Hi Jan, On 08/28/2018 04:02 PM, Jan Kundrát wrote: > On sobota 25. srpna 2018 18:11:17 CEST, Andrew Lunn wrote: >>> Explicitely initializing all registers sounds reasonable. Should work >>> even on unusual i2c designs. >> >> And it is not so hard to do. There are 30 writable registers on the 16 >> LED variant. But a lot of them are identical, one per LED. > > I looked at regmap, and I am confused by its regmap_defaults and the > notion of a cache. I would like to just add some default values and let > the regmap infrastructure copy them into the device for me. I'm not a regmap expert, but have looked into its internals several times and this is how I understand it: - the purpose of regmap cache is to minimize the I2C traffic on the bus - this is especially vital in case of regmap_update_bits(), which without the cache would incur an additional I2C readout to get the current register state - of course it also allows to avoid redundant register updates, that wouldn't change its state Regarding reg_defaults the doc says: * @reg_defaults: Power on reset values for registers (for use with * register cache support). In your case you'd need to initialize this array with the register values you want, and then call regcache_sync(). > > - Is this supported by the regmap core? > > - Do I need to enable some regmap cache for this? (Probably a flat one.) Right, REGCACHE_FLAT is reasonable choice in case of relatively small amount of registers. > - Are there some side effects of the regmap cache? A little bit greater memory usage, and time overhead due to the need for finding relevant cache entry. This can be however alleviated by using rbtree cache. I haven't looked at what REGCACHE_COMPRESSED offers. > I'm asking because the documentation in the .h files does not answer > these questions for me. Analysis of drivers/base/regmap directory contents allows to gain more understanding in this matter. -- Best regards, Jacek Anaszewski
