regmap: Add precious registers to the driver interface

Some devices are sensitive to reads on their registers, especially for
things like clear on read interrupt status registers. Avoid creating
problems with these with things like debugfs by allowing drivers to tell
the core about them. If a register is marked as precious then the core
will not internally generate any reads of it.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

include/linux/regmap.h

@@ -33,6 +33,9 @@ struct spi_device;
  *                     can be read from.
  * @volatile_register: Optional callback returning true if the register
  *                     value can't be cached.
+ * @precious_register: Optional callback returning true if the rgister
+ *                     should not be read outside of a call from the driver
+ *                     (eg, a clear on read interrupt status register).
  */
 struct regmap_config {
 	int reg_bits;
@@ -42,6 +45,7 @@ struct regmap_config {
 	bool (*writeable_reg)(struct device *dev, unsigned int reg);
 	bool (*readable_reg)(struct device *dev, unsigned int reg);
 	bool (*volatile_reg)(struct device *dev, unsigned int reg);
+	bool (*precious_reg)(struct device *dev, unsigned int reg);
 };
 
 typedef int (*regmap_hw_write)(struct device *dev, const void *data,