Introduction to regmap and its data structures – I2C, SPI, and MMIO

Regmap is an abstraction register access mechanism provided by the Linux kernel that mainly targets SPI, I2C, and memory-mapped registers.

APIs in this framework are bus agnostic and handle the underlying configuration under the hood. That being said, the main data structure in this framework is struct regmap_config, defined in include/linux/regmap.h in the kernel source tree as follows:

struct regmap_config {
   const char *name;
   int reg_bits;
   int reg_stride;
   int pad_bits;
   int val_bits;
   bool (*writeable_reg)(struct device *dev, unsigned int reg);
   bool (*readable_reg)(struct device *dev, unsigned int reg);
   bool (*volatile_reg)(struct device *dev, unsigned int reg);
   bool (*precious_reg)(struct device *dev, unsigned int reg);
   int...