linux-kernel - [RFC PATCH 0/2] cpufreq/regulator: Limit minimum voltage only

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Date:	Fri, 19 Apr 2013 14:55:52 +0300
From:	Taras Kondratiuk <taras@...com>
To:	<lgirdwood@...il.com>, <broonie@...nel.org>, <rjw@...k.pl>,
	<viresh.kumar@...aro.org>, <shawn.guo@...aro.org>
CC:	<cpufreq@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, Taras Kondratiuk <taras@...com>
Subject: [RFC PATCH 0/2] cpufreq/regulator: Limit minimum voltage only

Using a "voltage tolerance" for doing DVFS is not a proper way.
It leads to a few issues:
- voltage is limited to a narrow range near OPP voltage,
  so other consumers of the same regulator can't set their own constraints
  if they don't overlap with this narrow range. No ganged rails :(
- usually OPP voltage is an absolute minimum voltage
  necessary for correct work (not taking into account AVS).
  Applying plus/minus tolerance can lead to an unstable device.
  For example omap-cpufreq has 4% tolerance configured,
  so for OMAP4430 MPU OPP50 we get 0.984V instead of 1.025V. 

This series adds a new API to regulator FW to limit only minimum voltage.
As example API is used for cpufreq-cpu0, but if it is accepted I'll fix
other drivers (omap-cpufreq, imx6q-cpufreq, etc).
Maybe regulator_set_voltage_tol() should be removed completely,
because it started to be used in a wrong way.
  
Patches are based on v3.9-rc7.
I've tested them on v3.8 based branch on OMAP4430 Blaze board.

Taras Kondratiuk (2):
  regulator: core: Add regulator_set_voltage_min()
  cpufreq: cpufreq-cpu0: Limit minimum voltage only

 drivers/cpufreq/cpufreq-cpu0.c     |   12 ++++--------
 include/linux/regulator/consumer.h |    6 ++++++
 2 files changed, 10 insertions(+), 8 deletions(-)

-- 
1.7.9.5

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