for the Dialog DA9052 PMIC.

I’m strongly tempted to just block all of Yahoo! from the mail systems I control.

• 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.

switch (thing) {
case VALUE:
        /* Stuff */
        break;
case BAR:
        /* Nonsense */
        break;
default:
        /* Whatever */
        break;
}

with if statements instead:

if (thing == VALUE) {
        /* Stuff */
} else if (thing == BAR) {
        /* Nonsense */
} else {
        /* Whatever */
}

(where stuff, nonsense and whatever are usually a bit larger). I really don’t understand where this has come from – the if based form isn’t nearly so idiomatic for selecting between a range of values and this seems to have come from nowhere pretty much. Is there some code base out there where this is common practice or something?

• 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.

The version of this API in version 3.1 is very simple, just factoring out the simplest level of physical I/O from the devices. Devices register with the regmap API by providing a struct regmap_config (which currently only allows the sizes of the register addresses and values to be specified) and the bus-specific structure to it. They can then use simple read and write operations on the device:

int regmap_read(struct regmap *map, unsigned int reg, unsigned int *val);
int regmap_write(struct regmap *map, unsigned int reg, unsigned int val);

The API handles everything to do with formatting the data for transmission and parsing data coming back from the device. Block functions are also provided to allow multiple registers to be read or written simultaneously. Even with this basic level of support we end up saving quite a bit of code as drivers are converted to use the API.

The changes sitting in -next for version 3.2 take this a step further, adding support for more variations on SPI registers, a debugfs interface for dumping the device registers, register cache support courtesy of my colleague Dimitris Papastamos and trace points for dynamic instrumentation of the system.