regmap: add configurable downshift for addresses

Add an additional reg_downshift to be applied to register addresses before
any register accesses. An example of a device that uses this is a VSC7514
chip, which require each register address to be downshifted by two if the
access is performed over a SPI bus.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Link: https://lore.kernel.org/r/20220313224524.399947-2-colin.foster@in-advantage.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: colin-foster-in-advantage

drivers/base/regmap/internal.h

@@ -31,6 +31,7 @@ struct regmap_format {
 	size_t buf_size;
 	size_t reg_bytes;
 	size_t pad_bytes;
+	size_t reg_downshift;
 	size_t val_bytes;
 	void (*format_write)(struct regmap *map,
 			     unsigned int reg, unsigned int val);

drivers/base/regmap/regmap.c

@@ -823,6 +823,7 @@ struct regmap *__regmap_init(struct device *dev,
 
 	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;
 	map->format.val_bytes = DIV_ROUND_UP(config->val_bits, 8);
 	map->format.buf_size = DIV_ROUND_UP(config->reg_bits +
 			config->val_bits + config->pad_bits, 8);
@@ -1735,6 +1736,7 @@ static int _regmap_raw_write_impl(struct regmap *map, unsigned int reg,
 			return ret;
 	}
 
+	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,
 				      map->write_flag_mask);
@@ -1905,6 +1907,7 @@ static int _regmap_bus_formatted_write(void *context, unsigned int reg,
 			return ret;
 	}
 
+	reg >>= map->format.reg_downshift;
 	map->format.format_write(map, reg, val);
 
 	trace_regmap_hw_write_start(map, reg, 1);
@@ -2346,6 +2349,7 @@ 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->format.reg_downshift;
 		map->format.format_reg(u8, reg, map->reg_shift);
 		u8 += reg_bytes + pad_bytes;
 		map->format.format_val(u8, val, 0);
@@ -2673,6 +2677,7 @@ static int _regmap_raw_read(struct regmap *map, unsigned int reg, void *val,
 			return ret;
 	}
 
+	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,
 				      map->read_flag_mask);

include/linux/regmap.h

@@ -237,6 +237,8 @@ typedef void (*regmap_unlock)(void *);
  * @reg_stride: The register address stride. Valid register addresses are a
  *              multiple of this value. If set to 0, a value of 1 will be
  *              used.
+ * @reg_downshift: The number of bits to downshift the register before
+ *		   performing any operations.
  * @pad_bits: Number of bits of padding between register and value.
  * @val_bits: Number of bits in a register value, mandatory.
  *
@@ -360,6 +362,7 @@ struct regmap_config {
 
 	int reg_bits;
 	int reg_stride;
+	int reg_downshift;
 	int pad_bits;
 	int val_bits;