linux-kernel - Re: [RFC] regulator: Propagate voltage changes to supply regulators

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Message-ID: <20150930140747.GD7858@pengutronix.de>
Date:	Wed, 30 Sep 2015 16:07:47 +0200
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	linux-kernel@...r.kernel.org
Cc:	Mark Brown <broonie@...nel.org>,
	Liam Girdwood <lgirdwood@...il.com>, kernel@...gutronix.de,
	alkml@...gutronix.de
Subject: Re: [RFC] regulator: Propagate voltage changes to supply regulators

Please do not answer to this series, it contains a wrong address for the
linux-arm-kernel list. I just resent this with the correct addres. Sorry
for the noise.

Sascha

On Wed, Sep 30, 2015 at 03:57:48PM +0200, Sascha Hauer wrote:
> 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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