Hi, this mail is copied from internal issue written in markdown - I hope this is still readable as mail. I am referring to kernel sources v4.9.87 but I think all my assumptions do still apply to current kernel versions. [regmap.h](https://elixir.bootlin.com/linux/v4.9.87/source/include/linux/regmap.h#L334) contains: ```c /** * Configuration for indirectly accessed or paged registers. * Registers, mapped to this virtual range, are accessed in two steps: * 1. page selector register update; * 2. access through data window registers. * * @name: Descriptive name for diagnostics * * @range_min: Address of the lowest register address in virtual range. * @range_max: Address of the highest register in virtual range. * * @page_sel_reg: Register with selector field. * @page_sel_mask: Bit shift for selector value. * @page_sel_shift: Bit mask for selector value. * * @window_start: Address of first (lowest) register in data window. * @window_len: Number of registers in data window. */ struct regmap_range_cfg { const char *name; /* Registers of virtual address range */ unsigned int range_min; unsigned int range_max; /* Page selector for indirect addressing */ unsigned int selector_reg; unsigned int selector_mask; int selector_shift; /* Data window (per each page) */ unsigned int window_start; unsigned int window_len; }; ``` Unfortunately this seems not to work for MMIO devices. In [`__regmap_init()`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap.c#L711) [`_regmap_bus_reg_read()`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap.c#L2330) is assigned to [`regmap.reg_read()`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/internal.h#L101) if `!bus->read || !bus->write`, else [`_regmap_bus_read()`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap.c#L2338) is assigned: ```c if (!bus) { map->reg_read = config->reg_read; map->reg_write = config->reg_write; map->defer_caching = false; goto skip_format_initialization; } else if (!bus->read || !bus->write) { map->reg_read = _regmap_bus_reg_read; map->reg_write = _regmap_bus_reg_write; map->defer_caching = false; goto skip_format_initialization; } else { map->reg_read = _regmap_bus_read; map->reg_update_bits = bus->reg_update_bits; } ``` [`_regmap_bus_reg_read()`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap.c#L2330) calls the `reg_read` function of the bus directly, [`_regmap_bus_read()`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap.c#L2338) instead calls `_regmap_raw_read()`: ```c static int _regmap_bus_reg_read(void *context, unsigned int reg, unsigned int *val) { struct regmap *map = context; return map->bus->reg_read(map->bus_context, reg, val); } static int _regmap_bus_read(void *context, unsigned int reg, unsigned int *val) { int ret; struct regmap *map = context; if (!map->format.parse_val) return -EINVAL; ret = _regmap_raw_read(map, reg, map->work_buf, map->format.val_bytes); if (ret == 0) *val = map->format.parse_val(map->work_buf); return ret; } ``` [`_regmap_raw_read()`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap.c#L2297) in turn calls [`_regmap_range_lookup()`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap-mmio.c#L479) and [`_regmap_select_page()`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap-mmio.c#L1283) which do the paging. - [`regmap_mmio`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap-mmio.c#L212) does neither contain `.read` nor `.write`. - [`regmap_i2c`](https://elixir.bootlin.com/linux/v4.9.87/source/drivers/base/regmap/regmap-i2c.c#L204) does contain both. My assumption is that paging is not a common use case for Memory-mapped I/O and thus has not been implemented for this case. - Are my assumptions correct? - If so, what would you recommend me to do: - Continue using `regmap-mmio` and implement my custom paging functions on top of that? - Enhance the current `regmap-mmio` implementation so it does paging and submit a patch? - Write my own `better-regmap-mmio` implementation? Thank you, Lars
