Re: [PATCH 06/14] regulator: axp20x: add software based soft_start for AXP209 LDO3

[Maxime Ripard <maxime.ripard@bootlin.com>]

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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.

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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