[RESEND PATCH v3 1/2] power: supply: add input voltage limit property

[RESEND PATCH v3 1/2] power: supply: add input voltage limit property

[Enric Balletbo i Serra]

This is part of the Pixel C's thermal management strategy to effectively
limit the input power to 5V 3A when the screen is on. When the screen is
on, the display, the CPU, and the GPU all contribute more heat to the
system than while the screen is off, and we made a tradeoff to throttle
the charger in order to give more of the thermal budget to those other
components.

So there's nothing fundamentally broken about the hardware that would
cause the Pixel C to malfunction if we were charging at 9V or 12V instead
of 5V when the screen is on, ie if userspace doesn't change this.

What would happen is that you wouldn't meet Google's skin temperature
targets on the system if the charger was allowed to run at 9V or 12V with
the screen on.

For folks hacking on Pixel Cs (which is now outside of Google's official
support window for Android) and customizing their own kernel and userspace
this would be acceptable, but we wanted to expose this feature in the
power supply properties because the feature does exist in the Emedded
Controller firmware of the Pixel C and all of Google's Chromebooks with
USB-C made since 2015 in case someone running an up to date kernel wanted
to limit the charging power for thermal or other reasons.

This patch exposes a new property, similar to input current limit, to
re-configure the maximum voltage from the external supply at runtime
based on system-level knowledge or user input.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
Acked-by: Adam Thomson <Adam.Thomson.Opensource@diasemi.com>
---

Changes in v3:
- Improve commit log and documentation with Benson comments.

Changes in v2:
- Document the new property in ABI/testing/sysfs-class-power.
- Add the Reviewed-by Guenter Roeck tag.

 Documentation/ABI/testing/sysfs-class-power | 15 +++++++++++++++
 Documentation/power/power_supply_class.txt  |  2 ++
 drivers/power/supply/power_supply_sysfs.c   |  1 +
 include/linux/power_supply.h                |  1 +
 4 files changed, 19 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-class-power b/Documentation/ABI/testing/sysfs-class-power
index 5e23e22dce1b..6dee5c105a28 100644
--- a/Documentation/ABI/testing/sysfs-class-power
+++ b/Documentation/ABI/testing/sysfs-class-power
@@ -335,6 +335,21 @@ Description:
 		Access: Read, Write
 		Valid values: Represented in microamps
 
+What:		/sys/class/power_supply/<supply_name>/input_voltage_limit
+Date:		Nov 2018
+Contact:	linux-pm@vger.kernel.org
+Description:
+		This entry configures the incoming VBUS voltage limit currently
+		set in the supply. Normally this is configured based on
+		system-level knowledge or user input (e.g. This is part of the
+		Pixel C's thermal management strategy to effectively limit the
+		input power to 5V when the screen is on to meet Google's skin
+		temperature targets). Note that this feature should not be
+		used for safety critical things.
+
+		Access: Read, Write
+		Valid values: Represented in microvolts
+
 What:		/sys/class/power_supply/<supply_name>/online,
 Date:		May 2007
 Contact:	linux-pm@vger.kernel.org
diff --git a/Documentation/power/power_supply_class.txt b/Documentation/power/power_supply_class.txt
index 300d37896e51..7b4be615b4f8 100644
--- a/Documentation/power/power_supply_class.txt
+++ b/Documentation/power/power_supply_class.txt
@@ -137,6 +137,8 @@ power supply object.
 
 INPUT_CURRENT_LIMIT - input current limit programmed by charger. Indicates
 the current drawn from a charging source.
+INPUT_VOLTAGE_LIMIT - input voltage limit programmed by charger. Indicates
+the voltage limit from a charging source.
 
 CHARGE_CONTROL_LIMIT - current charge control limit setting
 CHARGE_CONTROL_LIMIT_MAX - maximum charge control limit setting
diff --git a/drivers/power/supply/power_supply_sysfs.c b/drivers/power/supply/power_supply_sysfs.c
index dce24f596160..5848742ebb59 100644
--- a/drivers/power/supply/power_supply_sysfs.c
+++ b/drivers/power/supply/power_supply_sysfs.c
@@ -275,6 +275,7 @@ static struct device_attribute power_supply_attrs[] = {
 	POWER_SUPPLY_ATTR(charge_control_limit),
 	POWER_SUPPLY_ATTR(charge_control_limit_max),
 	POWER_SUPPLY_ATTR(input_current_limit),
+	POWER_SUPPLY_ATTR(input_voltage_limit),
 	POWER_SUPPLY_ATTR(energy_full_design),
 	POWER_SUPPLY_ATTR(energy_empty_design),
 	POWER_SUPPLY_ATTR(energy_full),
diff --git a/include/linux/power_supply.h b/include/linux/power_supply.h
index 2f9c201a54d1..5cb0d0b5eb19 100644
--- a/include/linux/power_supply.h
+++ b/include/linux/power_supply.h
@@ -122,6 +122,7 @@ enum power_supply_property {
 	POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT,
 	POWER_SUPPLY_PROP_CHARGE_CONTROL_LIMIT_MAX,
 	POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT,
+	POWER_SUPPLY_PROP_INPUT_VOLTAGE_LIMIT,
 	POWER_SUPPLY_PROP_ENERGY_FULL_DESIGN,
 	POWER_SUPPLY_PROP_ENERGY_EMPTY_DESIGN,
 	POWER_SUPPLY_PROP_ENERGY_FULL,
-- 
2.20.1

[RESEND PATCH v3 2/2] power: supply: cros: allow to set input voltage and current limit

[Enric Balletbo i Serra]

This patch allows reading and writing the input voltage and current
limit through the POWER_SUPPLY_PROP_INPUT_VOLTAGE_LIMIT and
POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT sysfs properties. This allows
userspace to see current values and to re-configure these values at
runtime based on system-level knowledge or user input.

By default there is no limit, this is reported as a -1 when reading from
userspace. Writing a value will set the current or voltage limit in uA
or uV, and writing any negative value will remove that limit.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
---

Changes in v3: None
Changes in v2:
- Fix the upper limit that can be set.
- Remove unnecessary else.

 drivers/power/supply/cros_usbpd-charger.c | 116 ++++++++++++++++++++++
 1 file changed, 116 insertions(+)

diff --git a/drivers/power/supply/cros_usbpd-charger.c b/drivers/power/supply/cros_usbpd-charger.c
index 7e9c3984ef6a..3a9ea94c3de3 100644
--- a/drivers/power/supply/cros_usbpd-charger.c
+++ b/drivers/power/supply/cros_usbpd-charger.c
@@ -53,6 +53,8 @@ struct charger_data {
 };
 
 static enum power_supply_property cros_usbpd_charger_props[] = {
+	POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT,
+	POWER_SUPPLY_PROP_INPUT_VOLTAGE_LIMIT,
 	POWER_SUPPLY_PROP_ONLINE,
 	POWER_SUPPLY_PROP_STATUS,
 	POWER_SUPPLY_PROP_CURRENT_MAX,
@@ -80,6 +82,10 @@ static enum power_supply_usb_type cros_usbpd_charger_usb_types[] = {
 	POWER_SUPPLY_USB_TYPE_APPLE_BRICK_ID
 };
 
+/* Input voltage/current limit in mV/mA. Default to none. */
+static u16 input_voltage_limit = EC_POWER_LIMIT_NONE;
+static u16 input_current_limit = EC_POWER_LIMIT_NONE;
+
 static bool cros_usbpd_charger_port_is_dedicated(struct port_data *port)
 {
 	return port->port_number >= port->charger->num_usbpd_ports;
@@ -324,6 +330,26 @@ static int cros_usbpd_charger_get_port_status(struct port_data *port,
 	return ret;
 }
 
+static int cros_usbpd_charger_set_ext_power_limit(struct charger_data *charger,
+						  u16 current_lim,
+						  u16 voltage_lim)
+{
+	struct ec_params_external_power_limit_v1 req;
+	int ret;
+
+	req.current_lim = current_lim;
+	req.voltage_lim = voltage_lim;
+
+	ret = cros_usbpd_charger_ec_command(charger, 0,
+					    EC_CMD_EXTERNAL_POWER_LIMIT,
+					    &req, sizeof(req), NULL, 0);
+	if (ret < 0)
+		dev_err(charger->dev,
+			"Unable to set the 'External Power Limit': %d\n", ret);
+
+	return ret;
+}
+
 static void cros_usbpd_charger_power_changed(struct power_supply *psy)
 {
 	struct port_data *port = power_supply_get_drvdata(psy);
@@ -396,6 +422,18 @@ static int cros_usbpd_charger_get_prop(struct power_supply *psy,
 	case POWER_SUPPLY_PROP_USB_TYPE:
 		val->intval = port->psy_usb_type;
 		break;
+	case POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT:
+		if (input_current_limit == EC_POWER_LIMIT_NONE)
+			val->intval = -1;
+		else
+			val->intval = input_current_limit * 1000;
+		break;
+	case POWER_SUPPLY_PROP_INPUT_VOLTAGE_LIMIT:
+		if (input_voltage_limit == EC_POWER_LIMIT_NONE)
+			val->intval = -1;
+		else
+			val->intval = input_voltage_limit * 1000;
+		break;
 	case POWER_SUPPLY_PROP_MODEL_NAME:
 		val->strval = port->model_name;
 		break;
@@ -409,6 +447,81 @@ static int cros_usbpd_charger_get_prop(struct power_supply *psy,
 	return 0;
 }
 
+static int cros_usbpd_charger_set_prop(struct power_supply *psy,
+				       enum power_supply_property psp,
+				       const union power_supply_propval *val)
+{
+	struct port_data *port = power_supply_get_drvdata(psy);
+	struct charger_data *charger = port->charger;
+	struct device *dev = charger->dev;
+	u16 intval;
+	int ret;
+
+	/* U16_MAX in mV/mA is the maximum supported value */
+	if (val->intval >= U16_MAX * 1000)
+		return -EINVAL;
+	/* A negative number is used to clear the limit */
+	if (val->intval < 0)
+		intval = EC_POWER_LIMIT_NONE;
+	else	/* Convert from uA/uV to mA/mV */
+		intval = val->intval / 1000;
+
+	switch (psp) {
+	case POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT:
+		ret = cros_usbpd_charger_set_ext_power_limit(charger, intval,
+							input_voltage_limit);
+		if (ret < 0)
+			break;
+
+		input_current_limit = intval;
+		if (input_current_limit == EC_POWER_LIMIT_NONE)
+			dev_info(dev,
+			  "External Current Limit cleared for all ports\n");
+		else
+			dev_info(dev,
+			  "External Current Limit set to %dmA for all ports\n",
+			  input_current_limit);
+		break;
+	case POWER_SUPPLY_PROP_INPUT_VOLTAGE_LIMIT:
+		ret = cros_usbpd_charger_set_ext_power_limit(charger,
+							input_current_limit,
+							intval);
+		if (ret < 0)
+			break;
+
+		input_voltage_limit = intval;
+		if (input_voltage_limit == EC_POWER_LIMIT_NONE)
+			dev_info(dev,
+			  "External Voltage Limit cleared for all ports\n");
+		else
+			dev_info(dev,
+			  "External Voltage Limit set to %dmV for all ports\n",
+			  input_voltage_limit);
+		break;
+	default:
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+
+static int cros_usbpd_charger_property_is_writeable(struct power_supply *psy,
+						enum power_supply_property psp)
+{
+	int ret;
+
+	switch (psp) {
+	case POWER_SUPPLY_PROP_INPUT_CURRENT_LIMIT:
+	case POWER_SUPPLY_PROP_INPUT_VOLTAGE_LIMIT:
+		ret = 1;
+		break;
+	default:
+		ret = 0;
+	}
+
+	return ret;
+}
+
 static int cros_usbpd_charger_ec_event(struct notifier_block *nb,
 				       unsigned long queued_during_suspend,
 				       void *_notify)
@@ -525,6 +638,9 @@ static int cros_usbpd_charger_probe(struct platform_device *pd)
 
 		psy_desc = &port->psy_desc;
 		psy_desc->get_property = cros_usbpd_charger_get_prop;
+		psy_desc->set_property = cros_usbpd_charger_set_prop;
+		psy_desc->property_is_writeable =
+				cros_usbpd_charger_property_is_writeable;
 		psy_desc->external_power_changed =
 					cros_usbpd_charger_power_changed;
 		psy_cfg.drv_data = port;
-- 
2.20.1

Re: [RESEND PATCH v3 1/2] power: supply: add input voltage limit property

[Pavel Machek]

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Hi!

> This patch exposes a new property, similar to input current limit, to
> re-configure the maximum voltage from the external supply at runtime
> based on system-level knowledge or user input.

Well, and I suspect it should expose input power limit, not input
voltage limit.

DC-DC convertor efficiency normally does not much depend on input
voltage....

								Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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Re: [RESEND PATCH v3 1/2] power: supply: add input voltage limit property

[Enric Balletbo i Serra]

Hi Pavel,

On 16/4/19 9:19, Pavel Machek wrote:
> Hi!
> 
>> This patch exposes a new property, similar to input current limit, to
>> re-configure the maximum voltage from the external supply at runtime
>> based on system-level knowledge or user input.
> 
> Well, and I suspect it should expose input power limit, not input
> voltage limit.
> 

Oh, ok, I thought we were agree that input voltage had sense after had some
discussion in v3. Seems that no, let me try to give you another example...

> DC-DC convertor efficiency normally does not much depend on input
> voltage....
> 
> 								Pavel
> 

As we said we have a heat "problem" due the internal voltage conversions.

Lets assume you have a linear regulator instead with a Vin range from 5V to 9V
and we want an output of 3.3V/1A

For 9V:
 Input power : P(in) = 9V x 1A = 9W
 Output power: P(out) = 3.3V x 1A = 3.3W
 Regulator power dissipated: P(reg) = P(in) - P(out) = 9W - 3.3W = 5.7W

For 5V:
 Input power : P(in) = 5V x 1A = 5W
 Output power: P(out) = 3.3V x 1A = 3.3W
 Regulator power dissipated: P(reg) = P(in) - P(out) = 5W - 3.3W = 1,7W

In the first case the regulator needs to dissipate more power, hence the
temperature is greater than the second case.

Thanks,
 Enric

Re: [RESEND PATCH v3 1/2] power: supply: add input voltage limit property

[Sebastian Reichel]

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Hi,

On Tue, Apr 16, 2019 at 10:42:30AM +0200, Enric Balletbo i Serra wrote:
> On 16/4/19 9:19, Pavel Machek wrote:
> >> This patch exposes a new property, similar to input current limit, to
> >> re-configure the maximum voltage from the external supply at runtime
> >> based on system-level knowledge or user input.
> > 
> > Well, and I suspect it should expose input power limit, not input
> > voltage limit.
> 
> Oh, ok, I thought we were agree that input voltage had sense after had some
> discussion in v3. Seems that no, let me try to give you another example...
> 
> > DC-DC convertor efficiency normally does not much depend on input
> > voltage....
> 
> As we said we have a heat "problem" due the internal voltage conversions.
> 
> Lets assume you have a linear regulator instead with a Vin range from 5V to 9V
> and we want an output of 3.3V/1A
>
> For 9V:
>  Input power : P(in) = 9V x 1A = 9W
>  Output power: P(out) = 3.3V x 1A = 3.3W
>  Regulator power dissipated: P(reg) = P(in) - P(out) = 9W - 3.3W = 5.7W
> 
> For 5V:
>  Input power : P(in) = 5V x 1A = 5W
>  Output power: P(out) = 3.3V x 1A = 3.3W
>  Regulator power dissipated: P(reg) = P(in) - P(out) = 5W - 3.3W = 1,7W
> 
> In the first case the regulator needs to dissipate more power, hence the
> temperature is greater than the second case.

I would be surprised, if a linear regulator is being used in this
place :) That would basically render functionality of higher voltage
completley useless and a good reason to always limit to 5V. For the
generic case I agree with Pavel, that control over the power (voltage
* current) is the better choice. Still I believe it makes sense to
have a control knob for the voltage available, since some hardware
designs suck.

For example the bad hardware design might be the remote side,
that has issues providing some voltages and this would make it
possible to debug that.

-- Sebastian

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Re: [RESEND PATCH v3 1/2] power: supply: add input voltage limit property

[Pavel Machek]

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Hi!

> On Tue, Apr 16, 2019 at 10:42:30AM +0200, Enric Balletbo i Serra wrote:
> > On 16/4/19 9:19, Pavel Machek wrote:
> > >> This patch exposes a new property, similar to input current limit, to
> > >> re-configure the maximum voltage from the external supply at runtime
> > >> based on system-level knowledge or user input.
> > > 
> > > Well, and I suspect it should expose input power limit, not input
> > > voltage limit.
> > 
> > Oh, ok, I thought we were agree that input voltage had sense after had some
> > discussion in v3. Seems that no, let me try to give you another example...
> > 
> > > DC-DC convertor efficiency normally does not much depend on input
> > > voltage....
> > 
> > As we said we have a heat "problem" due the internal voltage conversions.
> > 
> > Lets assume you have a linear regulator instead with a Vin range from 5V to 9V
> > and we want an output of 3.3V/1A
> >
> > For 9V:
> >  Input power : P(in) = 9V x 1A = 9W
> >  Output power: P(out) = 3.3V x 1A = 3.3W
> >  Regulator power dissipated: P(reg) = P(in) - P(out) = 9W - 3.3W = 5.7W
> > 
> > For 5V:
> >  Input power : P(in) = 5V x 1A = 5W
> >  Output power: P(out) = 3.3V x 1A = 3.3W
> >  Regulator power dissipated: P(reg) = P(in) - P(out) = 5W - 3.3W = 1,7W
> > 
> > In the first case the regulator needs to dissipate more power, hence the
> > temperature is greater than the second case.
> 
> I would be surprised, if a linear regulator is being used in this
> place :) That would basically render functionality of higher voltage
> completley useless and a good reason to always limit to 5V. For the
> generic case I agree with Pavel, that control over the power (voltage
> * current) is the better choice. Still I believe it makes sense to
> have a control knob for the voltage available, since some hardware
> designs suck.
> 
> For example the bad hardware design might be the remote side,
> that has issues providing some voltages and this would make it
> possible to debug that.

Ok, I agree it might be useful _somewhere_, mostly for hardware
debugging. But before if we add voltage_limit, lets add power_limit,
too; and for problems that can be solved using power_limit, lets use
power_limit...

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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