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

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Message-ID: <568323B7.7080101@ti.com>
Date:	Wed, 30 Dec 2015 09:22:15 +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 20:13, Paul Kocialkowski wrote:
> Hi Milo,
>
> Le mardi 29 décembre 2015 à 09:45 +0900, Milo Kim a écrit :
>> 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.
>
> Well, I really don't understand why the EN pin would turn on/off the
> chip. All it does it enable the regulators outputs (by entering IDLE
> mode), the serial block is already available in STANDBY state.
>
> If we want some regulators enabled at boot, the best thing to do seems
> to be to request the GPIO with the GPIOF_INIT_HIGH flag, as done in e.g.
> the max8952 regulator driver:
>
> 	if (pdata->reg_data->constraints.boot_on)
> 		config.ena_gpio_flags |= GPIOF_OUT_INIT_HIGH;

According to MAX8952 datasheet, output regulator is enabled/disabled 
using EN pin, so ena_gpio is used correctly.
However, LP8720/5 regulators are enabled/disabled through I2C command. 
Only few regulators of LP8725 can be on/off by separate external pins. 
(B2_EN and LDO3_EN)
Please note that EN pin in LP8720/5 is not the control pin for 
enabling/disabling regulators.

Best regards,
Milo
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