I have a problem with the ADAU1761 (although the problem I would think would manifest itself with a veriety of codecs).

The register values are cached to minimize the number of writes needed, and there is a set of default values specified. However, this assumes that when the software boots the chip is always in the default state. This is not necessarily the case, because the chip has no external reset line and resets its internal state using an internal power-on-reset circuit, so if the system is rebooted without a power cycle, the regcache will contain the default values of the registers, whereas the actual registers in the chip will retain their previous values. Hence, if attempting to set a value in a register which is in fact identical to the default value, it will not be written, and the value that is currently in the register will remain. This can lead to all sorts of misconfigurations, depending on the previous state of the chip.

One way to fix this is simply to avoid setting up a set of default registers (looking at regcache.c, one way seems to be to omit setting the reg_defaults and num_reg_defaults members of the struct regmap_config during initialization, and instead setting num_reg_defaults_raw to the number of registers the chip has, but not setting reg_defaults_raw; I don't know if this is how it is intended to be used however). The regcache framework will then read all the register values from the chip and use them as the new defaults.

While this would seem to be technically correct, the question is if this is acceptable? A drawback is that there will be a lot of I2C or SPI accesses just to get the default values. Or should the caching behavior at startup be configured in some way, for instance via devicetree?

/Ricard