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[PATCH v2 0/2] regulator: Add support for parallel regulators

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  [PATCH v2 0/2] regulator: Add support for parallel regulators Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-01-12 14:40 +0100
    [PATCH v2 2/2] ARM: sunxi: chip: Add Wifi chip Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-01-12 14:40 +0100
    [PATCH v2 1/2] regulator: Add coupled regulator Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-01-12 14:40 +0100
      Re: [PATCH v2 1/2] regulator: Add coupled regulator Rob Herring <robh@kernel.org> - 2016-01-12 15:40 +0100
        Re: [PATCH v2 1/2] regulator: Add coupled regulator Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-01-15 10:00 +0100

#1307405 — [PATCH v2 0/2] regulator: Add support for parallel regulators

Hi,

On some boards, devices consuming a lot of power cannot use a single
regulator, but few of them in parallel to spread the consumption.

In such a case, we must ensure that all these regulators are kept in
sync.

Since this is something that is totally board specific, it should
obviously not be handle by each and every customer drivers that might
be driving a device wired this way on a particular board.

Instead, we implemented a regulator driver that just aggregates
several parent regulators and just forwards the regulators calls to
them.

Let me know what you think,
Maxime

Changes from v1:
  - Added documentation
  - Fixed an error in the is_enabled callback returned value
  - Unwind the enable and disable callbacks in case of a failure
  - Added a depency on CONFIG_OF
  - Added the missing module device table

Maxime Ripard (2):
  regulator: Add coupled regulator
  ARM: sunxi: chip: Add Wifi chip

 .../bindings/regulator/coupled-voltage.txt         |  18 ++
 arch/arm/boot/dts/sun5i-r8-chip.dts                |  44 ++-
 drivers/regulator/Kconfig                          |   8 +
 drivers/regulator/Makefile                         |   1 +
 drivers/regulator/coupled-voltage-regulator.c      | 299 +++++++++++++++++++++
 5 files changed, 369 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/devicetree/bindings/regulator/coupled-voltage.txt
 create mode 100644 drivers/regulator/coupled-voltage-regulator.c

-- 
2.6.4

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#1307406 — [PATCH v2 2/2] ARM: sunxi: chip: Add Wifi chip

The CHIP has a WiFi/BT chip on an SDIO bus. That controller is maintained
in reset through a GPIO and uses two independent regulators to be powered
that must be kept in sync.

Model this using an MMC power sequence and a coupled voltage regulator.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 arch/arm/boot/dts/sun5i-r8-chip.dts | 44 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/arch/arm/boot/dts/sun5i-r8-chip.dts b/arch/arm/boot/dts/sun5i-r8-chip.dts
index 530ab28e9ca2..b5ef4eb5b6b4 100644
--- a/arch/arm/boot/dts/sun5i-r8-chip.dts
+++ b/arch/arm/boot/dts/sun5i-r8-chip.dts
@@ -64,6 +64,24 @@
 	chosen {
 		stdout-path = "serial0:115200n8";
 	};
+
+	mmc0_pwrseq: mmc0_pwrseq {
+		compatible = "mmc-pwrseq-simple";
+		pinctrl-names = "default";
+		pinctrl-0 = <&chip_wifi_reg_on_pin>;
+		reset-gpios = <&pio 2 19 GPIO_ACTIVE_LOW>; /* PC19 */
+	};
+
+	/*
+	 * Both LDO3 and LDO4 are used in parallel to power up the
+	 * WiFi/BT Chip.
+	 */
+	vcc_wifi: wifi_reg {
+		compatible = "coupled-voltage-regulator";
+		regulator-name = "vcc-wifi";
+		vin0-supply = <&reg_ldo3>;
+		vin1-supply = <&reg_ldo4>;
+	};
 };
 
 &codec {
@@ -113,10 +131,15 @@
 	};
 };
 
+&mmc0_pins_a {
+	allwinner,pull = <SUN4I_PINCTRL_PULL_UP>;
+};
+
 &mmc0 {
 	pinctrl-names = "default";
 	pinctrl-0 = <&mmc0_pins_a>;
-	vmmc-supply = <&reg_vcc3v3>;
+	vmmc-supply = <&vcc_wifi>;
+	mmc-pwrseq = <&mmc0_pwrseq>;
 	bus-width = <4>;
 	non-removable;
 	status = "okay";
@@ -138,6 +161,13 @@
 		allwinner,pull = <SUN4I_PINCTRL_NO_PULL>;
 	};
 
+	chip_wifi_reg_on_pin: chip_wifi_reg_on_pin@0 {
+		allwinner,pins = "PC19";
+		allwinner,function = "gpio_out";
+		allwinner,drive = <SUN4I_PINCTRL_10_MA>;
+		allwinner,pull = <SUN4I_PINCTRL_NO_PULL>;
+	};
+
 	chip_id_det_pin: chip_id_det_pin@0 {
 		allwinner,pins = "PG2";
 		allwinner,function = "gpio_in";
@@ -171,6 +201,18 @@
 	regulator-always-on;
 };
 
+&reg_ldo3 {
+	regulator-min-microvolt = <3300000>;
+	regulator-max-microvolt = <3300000>;
+	regulator-name = "vcc-wifi-1";
+};
+
+&reg_ldo4 {
+	regulator-min-microvolt = <3300000>;
+	regulator-max-microvolt = <3300000>;
+	regulator-name = "vcc-wifi-2";
+};
+
 &reg_ldo5 {
 	regulator-min-microvolt = <1800000>;
 	regulator-max-microvolt = <1800000>;
-- 
2.6.4

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#1307407 — [PATCH v2 1/2] regulator: Add coupled regulator

Some boards, in order to power devices that have a quite high power
consumption, wire multiple regulators in parallel.

In such a case, the regulators need to be kept in sync, all of them being
enabled or disabled in parallel.

This also requires to expose only the voltages that are common to all the
regulators.

Eventually support for changing the voltage in parallel should be added
too, possibly with delays between each other to avoid having a too brutal
peak consumption.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
---
 .../bindings/regulator/coupled-voltage.txt         |  18 ++
 drivers/regulator/Kconfig                          |   8 +
 drivers/regulator/Makefile                         |   1 +
 drivers/regulator/coupled-voltage-regulator.c      | 299 +++++++++++++++++++++
 4 files changed, 326 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/regulator/coupled-voltage.txt
 create mode 100644 drivers/regulator/coupled-voltage-regulator.c

diff --git a/Documentation/devicetree/bindings/regulator/coupled-voltage.txt b/Documentation/devicetree/bindings/regulator/coupled-voltage.txt
new file mode 100644
index 000000000000..f5401aab52f2
--- /dev/null
+++ b/Documentation/devicetree/bindings/regulator/coupled-voltage.txt
@@ -0,0 +1,18 @@
+Coupled voltage regulators
+
+Required properties:
+- compatible		: Must be "coupled-voltage-regulator".
+
+Optional properties:
+- vinX-supply		: Phandle to the regulators it aggregates
+
+Any property defined as part of the core regulator binding defined in
+regulator.txt can also be used.
+
+Example:
+	vcc_wifi: wifi_reg {
+		compatible = "coupled-voltage-regulator";
+		regulator-name = "vcc-wifi";
+		vin0-supply = <&reg_ldo3>;
+		vin1-supply = <&reg_ldo4>;
+	};
diff --git a/drivers/regulator/Kconfig b/drivers/regulator/Kconfig
index 7df9da82f592..5d18c9a6169f 100644
--- a/drivers/regulator/Kconfig
+++ b/drivers/regulator/Kconfig
@@ -35,6 +35,14 @@ config REGULATOR_FIXED_VOLTAGE
 	  useful for systems which use a combination of software
 	  managed regulators and simple non-configurable regulators.
 
+config REGULATOR_COUPLED_VOLTAGE
+	tristate "Coupled voltage regulator support"
+	depends on OF
+	help
+	  This driver provides support for regulators that are an
+	  aggregate of other regulators in the system, and need to
+	  keep them all in sync.
+
 config REGULATOR_VIRTUAL_CONSUMER
 	tristate "Virtual regulator consumer support"
 	help
diff --git a/drivers/regulator/Makefile b/drivers/regulator/Makefile
index 980b1943fa81..76c9728113f7 100644
--- a/drivers/regulator/Makefile
+++ b/drivers/regulator/Makefile
@@ -22,6 +22,7 @@ obj-$(CONFIG_REGULATOR_AS3711) += as3711-regulator.o
 obj-$(CONFIG_REGULATOR_AS3722) += as3722-regulator.o
 obj-$(CONFIG_REGULATOR_AXP20X) += axp20x-regulator.o
 obj-$(CONFIG_REGULATOR_BCM590XX) += bcm590xx-regulator.o
+obj-$(CONFIG_REGULATOR_COUPLED_VOLTAGE) += coupled-voltage-regulator.o
 obj-$(CONFIG_REGULATOR_DA903X)	+= da903x.o
 obj-$(CONFIG_REGULATOR_DA9052)	+= da9052-regulator.o
 obj-$(CONFIG_REGULATOR_DA9055)	+= da9055-regulator.o
diff --git a/drivers/regulator/coupled-voltage-regulator.c b/drivers/regulator/coupled-voltage-regulator.c
new file mode 100644
index 000000000000..c1bf798abfef
--- /dev/null
+++ b/drivers/regulator/coupled-voltage-regulator.c
@@ -0,0 +1,299 @@
+/*
+ * Copyright 2015 Free Electrons
+ * Copyright 2015 NextThing Co.
+ *
+ * Author: Maxime Ripard <maxime.ripard@free-electrons.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ */
+
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+#include <linux/regulator/consumer.h>
+#include <linux/regulator/driver.h>
+#include <linux/regulator/of_regulator.h>
+
+#define COUPLED_REGULATOR_MAX_SUPPLIES	16
+
+/**
+ * struct coupled_regulator - Private data for the driver
+ * @regulators: array of struct regulator aggregated
+ * @n_regulators: number of regulators aggregated
+ * @voltages: array of voltages common to all the regulators
+ * @n_voltages: number of common voltages
+ */
+struct coupled_regulator {
+	struct regulator	**regulators;
+	int			n_regulators;
+	int			*voltages;
+	int			n_voltages;
+};
+
+static int coupled_regulator_disable(struct regulator_dev *rdev)
+{
+	struct coupled_regulator *creg = rdev_get_drvdata(rdev);
+	int ret, i;
+
+	for (i = 0; i < creg->n_regulators; i++) {
+		ret = regulator_disable(creg->regulators[i]);
+		if (ret) {
+			dev_warn(&rdev->dev, "Couldn't disable our regulator\n");
+			goto err_unwind;
+		}
+	}
+
+	return 0;
+
+err_unwind:
+	/*
+	 * In case a regulator cannot disable, unwind everything to
+	 * make sure we're in a consistent (and probably safe) state
+	 */
+	for (; i >= 0; i--) {
+		int en_ret = regulator_enable(creg->regulators[i]);
+		if (en_ret)
+			dev_warn(&rdev->dev,
+				 "Couldn't unwind disable operation for our regulator\n");
+	}
+
+	return ret;
+}
+
+static int coupled_regulator_enable(struct regulator_dev *rdev)
+{
+	struct coupled_regulator *creg = rdev_get_drvdata(rdev);
+	int ret, i;
+
+	for (i = 0; i < creg->n_regulators; i++) {
+		ret = regulator_enable(creg->regulators[i]);
+		if (ret) {
+			dev_warn(&rdev->dev, "Couldn't enable our regulator\n");
+			goto err_unwind;
+		}
+	}
+
+	return 0;
+
+err_unwind:
+	/*
+	 * In case a regulator cannot enable, unwind everything to
+	 * make sure we're in a consistent (and probably safe) state
+	 */
+	for (; i >= 0; i--) {
+		int en_ret = regulator_disable(creg->regulators[i]);
+		if (en_ret)
+			dev_warn(&rdev->dev,
+				 "Couldn't unwind enable operation for our regulator\n");
+	}
+
+	return ret;
+}
+
+static int coupled_regulator_is_enabled(struct regulator_dev *rdev)
+{
+	struct coupled_regulator *creg = rdev_get_drvdata(rdev);
+	int i;
+
+	for (i = 0; i < creg->n_regulators; i++) {
+		int ret = regulator_is_enabled(creg->regulators[i]);
+
+		/*
+		 * If there's at least one regulator that isn't
+		 * enabled or returns an error, return that,
+		 * otherwise, just go on.
+		 */
+		if (ret <= 0)
+			return ret;
+	}
+
+	return 1;
+}
+
+static int coupled_regulator_list_voltage(struct regulator_dev *rdev,
+					  unsigned int selector)
+{
+	struct coupled_regulator *creg = rdev_get_drvdata(rdev);
+
+	if (selector >= creg->n_voltages)
+		return -EINVAL;
+
+	return creg->voltages[selector];
+}
+
+static struct regulator_ops coupled_regulator_ops = {
+	.enable			= coupled_regulator_enable,
+	.disable		= coupled_regulator_disable,
+	.is_enabled		= coupled_regulator_is_enabled,
+	.list_voltage		= coupled_regulator_list_voltage,
+};
+
+static struct regulator_desc coupled_regulator_desc = {
+	.name		= "coupled-voltage-regulator",
+	.type		= REGULATOR_VOLTAGE,
+	.ops		= &coupled_regulator_ops,
+	.owner		= THIS_MODULE,
+};
+
+static int coupled_regulator_probe(struct platform_device *pdev)
+{
+	const struct regulator_init_data *init_data;
+	struct coupled_regulator *creg;
+	struct regulator_config config = { };
+	struct regulator_dev *regulator;
+	struct regulator_desc *desc;
+	struct device_node *np = pdev->dev.of_node;
+	int max_voltages, i;
+
+	if (!np) {
+		dev_err(&pdev->dev, "Device Tree node missing\n");
+		return -EINVAL;
+	}
+
+	creg = devm_kzalloc(&pdev->dev, sizeof(*creg), GFP_KERNEL);
+	if (!creg)
+		return -ENOMEM;
+
+	init_data = of_get_regulator_init_data(&pdev->dev, np,
+					       &coupled_regulator_desc);
+	if (!init_data)
+		return -ENOMEM;
+
+	config.of_node = np;
+	config.dev = &pdev->dev;
+	config.driver_data = creg;
+	config.init_data = init_data;
+
+	for (i = 0; i < COUPLED_REGULATOR_MAX_SUPPLIES; i++) {
+		char *propname = kasprintf(GFP_KERNEL, "vin%d-supply", i);
+		const void *prop = of_get_property(np, propname, NULL);
+		kfree(propname);
+
+		if (!prop) {
+			creg->n_regulators = i;
+			break;
+		}
+	}
+
+	dev_dbg(&pdev->dev, "Found %d parent regulators\n",
+		creg->n_regulators);
+
+	if (!creg->n_regulators) {
+		dev_err(&pdev->dev, "No parent regulators listed\n");
+		return -EINVAL;
+	}
+
+	creg->regulators = devm_kcalloc(&pdev->dev, creg->n_regulators,
+					sizeof(*creg->regulators), GFP_KERNEL);
+	if (!creg->regulators)
+		return -ENOMEM;
+
+	for (i = 0; i < creg->n_regulators; i++) {
+		char *propname = kasprintf(GFP_KERNEL, "vin%d", i);
+
+		dev_dbg(&pdev->dev, "Trying to get supply %s\n", propname);
+
+		creg->regulators[i] = devm_regulator_get(&pdev->dev, propname);
+		kfree(propname);
+
+		if (IS_ERR(creg->regulators[i])) {
+			dev_err(&pdev->dev, "Couldn't get regulator vin%d\n",
+				i);
+			return PTR_ERR(creg->regulators[i]);
+		}
+
+		/*
+		 * FIXME: We should probably be doing something
+		 * smarter here to avoid having a bunch of regulators
+		 * disabled and a bunch enabled.
+		 */
+		if (regulator_is_enabled(creg->regulators[i])) {
+			int ret = regulator_enable(creg->regulators[i]);
+			if (ret) {
+				regulator_put(creg->regulators[i]);
+				return ret;
+			}
+		}
+	}
+
+	/*
+	 * Since we want only to expose voltages that can be set on
+	 * all the regulators, we won't have more voltages supported
+	 * than the number of voltages supported by the first
+	 * regulator in our list
+	 */
+	max_voltages = regulator_count_voltages(creg->regulators[0]);
+
+	creg->voltages = devm_kcalloc(&pdev->dev, max_voltages, sizeof(int),
+				      GFP_KERNEL);
+
+	/* Build up list of supported voltages */
+	for (i = 0; i < max_voltages; i++) {
+		int voltage = regulator_list_voltage(creg->regulators[0], i);
+		bool usable = true;
+		int j;
+
+		if (voltage <= 0)
+			continue;
+
+		dev_dbg(&pdev->dev, "Checking voltage %d...\n", voltage);
+
+		for (j = 1; j < creg->n_regulators; j++) {
+			if (!regulator_is_supported_voltage(creg->regulators[j],
+							    voltage, voltage)) {
+				usable = false;
+				break;
+			}
+		}
+
+		if (usable) {
+			creg->voltages[creg->n_voltages++] = voltage;
+			dev_dbg(&pdev->dev,
+				 "Adding voltage %d to the list of supported voltages\n",
+				 voltage);
+		}
+	}
+
+	dev_dbg(&pdev->dev, "Supporting %d voltages\n", creg->n_voltages);
+
+	desc = devm_kmemdup(&pdev->dev, &coupled_regulator_desc,
+			    sizeof(coupled_regulator_desc), GFP_KERNEL);
+	if (!desc)
+		return -ENOMEM;
+	desc->n_voltages = creg->n_voltages;
+
+	regulator = devm_regulator_register(&pdev->dev, desc, &config);
+	if (IS_ERR(regulator)) {
+		dev_err(&pdev->dev, "Failed to register regulator %s\n",
+			coupled_regulator_desc.name);
+		return PTR_ERR(regulator);
+	}
+
+	return 0;
+}
+
+static struct of_device_id coupled_regulator_of_match[] = {
+	{ .compatible = "coupled-voltage-regulator" },
+	{ /* Sentinel */ },
+};
+MODULE_DEVICE_TABLE(of, coupled_regulator_of_match);
+
+static struct platform_driver coupled_regulator_driver = {
+	.probe	= coupled_regulator_probe,
+
+	.driver = {
+		.name		= "coupled-voltage-regulator",
+		.of_match_table	= coupled_regulator_of_match,
+	},
+};
+module_platform_driver(coupled_regulator_driver);
+
+MODULE_AUTHOR("Maxime Ripard <maxime.ripard@free-electrons.com>");
+MODULE_DESCRIPTION("Coupled Regulator Driver");
+MODULE_LICENSE("GPL");
-- 
2.6.4

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#1307484 — Re: [PATCH v2 1/2] regulator: Add coupled regulator

On Tue, Jan 12, 2016 at 02:37:21PM +0100, Maxime Ripard wrote:
> Some boards, in order to power devices that have a quite high power
> consumption, wire multiple regulators in parallel.
> 
> In such a case, the regulators need to be kept in sync, all of them being
> enabled or disabled in parallel.
> 
> This also requires to expose only the voltages that are common to all the
> regulators.
> 
> Eventually support for changing the voltage in parallel should be added
> too, possibly with delays between each other to avoid having a too brutal
> peak consumption.
> 
> Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> ---
>  .../bindings/regulator/coupled-voltage.txt         |  18 ++
>  drivers/regulator/Kconfig                          |   8 +
>  drivers/regulator/Makefile                         |   1 +
>  drivers/regulator/coupled-voltage-regulator.c      | 299 +++++++++++++++++++++
>  4 files changed, 326 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/regulator/coupled-voltage.txt
>  create mode 100644 drivers/regulator/coupled-voltage-regulator.c
> 
> diff --git a/Documentation/devicetree/bindings/regulator/coupled-voltage.txt b/Documentation/devicetree/bindings/regulator/coupled-voltage.txt
> new file mode 100644
> index 000000000000..f5401aab52f2
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/regulator/coupled-voltage.txt
> @@ -0,0 +1,18 @@
> +Coupled voltage regulators
> +
> +Required properties:
> +- compatible		: Must be "coupled-voltage-regulator".
> +
> +Optional properties:
> +- vinX-supply		: Phandle to the regulators it aggregates
> +
> +Any property defined as part of the core regulator binding defined in
> +regulator.txt can also be used.
> +
> +Example:
> +	vcc_wifi: wifi_reg {
> +		compatible = "coupled-voltage-regulator";
> +		regulator-name = "vcc-wifi";
> +		vin0-supply = <&reg_ldo3>;
> +		vin1-supply = <&reg_ldo4>;
> +	};

Why not just make ?-supply a list of phandles? That would be simpler 
than a virtual regulator.

Rob

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#1309966 — Re: [PATCH v2 1/2] regulator: Add coupled regulator

[Multipart message — attachments visible in raw view] — view raw

Hi Rob,

On Tue, Jan 12, 2016 at 08:31:00AM -0600, Rob Herring wrote:
> On Tue, Jan 12, 2016 at 02:37:21PM +0100, Maxime Ripard wrote:
> > Some boards, in order to power devices that have a quite high power
> > consumption, wire multiple regulators in parallel.
> > 
> > In such a case, the regulators need to be kept in sync, all of them being
> > enabled or disabled in parallel.
> > 
> > This also requires to expose only the voltages that are common to all the
> > regulators.
> > 
> > Eventually support for changing the voltage in parallel should be added
> > too, possibly with delays between each other to avoid having a too brutal
> > peak consumption.
> > 
> > Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
> > ---
> >  .../bindings/regulator/coupled-voltage.txt         |  18 ++
> >  drivers/regulator/Kconfig                          |   8 +
> >  drivers/regulator/Makefile                         |   1 +
> >  drivers/regulator/coupled-voltage-regulator.c      | 299 +++++++++++++++++++++
> >  4 files changed, 326 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/regulator/coupled-voltage.txt
> >  create mode 100644 drivers/regulator/coupled-voltage-regulator.c
> > 
> > diff --git a/Documentation/devicetree/bindings/regulator/coupled-voltage.txt b/Documentation/devicetree/bindings/regulator/coupled-voltage.txt
> > new file mode 100644
> > index 000000000000..f5401aab52f2
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/regulator/coupled-voltage.txt
> > @@ -0,0 +1,18 @@
> > +Coupled voltage regulators
> > +
> > +Required properties:
> > +- compatible		: Must be "coupled-voltage-regulator".
> > +
> > +Optional properties:
> > +- vinX-supply		: Phandle to the regulators it aggregates
> > +
> > +Any property defined as part of the core regulator binding defined in
> > +regulator.txt can also be used.
> > +
> > +Example:
> > +	vcc_wifi: wifi_reg {
> > +		compatible = "coupled-voltage-regulator";
> > +		regulator-name = "vcc-wifi";
> > +		vin0-supply = <&reg_ldo3>;
> > +		vin1-supply = <&reg_ldo4>;
> > +	};
> 
> Why not just make ?-supply a list of phandles? That would be simpler 
> than a virtual regulator.

I'm not sure I get what you're saying. Do you want to remove that
driver entirely, or just allow the -supply properties in the device
tree to take a list?

In the former case, the rationale behind this driver is that the
regulators powering a device also have to be kept in sync, both by
enabling and disabling all of them at once, but also by all having
them at the same voltages.

We could push that code in the consumer drivers, but that has some
significant drawbacks:
  - That would duplicate that code in all the drivers, leading to the
    usual drawbacks of code duplication, especially when it's not
    really trivial to handle (or at least, when there's a few
    gotchas).
  - When you come to consider it from an hardware point of view, the
    device usually have a single pin that powers it. It's the board
    designer that chose to route that pin to multiple regulators, so
    it's really the board that is wired that way, and putting that
    code in the consumer drivers would be an abstraction leak imho.
  - We might not even have a driver for these regulators, or at least
    one that play by the rules. In our case, that's an out-of-tree
    WiFi driver.

In the latter case, I remember Mark saying several times that he was
not in favour of such a change, even recently:
https://lkml.org/lkml/2015/10/14/238

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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