Since we need to read voltages of parents as part of setting supply
voltages we need to be able to do get_voltage() internally without
taking locks so reorganize the locking to take locks on the full tree on
entry rather than as we recurse when called externally.

Reported-by: John Stultz <john.stultz@linaro.org>
Tested-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Until now changing the voltage of a regulator only ever effected the
regulator itself, but never its supplies. It's a common pattern though
to put LDO regulators behind switching regulators. The switching
regulators efficiently drop the input voltage but have a high ripple on
their output. The output is then cleaned up by the LDOs. For higher
energy efficiency the voltage drop at the LDOs should be minimized. For
this scenario we need to propagate the voltage change to the supply
regulators. Another scenario where voltage propagation is desired is
a regulator which only consists of a switch and thus cannot regulate
voltages itself. In this case we can pass setting voltages to the
supply.

This patch adds support for voltage propagation. We do voltage
propagation when the current regulator has a minimum dropout voltage
specified or if the current regulator lacks a get_voltage operation
(indicating it's a switch and not a regulator).

Changing the supply voltage must be done carefully. When we are
increasing the current regulators output we must first increase the
supply voltage and then the regulator itself. When we are decreasing the
current regulators voltage we must decrease the supply voltage after
changing the current regulators voltage.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

_regulator_call_set_voltage has code to translate a minimum/maximum
voltage pair into a selector. This code is useful for others aswell,
so create a regulator_map_voltage function.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

The unlocked version will be needed when we start propagating voltage
changes to the supply regulators.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

The unlocked version will be needed when we start propagating voltage
changes to the supply regulators.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

Each regulator_dev is locked with its own mutex. This is fine as long
as only one regulator_dev is locked, but makes lockdep unhappy when we
have to walk up the supply chain like it can happen in
regulator_get_voltage:

regulator_get_voltage ->
 mutex_lock(&regulator->rdev->mutex) ->
_regulator_get_voltage(regulator->rdev) ->
regulator_get_voltage(rdev->supply) ->
mutex_lock(&regulator->rdev->mutex);

This causes lockdep to issue a possible deadlock warning.

There are at least two ways to work around this:

- We can always lock the whole supply chain using the functions
  introduced with this patch.
- We could store the current voltage in struct regulator_rdev so
  that we do not have to walk up the supply chain for the
  _regulator_get_voltage case.

Anyway, regulator_lock_supply/regulator_unlock_supply will be needed
once we allow regulator_set_voltage to optimize the supply voltages.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

When resolving regulator-regulator supplies we ignore probe deferral
returns from regulator_dev_lookup() (such as are generated for DT when
we can see a supply is registered) and just fall back to the dummy
regulator if there are full constraints (as is the case for DT).  This
means that probe deferral is broken for DT systems, fix that by paying
attention to -EPROBE_DEFER return codes like we do -ENODEV.

A further patch will simplify this further, this is a minimal fix for
the specific issue.

Fixes: 9f7e25edb1575a6d2 (regulator: core: Handle full constraints systems when resolving supplies)
Reported-by: Sascha Hauer <s.hauer@pengutronix.de>
Tested-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Mark Brown <broonnie@kernel.org>
Cc: stable@vger.kernel.org