regmap: allow a defined reg_base to be added to every address

There's an inconsistency that arises when a register set can be accessed
internally via MMIO, or externally via SPI. The VSC7514 chip allows both
modes of operation. When internally accessed, the system utilizes __iomem,
devm_ioremap_resource, and devm_regmap_init_mmio.

For SPI it isn't possible to utilize memory-mapped IO. To properly operate,
the resource base must be added to the register before every operation.
Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Link: https://lore.kernel.org/r/20220313224524.399947-3-colin.foster@in-advantage.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/internal.h

@@ -63,6 +63,7 @@ struct regmap {
 	regmap_unlock unlock;
 	void *lock_arg; /* This is passed to lock/unlock functions */
 	gfp_t alloc_flags;
+	unsigned int reg_base;
 
 	struct device *dev; /* Device we do I/O on */
 	void *work_buf;     /* Scratch buffer used to format I/O */

drivers/base/regmap/regmap.c

@@ -821,6 +821,8 @@ struct regmap *__regmap_init(struct device *dev,
 	else
 		map->alloc_flags = GFP_KERNEL;
 
+	map->reg_base = config->reg_base;
+
 	map->format.reg_bytes = DIV_ROUND_UP(config->reg_bits, 8);
 	map->format.pad_bytes = config->pad_bits / 8;
 	map->format.reg_downshift = config->reg_downshift;
@@ -1736,6 +1738,7 @@ static int _regmap_raw_write_impl(struct regmap *map, unsigned int reg,
 			return ret;
 	}
 
+	reg += map->reg_base;
 	reg >>= map->format.reg_downshift;
 	map->format.format_reg(map->work_buf, reg, map->reg_shift);
 	regmap_set_work_buf_flag_mask(map, map->format.reg_bytes,
@@ -1907,6 +1910,7 @@ static int _regmap_bus_formatted_write(void *context, unsigned int reg,
 			return ret;
 	}
 
+	reg += map->reg_base;
 	reg >>= map->format.reg_downshift;
 	map->format.format_write(map, reg, val);
 
@@ -2349,6 +2353,7 @@ static int _regmap_raw_multi_reg_write(struct regmap *map,
 		unsigned int reg = regs[i].reg;
 		unsigned int val = regs[i].def;
 		trace_regmap_hw_write_start(map, reg, 1);
+		reg += map->reg_base;
 		reg >>= map->format.reg_downshift;
 		map->format.format_reg(u8, reg, map->reg_shift);
 		u8 += reg_bytes + pad_bytes;
@@ -2677,6 +2682,7 @@ static int _regmap_raw_read(struct regmap *map, unsigned int reg, void *val,
 			return ret;
 	}
 
+	reg += map->reg_base;
 	reg >>= map->format.reg_downshift;
 	map->format.format_reg(map->work_buf, reg, map->reg_shift);
 	regmap_set_work_buf_flag_mask(map, map->format.reg_bytes,

include/linux/regmap.h

@@ -239,6 +239,8 @@ typedef void (*regmap_unlock)(void *);
  *              used.
  * @reg_downshift: The number of bits to downshift the register before
  *		   performing any operations.
+ * @reg_base: Value to be added to every register address before performing any
+ *	      operation.
  * @pad_bits: Number of bits of padding between register and value.
  * @val_bits: Number of bits in a register value, mandatory.
  *
@@ -363,6 +365,7 @@ struct regmap_config {
 	int reg_bits;
 	int reg_stride;
 	int reg_downshift;
+	unsigned int reg_base;
 	int pad_bits;
 	int val_bits;