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Date:   Tue, 4 Dec 2018 13:31:44 +0000
From:   Priit Laes <plaes@plaes.org>
To:     Maxime Ripard <maxime.ripard@bootlin.com>
Cc:     Lee Jones <lee.jones@linaro.org>, Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Chen-Yu Tsai <wens@csie.org>,
        Sebastian Reichel <sre@kernel.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Mark Brown <broonie@kernel.org>, devicetree@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-pm@vger.kernel.org, Olliver Schinagl <oliver@schinagl.nl>
Subject: Re: [PATCH 06/14] regulator: axp20x: add software based soft_start
 for AXP209 LDO3
Message-ID: <20181204133144.eqd3dk3jgqm4fbk4@plaes.org>
References: <cover.156212c9c5df493e098556cad9793a07dcab5e32.1543245984.git-series.plaes@plaes.org>
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On Tue, Nov 27, 2018 at 10:36:19AM +0100, Maxime Ripard wrote:
> On Mon, Nov 26, 2018 at 05:27:47PM +0200, Priit Laes wrote:
> > From: Olliver Schinagl <oliver@schinagl.nl>
> > 
> > In the past, there have been words on various lists that if LDO3 is
> > disabled in u-boot, but enabled in the DTS, the axp209 driver would
> > fail to continue/hang. Several enable/disable patches have been
> > issues to devicetree's in both the kernel and u-boot to address
> > this issue.
> > 
> > What really happened however, was that the AXP209 shuts down without
> > a notice and without setting an interrupt. This is caused when LDO3
> > gets overloaded, for example with large capacitors on the LDO3 output.
> > 
> > Normally, we would expect that AXP209 would source 200 mA as per
> > datasheet and set and trigger an interrupt when being overloaded.
> > For some reason however, this does not happen.
> > 
> > As a work-around, we use the soft-start constraint of the regulator
> > node to first bring up the LDO3 to the lowest possible voltage and
> > then enable the LDO. After that, we can set the requested voltage
> > as usual.
> > 
> > Combining this setting with the regulator-ramp-delay allows LDO3 to
> > enable voltage slowly and staggered, potentially reducing overall
> > inrush current.
> > 
> > Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
> > Signed-off-by: Priit Laes <plaes@plaes.org>
> > ---
> >  drivers/regulator/axp20x-regulator.c | 57 ++++++++++++++++++++++++++++-
> >  1 file changed, 56 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/regulator/axp20x-regulator.c b/drivers/regulator/axp20x-regulator.c
> > index 1d9fa62..e8a895b 100644
> > --- a/drivers/regulator/axp20x-regulator.c
> > +++ b/drivers/regulator/axp20x-regulator.c
> > @@ -14,6 +14,7 @@
> >   */
> >  
> >  #include <linux/bitops.h>
> > +#include <linux/delay.h>
> >  #include <linux/err.h>
> >  #include <linux/init.h>
> >  #include <linux/mfd/axp20x.h>
> > @@ -23,6 +24,7 @@
> >  #include <linux/platform_device.h>
> >  #include <linux/regmap.h>
> >  #include <linux/regulator/driver.h>
> > +#include <linux/regulator/machine.h>
> >  #include <linux/regulator/of_regulator.h>
> >  
> >  #define AXP20X_GPIO0_FUNC_MASK		GENMASK(3, 0)
> > @@ -430,6 +432,59 @@ static int axp20x_set_ramp_delay(struct regulator_dev *rdev, int ramp)
> >  	return regmap_update_bits(axp20x->regmap, reg, mask, cfg);
> >  }
> >  
> > +static int axp20x_regulator_enable_regmap(struct regulator_dev *rdev)
> > +{
> > +	struct axp20x_dev *axp20x = rdev_get_drvdata(rdev);
> > +	const struct regulator_desc *desc = rdev->desc;
> > +
> > +	if (!rdev)
> > +		return -EINVAL;
> > +
> > +	switch (axp20x->variant) {
> > +	case AXP209_ID:
> > +		if ((desc->id == AXP20X_LDO3) &&
> > +		    rdev->constraints && rdev->constraints->soft_start) {
> > +			int v_out;
> > +			int ret;
> > +
> > +			/*
> > +			 * On some boards, the LDO3 can be overloaded when
> > +			 * turning on, causing the entire PMIC to shutdown
> > +			 * without warning. Turning it on at the minimal voltage
> > +			 * and then setting the voltage to the requested value
> > +			 * works reliably.
> > +			 */
> > +			if (regulator_is_enabled_regmap(rdev))
> > +				break;
> > +
> > +			v_out = regulator_get_voltage_sel_regmap(rdev);
> > +			if (v_out < 0)
> > +				return v_out;
> > +
> > +			if (v_out == 0)
> > +				break;
> > +
> > +			ret = regulator_set_voltage_sel_regmap(rdev, 0x00);
> > +			/*
> > +			 * A small pause is needed between
> > +			 * setting the voltage and enabling the LDO to give the
> > +			 * internal state machine time to process the request.
> > +			 */
> > +			usleep_range(1000, 5000);
> > +			ret |= regulator_enable_regmap(rdev);
> > +			ret |= regulator_set_voltage_sel_regmap(rdev, v_out);
> > +
> > +			return ret;
> > +		}
> > +		break;
> > +	default:
> > +		/* No quirks */
> > +		break;
> > +	}
> > +
> > +	return regulator_enable_regmap(rdev);
> > +};
> > +
> 
> This is some pretty generic code, and could be useful to some other
> users. I guess a generic function would be better for this.

Yes, makes sense. Although, should we then also distinguish between
regulators which support soft-start in hardware and devices which emulate
it by delay, like in this case?


P?ikest,
Priit