regmap: allow upshifting register addresses before performing operations

Similar to the existing reg_downshift mechanism, that is used to
translate register addresses on busses that have a smaller address
stride, it's also possible to want to upshift register addresses.

Such a case was encountered when network PHYs and PCS that usually sit
on a MDIO bus (16-bits register with a stride of 1) are integrated
directly as memory-mapped devices. Here, the same register layout
defined in 802.3 is used, but the register now have a larger stride.

Introduce a mechanism to also allow upshifting register addresses.
Re-purpose reg_downshift into a more generic, signed reg_shift, whose
sign indicates the direction of the shift. To avoid confusion, also
introduce macros to explicitly indicate if we want to downshift or
upshift.

For bisectability, change any use of reg_downshift to use reg_shift.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Tested-by: Colin Foster <colin.foster@in-advantage.com>
Link: https://lore.kernel.org/r/20230407152604.105467-1-maxime.chevallier@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>

1 files changed, 12 insertions, 3 deletions

diff --git a/include/linux/regmap.h b/include/linux/regmap.h
index 8743b177399e..c2b9cc5db824 100644
--- a/include/linux/regmap.h
+++ b/include/linux/regmap.h
@@ -46,6 +46,14 @@ struct sdw_slave;
 #define REGMAP_MDIO_C45_DEVAD_MASK	GENMASK(20, 16)
 #define REGMAP_MDIO_C45_REGNUM_MASK	GENMASK(15, 0)
 
+/*
+ * regmap.reg_shift indicates by how much we must shift registers prior to
+ * performing any operation. It's a signed value, positive numbers means
+ * downshifting the register's address, while negative numbers means upshifting.
+ */
+#define REGMAP_UPSHIFT(s)	(-(s))
+#define REGMAP_DOWNSHIFT(s)	(s)
+
 /* An enum of all the supported cache types */
 enum regcache_type {
 	REGCACHE_NONE,
@@ -246,8 +254,9 @@ 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.
+ * @reg_shift: The number of bits to shift the register before performing any
+ *	       operations. Any positive number will be downshifted, and negative
+ *	       values will be upshifted
  * @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.
@@ -381,7 +390,7 @@ struct regmap_config {
 
 	int reg_bits;
 	int reg_stride;
-	int reg_downshift;
+	int reg_shift;
 	unsigned int reg_base;
 	int pad_bits;
 	int val_bits;