linux-kernel - Re: [PATCH 4/6] regulator: lp872x: Add enable GPIO pin support

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Date:	Tue, 29 Dec 2015 09:45:28 +0900
From:	Milo Kim <milo.kim@...com>
To:	Paul Kocialkowski <contact@...lk.fr>
CC:	Mark Brown <broonie@...nel.org>, <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Benoît Cousson <bcousson@...libre.com>,
	Tony Lindgren <tony@...mide.com>,
	Liam Girdwood <lgirdwood@...il.com>,
	<devicetree@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-omap@...r.kernel.org>
Subject: Re: [PATCH 4/6] regulator: lp872x: Add enable GPIO pin support

Hi Paul,

On 29/12/15 07:49, Paul Kocialkowski wrote:
> Hi Milo, thanks for the review,
>
> Le lundi 28 décembre 2015 à 09:56 +0900, Milo Kim a écrit :
>> Hi Paul,
>>
>> On 23/12/15 20:56, Mark Brown wrote:
>>> On Wed, Dec 23, 2015 at 11:58:37AM +0100, Paul Kocialkowski wrote:
>>>
>>>> +	gpio = lp->pdata->enable_gpio;
>>>> +	if (!gpio_is_valid(gpio))
>>>> +		return 0;
>>>> +
>>>> +	/* Always set enable GPIO high. */
>>>> +	ret = devm_gpio_request_one(lp->dev, gpio, GPIOF_OUT_INIT_HIGH, "LP872X EN");
>>>> +	if (ret) {
>>>> +		dev_err(lp->dev, "gpio request err: %d\n", ret);
>>>> +		return ret;
>>>> +	}
>>>
>>> This isn't really adding support for the enable GPIO as the changelog
>>> suggests, it's requesting but not managing the GPIO.  Since there is
>>> core support for manging enable GPIOs this seems especially silly,
>>> please tell the core about the GPIO and then it will work at runtime
>>> too.
>>>
>>
>> With reference to my previous mail, external GPIOs for LDO3 and BUCK2 in
>> LP8725 can be specified through regulator_config.ena_gpio. BUCK2 only
>> can be controlled by external pin when CONFIG pin is grounded.
>>
>> Please see the description at page 5 of the datasheet.
>>
>> 	http://www.ti.com/lit/ds/symlink/lp8725.pdf
>
> After reading the datasheets thoroughly, it seems to me that for the
> lp8720, the EN pin is used to enable the regulators output, which is a
> good fit for the core regulator GPIO framework, as there is no reason to
> keep it on when no regulator is in use. The serial interface is already
> available when EN=0 and regulators can be configured in that state. The
> lp8725 seems seems to behave the same when CONFIG=0 (the datasheet
> clearly states: "CONFIG=0: EN=1 turns on outputs or standby mode if
> EN=0"). On the other hand, it is indeed used as a power-on pin when
> CONFIG=1.

I think it's different use case. LP8720/5 are designed for system PMU, 
so some regulators are enabled by default after the device is on. EN pin 
is used for turning on/off the chip. This pin does not control regulator 
outputs directly. It's separate functional block in the silicon.

On the other hand, 'ena_gpio' is used for each regulator control itself.
For example, WM8994 has two LDOs which are controlled by external pins. 
LDOs are enabled/disabled through LDO1ENA and LDO2ENA pins. In this 
case, 'ena_gpio' is used.

	http://www.cirrus.com/en/pubs/proDatasheet/WM8994_v4.4.pdf
	(please refer to page 224 and 225)

Best regards,
Milo
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