Regmap-based SPI driver example – putting it all together

All the steps involved in setting up Regmap, from configuration to device register access, can be enumerated as follows:

• Setting up a struct regmap_config object according to the device characteristics. Defining the register range if needed, default values if any, cache_type if needed, and so on. If custom read/write functions are needed, pass them to the reg_read/reg_write fields.
• In the probe function, allocating a register map using devm_regmap_init_i2c(), devm_regmap_init_spi(), or devm_regmap_init_mmio() depending on the connection with the underlying device – I2C, SPI, or memory-mapped.
• Whenever you need to read/write from/into registers, calling remap_[read|write] functions.
• When done with the register map, assuming you used resource-managed APIs, you have nothing else to do as devres core will take care of releasing the Regmap resources; otherwise, you'll have to call regmap_exit...