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

From: Milo Kim <milo.kim@ti.com>
To: Paul Kocialkowski <contact@paulk.fr>
Cc: "Mark Rutland" <mark.rutland@arm.com>,
	devicetree@vger.kernel.org,
	"Russell King" <linux@arm.linux.org.uk>,
	"Pawel Moll" <pawel.moll@arm.com>,
	"Ian Campbell" <ijc+devicetree@hellion.org.uk>,
	"Tony Lindgren" <tony@atomide.com>,
	linux-kernel@vger.kernel.org, "Rob Herring" <robh+dt@kernel.org>,
	"Liam Girdwood" <lgirdwood@gmail.com>,
	"Mark Brown" <broonie@kernel.org>,
	"Benoît Cousson" <bcousson@baylibre.com>,
	"Kumar Gala" <galak@codeaurora.org>,
	linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 4/6] regulator: lp872x: Add enable GPIO pin support
Date: Tue, 29 Dec 2015 09:45:28 +0900	[thread overview]
Message-ID: <5681D7A8.2030101@ti.com> (raw)
In-Reply-To: <1451342963.14631.13.camel@collins>

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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