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[RFC] regulator: Propagate voltage changes to supply regulators

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  [RFC] regulator: Propagate voltage changes to supply regulators Sascha Hauer <s.hauer@pengutronix.de> - 2015-09-30 16:10 +0200
    [PATCH 1/6] Revert "regulator: core: Handle full constraints systems when resolving supplies" Sascha Hauer <s.hauer@pengutronix.de> - 2015-09-30 16:10 +0200
      Re: [PATCH 1/6] Revert "regulator: core: Handle full constraints  systems when resolving supplies" Mark Brown <broonie@kernel.org> - 2015-09-30 20:10 +0200

#1236338 — [RFC] regulator: Propagate voltage changes to supply regulators

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. This
patch adds support for such a scenario.

A new min_dropout_uv field is added to struct regulator_desc. Regulators
can specify the minimun dropout voltage they need for proper function
here. Now when the voltage is changed on a regulator the regulator core
makes sure that
a) before increasing the voltage on the current regulator the supply
   provides at least the desired voltage plus the minimum dropout
b) after decreasing the voltage on the current regulator the supply
   is optimized to the minimum required voltage within the needs of
   the consumers of the supply.

Calculating the optimum voltage for the supply regulator is a bit tricky
since the simple approach of just adding the desired minimum voltage and
the minimum dropout is not enough. It may happen that the current
regulator does not support the desired minimum voltage, but only a
higher one. This means we have to figure out the lowest voltage
supported by the regulator that is higher than the minimum desired
voltage. The regulator_get_voltage_floor introduced with this series
does
exactly that.

This is a first RFC for this series which probably has some rough edges,
but it was already tested successfully on a Phytec PFLA02 i.MX6 board.

Please review, any input welcome.

Sascha

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#1236340 — [PATCH 1/6] Revert "regulator: core: Handle full constraints systems when resolving supplies"

This reverts commit 9f7e25edb1575a6d2363dc003f9cc09d840657e2.

When a regulator A is registered and is supplied by regulator B which is
not yet registered then a regulator_get on regulator A will set the As
supply to the dummy regulator. This is not correct, we should return
-EPROBE_DEFER instead as done without this patch.
Of course reverting this patch brings back the issue it fixed, so this
is not a solution, but what is the correct solution?

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
---
 drivers/regulator/core.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 7849187..bd9db70 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -1403,13 +1403,9 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
 			return 0;
 		}
 
-		if (have_full_constraints()) {
-			r = dummy_regulator_rdev;
-		} else {
-			dev_err(dev, "Failed to resolve %s-supply for %s\n",
-				rdev->supply_name, rdev->desc->name);
-			return -EPROBE_DEFER;
-		}
+		dev_err(dev, "Failed to resolve %s-supply for %s\n",
+			rdev->supply_name, rdev->desc->name);
+		return -EPROBE_DEFER;
 	}
 
 	/* Recursively resolve the supply of the supply */
-- 
2.5.3

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#1236603 — Re: [PATCH 1/6] Revert "regulator: core: Handle full constraints systems when resolving supplies"

[Multipart message — attachments visible in raw view] — view raw

On Wed, Sep 30, 2015 at 04:05:41PM +0200, Sascha Hauer wrote:
> This reverts commit 9f7e25edb1575a6d2363dc003f9cc09d840657e2.
> 
> When a regulator A is registered and is supplied by regulator B which is
> not yet registered then a regulator_get on regulator A will set the As
> supply to the dummy regulator. This is not correct, we should return
> -EPROBE_DEFER instead as done without this patch.

What makes you say this is not correct?  In a system with fully
specified supplies if we fail to resolve the supply we know that no
supply will ever appear and so substitute in the dummy on the assumption
that there is a supply with no software control.

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