regulator: Add helpers for low-level register access

Add helper functions that allow regulator consumers to obtain low-level
details about the regulator hardware, like the voltage selector register
address and such. These details can be useful when configuring hardware
or firmware that want to do low-level access to regulators, with no
involvement from the kernel.

The use-case for Tegra is a voltage-controlled oscillator clocksource
which has control logic to change the supply voltage via I2C to achieve
a desired output clock rate.

Signed-off-by: Tuomas Tynkkynen <ttynkkynen@nvidia.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/Documentation/power/regulator/consumer.txt b/Documentation/power/regulator/consumer.txt
index 55c4175d8099..81c0e2b49cd8 100644
--- a/Documentation/power/regulator/consumer.txt
+++ b/Documentation/power/regulator/consumer.txt
@@ -180,3 +180,38 @@ int regulator_unregister_notifier(struct regulator *regulator,
 
 Regulators use the kernel notifier framework to send event to their interested
 consumers.
+
+7. Regulator Direct Register Access
+===================================
+Some kinds of power management hardware or firmware are designed such that
+they need to do low-level hardware access to regulators, with no involvement
+from the kernel. Examples of such devices are:
+
+- clocksource with a voltage-controlled oscillator and control logic to change
+  the supply voltage over I2C to achieve a desired output clock rate
+- thermal management firmware that can issue an arbitrary I2C transaction to
+  perform system poweroff during overtemperature conditions
+
+To set up such a device/firmware, various parameters like I2C address of the
+regulator, addresses of various regulator registers etc. need to be configured
+to it. The regulator framework provides the following helpers for querying
+these details.
+
+Bus-specific details, like I2C addresses or transfer rates are handled by the
+regmap framework. To get the regulator's regmap (if supported), use :-
+
+struct regmap *regulator_get_regmap(struct regulator *regulator);
+
+To obtain the hardware register offset and bitmask for the regulator's voltage
+selector register, use :-
+
+int regulator_get_hardware_vsel_register(struct regulator *regulator,
+					 unsigned *vsel_reg,
+					 unsigned *vsel_mask);
+
+To convert a regulator framework voltage selector code (used by
+regulator_list_voltage) to a hardware-specific voltage selector that can be
+directly written to the voltage selector register, use :-
+
+int regulator_list_hardware_vsel(struct regulator *regulator,
+				 unsigned selector);