linux-kernel - Re: regulator: ab8500: ambiguous meaning of delay setting in struct ab8500_regulator

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Date:	Wed, 27 Mar 2013 08:58:26 +0100
From:	Bengt Jönsson <bengt.g.jonsson@...ricsson.com>
To:	Axel Lin <axel.lin@...ics.com>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Lee Jones <lee.jones@...aro.org>,
	Yvan FILLION <yvan.fillion@...ricsson.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: regulator: ab8500: ambiguous meaning of delay setting in struct
 ab8500_regulator_info

On 03/27/2013 01:15 AM, Axel Lin wrote:
> Hi,
>
> The comment of struct ab8500_regulator_info says the delay means
> "startup/set voltage delay in us".
> I'm confused by the meaning, does it mean enable_time or set_voltage_time_sel
> time or both?
>
>   * @enable_time: Time taken for the regulator voltage output voltage to
>   *               stabilise after being enabled, in microseconds.
>
>   * @set_voltage_time_sel: Time taken for the regulator voltage output voltage
>   *               to stabilise after being set to a new value, in microseconds.
>   *               The function provides the from and to voltage selector, the
>   *               function should return the worst case.
The data sheet does not specify time delay for voltage selection, only 
enable time. So I have assumed the same time for voltage selection.
> Current code only has delay setting for AB8500_LDO_TVOUT, it looks like it
> means enable_time rather than the delay for set_voltage_time_sel.
> (well, AB8500_LDO_TVOUT is fixed voltage, it does not implement set_voltage_time_sel)
>
> ab8500_regulator_set_voltage_time_sel() returns info->delay, but all it's users
> (AB8500_LDO_AUX1, AB8500_LDO_AUX2, AB8500_LDO_AUX3, AB8500_LDO_INTCORE)
> do not has delay setting. ( So now ab8500_regulator_set_voltage_time_sel returns 0. )
This is a flaw in the driver. It should specify delay for all 
regulators, not just VTVout.

Worst case enable time from data sheet:
Vana: enable time = 140 us
Vaux1/2: enable time = 200 us
Vaux3: enable time = 450 us
Vintcore: enable time = 750 us
Vamic1/2: enable time = 500 us
Vdmic: enable time = 420 us
VTVout: enable time = 500 us
Vaudio: enable time = 140 us
Vusb: enable time = 150 us
>
> Axel
>
Thanks for looking into it.

Bengt
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