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

[Milo Kim]

Hi Paul,

On 29/12/15 20:13, Paul Kocialkowski wrote:
> Hi Milo,
>
> Le mardi 29 dÃcembre 2015 Ã 09:45 +0900, Milo Kim a Ãcrit :
> > Hi Paul,
> >
> > On 29/12/15 07:49, Paul Kocialkowski wrote:
> > > Hi Milo, thanks for the review,
> > >
> > > Le lundi 28 dÃcembre 2015 Ã 09:56 +0900, Milo Kim a Ãcrit :
> > > > 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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