[PATCHv1,1/2] power: supply: gpio-charger: add charge-current-limit feature
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Message ID 20200513115601.360642-1-sebastian.reichel@collabora.com
State New
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  • [PATCHv1,1/2] power: supply: gpio-charger: add charge-current-limit feature
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Commit Message

Sebastian Reichel May 13, 2020, 11:56 a.m. UTC
Add new charge-current-limit feature to gpio-charger. This also
makes the online status GPIO optional, since hardware might only
expose the charge-current-limit feature and there is no good reason
to have it mandatory now that different GPIOs are supported.

Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
---
 .../bindings/power/supply/gpio-charger.txt    |  11 +-
 drivers/power/supply/gpio-charger.c           | 176 ++++++++++++++++--
 2 files changed, 174 insertions(+), 13 deletions(-)

Comments

Emil Velikov May 15, 2020, 1:24 p.m. UTC | #1
Hi Sebastian,

I've left a few trivial suggestions, although I suspect only one of them
really matters. Namely - I think as-is the code changes the legacy behaviour
when OF is missing.

Mind you, this is my third time skimming through power/supply, so take it with
a grain of salt.

On 2020/05/13, Sebastian Reichel wrote:
> Add new charge-current-limit feature to gpio-charger. This also
> makes the online status GPIO optional, since hardware might only
> expose the charge-current-limit feature and there is no good reason
> to have it mandatory now that different GPIOs are supported.
> 
> Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
> ---
>  .../bindings/power/supply/gpio-charger.txt    |  11 +-
>  drivers/power/supply/gpio-charger.c           | 176 ++++++++++++++++--
>  2 files changed, 174 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/power/supply/gpio-charger.txt b/Documentation/devicetree/bindings/power/supply/gpio-charger.txt
> index 0fb33b2c62a6..dbfd29029f69 100644
> --- a/Documentation/devicetree/bindings/power/supply/gpio-charger.txt
> +++ b/Documentation/devicetree/bindings/power/supply/gpio-charger.txt
> @@ -2,8 +2,6 @@ gpio-charger
>  
>  Required properties :
>   - compatible : "gpio-charger"
> - - gpios : GPIO indicating the charger presence.
> -   See GPIO binding in bindings/gpio/gpio.txt .
>   - charger-type : power supply type, one of
>       unknown
>       battery
> @@ -15,7 +13,13 @@ Required properties :
>       usb-aca (USB accessory charger adapter)
>  
>  Optional properties:
> + - gpios : GPIO indicating the charger presence.
> +   See GPIO binding in bindings/gpio/gpio.txt .
>   - charge-status-gpios: GPIO indicating whether a battery is charging.
> + - charge-current-limit-gpios: Output GPIOs specifiers for limiting the charge current
> + - charge-current-limit-mapping: List of touples with current in uA and a GPIO bitmap (in this order).
> +                                The GPIOs are encoded in the same order as specified in charge-current-limit-gpios.
> +				The touples must be provided in descending order of the current limit.

Minor tweaks:

	List of tuples with current in uA and a GPIO bitmap.
	Tuples must be sorted in descending order of the current limit.
	GPIOs are encoded in the order as specified in charge-current-limit-gpios.


> +static int init_charge_current_limit(struct device *dev,
> +				    struct gpio_charger *gpio_charger)
> +{
> +	int i, len;
> +	u32 cur_limit = U32_MAX;
> +
> +	gpio_charger->current_limit_gpios = devm_gpiod_get_array_optional(dev,
> +		"charge-current-limit", GPIOD_OUT_LOW);
> +	if (IS_ERR(gpio_charger->current_limit_gpios)) {
> +		dev_err(dev, "error getting current-limit GPIOs\n");
> +		return PTR_ERR(gpio_charger->current_limit_gpios);
> +	}
> +
> +	if (!gpio_charger->current_limit_gpios)
> +		return 0;
> +
> +	len = device_property_read_u32_array(dev, "charge-current-limit-mapping",
> +		NULL, 0);
> +	if (len < 0)

The properly is optional, although I'm not sure if having an 'empty' properly
(len == 0) should be considered an error as indicated by -ENOMEM below or not.

Worth documenting that, unless it's covered already.

> +		return len;
> +
> +	if (len % 2) {
> +		dev_err(dev, "invalid charge-current-limit-mapping length\n");
> +		return -EINVAL;
> +	}
> +
> +	gpio_charger->current_limit_map = devm_kmalloc_array(dev,
> +		len / 2, sizeof(*gpio_charger->current_limit_map), GFP_KERNEL);
> +	if (!gpio_charger->current_limit_map)
> +		return -ENOMEM;
> +
> +	gpio_charger->current_limit_map_size = len / 2;
> +
> +	len = device_property_read_u32_array(dev, "charge-current-limit-mapping",
> +		(u32*) gpio_charger->current_limit_map, len);
> +	if (len < 0)
> +		return len;
> +
> +	for (i=0; i < gpio_charger->current_limit_map_size; i++) {
> +		if (gpio_charger->current_limit_map[i].limit_ua > cur_limit) {
> +			dev_err(dev, "invalid charge-current-limit-mapping\n");
Would make sense to use something more descriptive than "invalid". Say "not
sorted by current descending order"?


> @@ -137,18 +270,19 @@ static int gpio_charger_probe(struct platform_device *pdev)

>  	/*
>  	 * If this fails and we're not using device tree, try the
>  	 * legacy platform data method.
>  	 */
> -	if (IS_ERR(gpio_charger->gpiod) && !dev->of_node) {
> +	if (!gpio_charger->gpiod && !dev->of_node) {
The original code will attempt the legacy code for ... (from the doc)

 * ..., -ENOENT if no GPIO has been assigned to the requested function, or
 * another IS_ERR() code if an error occurred while trying to acquire the GPIO.

While the new code will only consider -ENOENT.

Using IS_ERR_OR_NULL(gpio_charger->gpiod) should preserve the original
behaviour.


>  		/* Non-DT: use legacy GPIO numbers */
>  		if (!gpio_is_valid(pdata->gpio)) {
>  			dev_err(dev, "Invalid gpio pin in pdata\n");
> @@ -173,18 +307,38 @@ static int gpio_charger_probe(struct platform_device *pdev)
>  		return PTR_ERR(gpio_charger->gpiod);
>  	}
>  
> +	if (gpio_charger->gpiod &&
> +	    num_props < ARRAY_SIZE(gpio_charger_properties)) {
> +		gpio_charger_properties[num_props] = POWER_SUPPLY_PROP_ONLINE;
The ARRAY_SIZE() check here (and below) are always true, albeit not dead code.

IMHO the beefy comment above gpio_charger_properties, plus review process is
enough to catch these issues, so it can be dropped.


>  	charger_desc = &gpio_charger->charger_desc;
>  	charger_desc->properties = gpio_charger_properties;

Aside: any particular reason why power_supply_desc::properties isn't const?

-Emil
Rob Herring May 28, 2020, 1:56 a.m. UTC | #2
On Wed, May 13, 2020 at 01:56:00PM +0200, Sebastian Reichel wrote:
> Add new charge-current-limit feature to gpio-charger. This also
> makes the online status GPIO optional, since hardware might only
> expose the charge-current-limit feature and there is no good reason
> to have it mandatory now that different GPIOs are supported.
> 
> Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>
> ---
>  .../bindings/power/supply/gpio-charger.txt    |  11 +-
>  drivers/power/supply/gpio-charger.c           | 176 ++++++++++++++++--
>  2 files changed, 174 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/power/supply/gpio-charger.txt b/Documentation/devicetree/bindings/power/supply/gpio-charger.txt
> index 0fb33b2c62a6..dbfd29029f69 100644
> --- a/Documentation/devicetree/bindings/power/supply/gpio-charger.txt
> +++ b/Documentation/devicetree/bindings/power/supply/gpio-charger.txt
> @@ -2,8 +2,6 @@ gpio-charger
>  
>  Required properties :
>   - compatible : "gpio-charger"
> - - gpios : GPIO indicating the charger presence.
> -   See GPIO binding in bindings/gpio/gpio.txt .
>   - charger-type : power supply type, one of
>       unknown
>       battery
> @@ -15,7 +13,13 @@ Required properties :
>       usb-aca (USB accessory charger adapter)
>  
>  Optional properties:
> + - gpios : GPIO indicating the charger presence.
> +   See GPIO binding in bindings/gpio/gpio.txt .
>   - charge-status-gpios: GPIO indicating whether a battery is charging.
> + - charge-current-limit-gpios: Output GPIOs specifiers for limiting the charge current
> + - charge-current-limit-mapping: List of touples with current in uA and a GPIO bitmap (in this order).
> +                                The GPIOs are encoded in the same order as specified in charge-current-limit-gpios.

TBC, index 0 GPIO is bit 0?

> +				The touples must be provided in descending order of the current limit.

tuples

Wrap at 80 columns.

>  
>  Example:
>  
> @@ -24,6 +28,9 @@ Example:
>  		charger-type = "usb-sdp";
>  		gpios = <&gpd 28 GPIO_ACTIVE_LOW>;
>  		charge-status-gpios = <&gpc 27 GPIO_ACTIVE_LOW>;
> +
> +		charge-current-limit-gpios = <&gpioA 11 GPIO_ACTIVE_HIGH>, <&gpioA 12 GPIO_ACTIVE_HIGH>;
> +		charge-current-limit-mapping = <2500000 0x00>, <700000 0x01>, <0 0x02>;
>  	};
>  
>  	battery {
> diff --git a/drivers/power/supply/gpio-charger.c b/drivers/power/supply/gpio-charger.c
> index 1b959c7f8b0e..4a5eac7cc36c 100644
> --- a/drivers/power/supply/gpio-charger.c
> +++ b/drivers/power/supply/gpio-charger.c
> @@ -18,7 +18,13 @@
>  
>  #include <linux/power/gpio-charger.h>
>  
> +struct gpio_mapping {
> +	u32 limit_ua;
> +	u32 gpiodata;
> +} __packed;
> +
>  struct gpio_charger {
> +	struct device *dev;
>  	unsigned int irq;
>  	unsigned int charge_status_irq;
>  	bool wakeup_enabled;
> @@ -27,6 +33,11 @@ struct gpio_charger {
>  	struct power_supply_desc charger_desc;
>  	struct gpio_desc *gpiod;
>  	struct gpio_desc *charge_status;
> +
> +	struct gpio_descs *current_limit_gpios;
> +	struct gpio_mapping *current_limit_map;
> +	u32 current_limit_map_size;
> +	u32 charge_current_limit;
>  };
>  
>  static irqreturn_t gpio_charger_irq(int irq, void *devid)
> @@ -43,6 +54,35 @@ static inline struct gpio_charger *psy_to_gpio_charger(struct power_supply *psy)
>  	return power_supply_get_drvdata(psy);
>  }
>  
> +static int set_charge_current_limit(struct gpio_charger *gpio_charger, int val)
> +{
> +	struct gpio_mapping mapping;
> +	int ndescs = gpio_charger->current_limit_gpios->ndescs;
> +	struct gpio_desc **gpios = gpio_charger->current_limit_gpios->desc;
> +	int i;
> +
> +	if (!gpio_charger->current_limit_map_size)
> +		return -EINVAL;
> +
> +	for (i = 0; i < gpio_charger->current_limit_map_size; i++) {
> +		if (gpio_charger->current_limit_map[i].limit_ua <= val)
> +			break;
> +	}
> +	mapping = gpio_charger->current_limit_map[i];
> +
> +	for (i = 0; i < ndescs; i++) {
> +		bool val = (mapping.gpiodata >> i) & 1;
> +		gpiod_set_value_cansleep(gpios[ndescs-i-1], val);
> +	}
> +
> +	gpio_charger->charge_current_limit = mapping.limit_ua;
> +
> +	dev_dbg(gpio_charger->dev, "set charge current limit to %d (requested: %d)\n",
> +		gpio_charger->charge_current_limit, val);
> +
> +	return 0;
> +}
> +
>  static int gpio_charger_get_property(struct power_supply *psy,
>  		enum power_supply_property psp, union power_supply_propval *val)
>  {
> @@ -58,6 +98,9 @@ static int gpio_charger_get_property(struct power_supply *psy,
>  		else
>  			val->intval = POWER_SUPPLY_STATUS_NOT_CHARGING;
>  		break;
> +	case POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX:
> +		val->intval = gpio_charger->charge_current_limit;
> +		break;
>  	default:
>  		return -EINVAL;
>  	}
> @@ -65,6 +108,34 @@ static int gpio_charger_get_property(struct power_supply *psy,
>  	return 0;
>  }
>  
> +static int gpio_charger_set_property(struct power_supply *psy,
> +	enum power_supply_property psp, const union power_supply_propval *val)
> +{
> +	struct gpio_charger *gpio_charger = psy_to_gpio_charger(psy);
> +
> +	switch (psp) {
> +	case POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX:
> +		return set_charge_current_limit(gpio_charger, val->intval);
> +	default:
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +static int gpio_charger_property_is_writeable(struct power_supply *psy,
> +					      enum power_supply_property psp)
> +{
> +	switch (psp) {
> +	case POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX:
> +		return 1;
> +	default:
> +		break;
> +	}
> +
> +	return 0;
> +}
> +
>  static enum power_supply_type gpio_charger_get_type(struct device *dev)
>  {
>  	const char *chargetype;
> @@ -112,9 +183,70 @@ static int gpio_charger_get_irq(struct device *dev, void *dev_id,
>  	return irq;
>  }
>  
> +static int init_charge_current_limit(struct device *dev,
> +				    struct gpio_charger *gpio_charger)
> +{
> +	int i, len;
> +	u32 cur_limit = U32_MAX;
> +
> +	gpio_charger->current_limit_gpios = devm_gpiod_get_array_optional(dev,
> +		"charge-current-limit", GPIOD_OUT_LOW);
> +	if (IS_ERR(gpio_charger->current_limit_gpios)) {
> +		dev_err(dev, "error getting current-limit GPIOs\n");
> +		return PTR_ERR(gpio_charger->current_limit_gpios);
> +	}
> +
> +	if (!gpio_charger->current_limit_gpios)
> +		return 0;
> +
> +	len = device_property_read_u32_array(dev, "charge-current-limit-mapping",
> +		NULL, 0);
> +	if (len < 0)
> +		return len;
> +
> +	if (len % 2) {
> +		dev_err(dev, "invalid charge-current-limit-mapping length\n");
> +		return -EINVAL;
> +	}
> +
> +	gpio_charger->current_limit_map = devm_kmalloc_array(dev,
> +		len / 2, sizeof(*gpio_charger->current_limit_map), GFP_KERNEL);
> +	if (!gpio_charger->current_limit_map)
> +		return -ENOMEM;
> +
> +	gpio_charger->current_limit_map_size = len / 2;
> +
> +	len = device_property_read_u32_array(dev, "charge-current-limit-mapping",
> +		(u32*) gpio_charger->current_limit_map, len);
> +	if (len < 0)
> +		return len;
> +
> +	for (i=0; i < gpio_charger->current_limit_map_size; i++) {
> +		if (gpio_charger->current_limit_map[i].limit_ua > cur_limit) {
> +			dev_err(dev, "invalid charge-current-limit-mapping\n");
> +			return -EINVAL;
> +		}
> +
> +		cur_limit = gpio_charger->current_limit_map[i].limit_ua;
> +	}
> +
> +	/* default to smallest current limitation for safety reasons */
> +	len = gpio_charger->current_limit_map_size - 1;
> +	set_charge_current_limit(gpio_charger,
> +		gpio_charger->current_limit_map[len].limit_ua);
> +
> +	return 0;
> +}
> +
> +/*
> + * The entries will be overwritten by driver's probe routine depending
> + * on the available features. This list ensures, that the array is big
> + * enough for all optional features.
> + */
>  static enum power_supply_property gpio_charger_properties[] = {
>  	POWER_SUPPLY_PROP_ONLINE,
> -	POWER_SUPPLY_PROP_STATUS /* Must always be last in the array. */
> +	POWER_SUPPLY_PROP_STATUS,
> +	POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX,
>  };
>  
>  static int gpio_charger_probe(struct platform_device *pdev)
> @@ -128,6 +260,7 @@ static int gpio_charger_probe(struct platform_device *pdev)
>  	int charge_status_irq;
>  	unsigned long flags;
>  	int ret;
> +	int num_props = 0;
>  
>  	if (!pdata && !dev->of_node) {
>  		dev_err(dev, "No platform data\n");
> @@ -137,18 +270,19 @@ static int gpio_charger_probe(struct platform_device *pdev)
>  	gpio_charger = devm_kzalloc(dev, sizeof(*gpio_charger), GFP_KERNEL);
>  	if (!gpio_charger)
>  		return -ENOMEM;
> +	gpio_charger->dev = dev;
>  
>  	/*
>  	 * This will fetch a GPIO descriptor from device tree, ACPI or
>  	 * boardfile descriptor tables. It's good to try this first.
>  	 */
> -	gpio_charger->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN);
> +	gpio_charger->gpiod = devm_gpiod_get_optional(dev, NULL, GPIOD_IN);
>  
>  	/*
>  	 * If this fails and we're not using device tree, try the
>  	 * legacy platform data method.
>  	 */
> -	if (IS_ERR(gpio_charger->gpiod) && !dev->of_node) {
> +	if (!gpio_charger->gpiod && !dev->of_node) {
>  		/* Non-DT: use legacy GPIO numbers */
>  		if (!gpio_is_valid(pdata->gpio)) {
>  			dev_err(dev, "Invalid gpio pin in pdata\n");
> @@ -173,18 +307,38 @@ static int gpio_charger_probe(struct platform_device *pdev)
>  		return PTR_ERR(gpio_charger->gpiod);
>  	}
>  
> +	if (gpio_charger->gpiod &&
> +	    num_props < ARRAY_SIZE(gpio_charger_properties)) {
> +		gpio_charger_properties[num_props] = POWER_SUPPLY_PROP_ONLINE;
> +		num_props++;
> +	}
> +
>  	charge_status = devm_gpiod_get_optional(dev, "charge-status", GPIOD_IN);
> -	gpio_charger->charge_status = charge_status;
> -	if (IS_ERR(gpio_charger->charge_status))
> -		return PTR_ERR(gpio_charger->charge_status);
> +	if (IS_ERR(charge_status))
> +		return PTR_ERR(charge_status);
> +	if (charge_status && num_props < ARRAY_SIZE(gpio_charger_properties)) {
> +		gpio_charger->charge_status = charge_status;
> +		gpio_charger_properties[num_props] = POWER_SUPPLY_PROP_STATUS;
> +		num_props++;
> +	}
> +
> +	ret = init_charge_current_limit(dev, gpio_charger);
> +	if (ret < 0)
> +		return ret;
> +	if (gpio_charger->current_limit_map &&
> +	    num_props < ARRAY_SIZE(gpio_charger_properties)) {
> +		gpio_charger_properties[num_props] =
> +			POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX;
> +		num_props++;
> +	}
>  
>  	charger_desc = &gpio_charger->charger_desc;
>  	charger_desc->properties = gpio_charger_properties;
> -	charger_desc->num_properties = ARRAY_SIZE(gpio_charger_properties);
> -	/* Remove POWER_SUPPLY_PROP_STATUS from the supported properties. */
> -	if (!gpio_charger->charge_status)
> -		charger_desc->num_properties -= 1;
> +	charger_desc->num_properties = num_props;
>  	charger_desc->get_property = gpio_charger_get_property;
> +	charger_desc->set_property = gpio_charger_set_property;
> +	charger_desc->property_is_writeable =
> +					gpio_charger_property_is_writeable;
>  
>  	psy_cfg.of_node = dev->of_node;
>  	psy_cfg.drv_data = gpio_charger;
> @@ -269,6 +423,6 @@ static struct platform_driver gpio_charger_driver = {
>  module_platform_driver(gpio_charger_driver);
>  
>  MODULE_AUTHOR("Lars-Peter Clausen <lars@metafoo.de>");
> -MODULE_DESCRIPTION("Driver for chargers which report their online status through a GPIO");
> +MODULE_DESCRIPTION("Driver for chargers only communicating via GPIO(s)");
>  MODULE_LICENSE("GPL");
>  MODULE_ALIAS("platform:gpio-charger");
> -- 
> 2.26.2
>

Patch
diff mbox series

diff --git a/Documentation/devicetree/bindings/power/supply/gpio-charger.txt b/Documentation/devicetree/bindings/power/supply/gpio-charger.txt
index 0fb33b2c62a6..dbfd29029f69 100644
--- a/Documentation/devicetree/bindings/power/supply/gpio-charger.txt
+++ b/Documentation/devicetree/bindings/power/supply/gpio-charger.txt
@@ -2,8 +2,6 @@  gpio-charger
 
 Required properties :
  - compatible : "gpio-charger"
- - gpios : GPIO indicating the charger presence.
-   See GPIO binding in bindings/gpio/gpio.txt .
  - charger-type : power supply type, one of
      unknown
      battery
@@ -15,7 +13,13 @@  Required properties :
      usb-aca (USB accessory charger adapter)
 
 Optional properties:
+ - gpios : GPIO indicating the charger presence.
+   See GPIO binding in bindings/gpio/gpio.txt .
  - charge-status-gpios: GPIO indicating whether a battery is charging.
+ - charge-current-limit-gpios: Output GPIOs specifiers for limiting the charge current
+ - charge-current-limit-mapping: List of touples with current in uA and a GPIO bitmap (in this order).
+                                The GPIOs are encoded in the same order as specified in charge-current-limit-gpios.
+				The touples must be provided in descending order of the current limit.
 
 Example:
 
@@ -24,6 +28,9 @@  Example:
 		charger-type = "usb-sdp";
 		gpios = <&gpd 28 GPIO_ACTIVE_LOW>;
 		charge-status-gpios = <&gpc 27 GPIO_ACTIVE_LOW>;
+
+		charge-current-limit-gpios = <&gpioA 11 GPIO_ACTIVE_HIGH>, <&gpioA 12 GPIO_ACTIVE_HIGH>;
+		charge-current-limit-mapping = <2500000 0x00>, <700000 0x01>, <0 0x02>;
 	};
 
 	battery {
diff --git a/drivers/power/supply/gpio-charger.c b/drivers/power/supply/gpio-charger.c
index 1b959c7f8b0e..4a5eac7cc36c 100644
--- a/drivers/power/supply/gpio-charger.c
+++ b/drivers/power/supply/gpio-charger.c
@@ -18,7 +18,13 @@ 
 
 #include <linux/power/gpio-charger.h>
 
+struct gpio_mapping {
+	u32 limit_ua;
+	u32 gpiodata;
+} __packed;
+
 struct gpio_charger {
+	struct device *dev;
 	unsigned int irq;
 	unsigned int charge_status_irq;
 	bool wakeup_enabled;
@@ -27,6 +33,11 @@  struct gpio_charger {
 	struct power_supply_desc charger_desc;
 	struct gpio_desc *gpiod;
 	struct gpio_desc *charge_status;
+
+	struct gpio_descs *current_limit_gpios;
+	struct gpio_mapping *current_limit_map;
+	u32 current_limit_map_size;
+	u32 charge_current_limit;
 };
 
 static irqreturn_t gpio_charger_irq(int irq, void *devid)
@@ -43,6 +54,35 @@  static inline struct gpio_charger *psy_to_gpio_charger(struct power_supply *psy)
 	return power_supply_get_drvdata(psy);
 }
 
+static int set_charge_current_limit(struct gpio_charger *gpio_charger, int val)
+{
+	struct gpio_mapping mapping;
+	int ndescs = gpio_charger->current_limit_gpios->ndescs;
+	struct gpio_desc **gpios = gpio_charger->current_limit_gpios->desc;
+	int i;
+
+	if (!gpio_charger->current_limit_map_size)
+		return -EINVAL;
+
+	for (i = 0; i < gpio_charger->current_limit_map_size; i++) {
+		if (gpio_charger->current_limit_map[i].limit_ua <= val)
+			break;
+	}
+	mapping = gpio_charger->current_limit_map[i];
+
+	for (i = 0; i < ndescs; i++) {
+		bool val = (mapping.gpiodata >> i) & 1;
+		gpiod_set_value_cansleep(gpios[ndescs-i-1], val);
+	}
+
+	gpio_charger->charge_current_limit = mapping.limit_ua;
+
+	dev_dbg(gpio_charger->dev, "set charge current limit to %d (requested: %d)\n",
+		gpio_charger->charge_current_limit, val);
+
+	return 0;
+}
+
 static int gpio_charger_get_property(struct power_supply *psy,
 		enum power_supply_property psp, union power_supply_propval *val)
 {
@@ -58,6 +98,9 @@  static int gpio_charger_get_property(struct power_supply *psy,
 		else
 			val->intval = POWER_SUPPLY_STATUS_NOT_CHARGING;
 		break;
+	case POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX:
+		val->intval = gpio_charger->charge_current_limit;
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -65,6 +108,34 @@  static int gpio_charger_get_property(struct power_supply *psy,
 	return 0;
 }
 
+static int gpio_charger_set_property(struct power_supply *psy,
+	enum power_supply_property psp, const union power_supply_propval *val)
+{
+	struct gpio_charger *gpio_charger = psy_to_gpio_charger(psy);
+
+	switch (psp) {
+	case POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX:
+		return set_charge_current_limit(gpio_charger, val->intval);
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int gpio_charger_property_is_writeable(struct power_supply *psy,
+					      enum power_supply_property psp)
+{
+	switch (psp) {
+	case POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX:
+		return 1;
+	default:
+		break;
+	}
+
+	return 0;
+}
+
 static enum power_supply_type gpio_charger_get_type(struct device *dev)
 {
 	const char *chargetype;
@@ -112,9 +183,70 @@  static int gpio_charger_get_irq(struct device *dev, void *dev_id,
 	return irq;
 }
 
+static int init_charge_current_limit(struct device *dev,
+				    struct gpio_charger *gpio_charger)
+{
+	int i, len;
+	u32 cur_limit = U32_MAX;
+
+	gpio_charger->current_limit_gpios = devm_gpiod_get_array_optional(dev,
+		"charge-current-limit", GPIOD_OUT_LOW);
+	if (IS_ERR(gpio_charger->current_limit_gpios)) {
+		dev_err(dev, "error getting current-limit GPIOs\n");
+		return PTR_ERR(gpio_charger->current_limit_gpios);
+	}
+
+	if (!gpio_charger->current_limit_gpios)
+		return 0;
+
+	len = device_property_read_u32_array(dev, "charge-current-limit-mapping",
+		NULL, 0);
+	if (len < 0)
+		return len;
+
+	if (len % 2) {
+		dev_err(dev, "invalid charge-current-limit-mapping length\n");
+		return -EINVAL;
+	}
+
+	gpio_charger->current_limit_map = devm_kmalloc_array(dev,
+		len / 2, sizeof(*gpio_charger->current_limit_map), GFP_KERNEL);
+	if (!gpio_charger->current_limit_map)
+		return -ENOMEM;
+
+	gpio_charger->current_limit_map_size = len / 2;
+
+	len = device_property_read_u32_array(dev, "charge-current-limit-mapping",
+		(u32*) gpio_charger->current_limit_map, len);
+	if (len < 0)
+		return len;
+
+	for (i=0; i < gpio_charger->current_limit_map_size; i++) {
+		if (gpio_charger->current_limit_map[i].limit_ua > cur_limit) {
+			dev_err(dev, "invalid charge-current-limit-mapping\n");
+			return -EINVAL;
+		}
+
+		cur_limit = gpio_charger->current_limit_map[i].limit_ua;
+	}
+
+	/* default to smallest current limitation for safety reasons */
+	len = gpio_charger->current_limit_map_size - 1;
+	set_charge_current_limit(gpio_charger,
+		gpio_charger->current_limit_map[len].limit_ua);
+
+	return 0;
+}
+
+/*
+ * The entries will be overwritten by driver's probe routine depending
+ * on the available features. This list ensures, that the array is big
+ * enough for all optional features.
+ */
 static enum power_supply_property gpio_charger_properties[] = {
 	POWER_SUPPLY_PROP_ONLINE,
-	POWER_SUPPLY_PROP_STATUS /* Must always be last in the array. */
+	POWER_SUPPLY_PROP_STATUS,
+	POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX,
 };
 
 static int gpio_charger_probe(struct platform_device *pdev)
@@ -128,6 +260,7 @@  static int gpio_charger_probe(struct platform_device *pdev)
 	int charge_status_irq;
 	unsigned long flags;
 	int ret;
+	int num_props = 0;
 
 	if (!pdata && !dev->of_node) {
 		dev_err(dev, "No platform data\n");
@@ -137,18 +270,19 @@  static int gpio_charger_probe(struct platform_device *pdev)
 	gpio_charger = devm_kzalloc(dev, sizeof(*gpio_charger), GFP_KERNEL);
 	if (!gpio_charger)
 		return -ENOMEM;
+	gpio_charger->dev = dev;
 
 	/*
 	 * This will fetch a GPIO descriptor from device tree, ACPI or
 	 * boardfile descriptor tables. It's good to try this first.
 	 */
-	gpio_charger->gpiod = devm_gpiod_get(dev, NULL, GPIOD_IN);
+	gpio_charger->gpiod = devm_gpiod_get_optional(dev, NULL, GPIOD_IN);
 
 	/*
 	 * If this fails and we're not using device tree, try the
 	 * legacy platform data method.
 	 */
-	if (IS_ERR(gpio_charger->gpiod) && !dev->of_node) {
+	if (!gpio_charger->gpiod && !dev->of_node) {
 		/* Non-DT: use legacy GPIO numbers */
 		if (!gpio_is_valid(pdata->gpio)) {
 			dev_err(dev, "Invalid gpio pin in pdata\n");
@@ -173,18 +307,38 @@  static int gpio_charger_probe(struct platform_device *pdev)
 		return PTR_ERR(gpio_charger->gpiod);
 	}
 
+	if (gpio_charger->gpiod &&
+	    num_props < ARRAY_SIZE(gpio_charger_properties)) {
+		gpio_charger_properties[num_props] = POWER_SUPPLY_PROP_ONLINE;
+		num_props++;
+	}
+
 	charge_status = devm_gpiod_get_optional(dev, "charge-status", GPIOD_IN);
-	gpio_charger->charge_status = charge_status;
-	if (IS_ERR(gpio_charger->charge_status))
-		return PTR_ERR(gpio_charger->charge_status);
+	if (IS_ERR(charge_status))
+		return PTR_ERR(charge_status);
+	if (charge_status && num_props < ARRAY_SIZE(gpio_charger_properties)) {
+		gpio_charger->charge_status = charge_status;
+		gpio_charger_properties[num_props] = POWER_SUPPLY_PROP_STATUS;
+		num_props++;
+	}
+
+	ret = init_charge_current_limit(dev, gpio_charger);
+	if (ret < 0)
+		return ret;
+	if (gpio_charger->current_limit_map &&
+	    num_props < ARRAY_SIZE(gpio_charger_properties)) {
+		gpio_charger_properties[num_props] =
+			POWER_SUPPLY_PROP_CONSTANT_CHARGE_CURRENT_MAX;
+		num_props++;
+	}
 
 	charger_desc = &gpio_charger->charger_desc;
 	charger_desc->properties = gpio_charger_properties;
-	charger_desc->num_properties = ARRAY_SIZE(gpio_charger_properties);
-	/* Remove POWER_SUPPLY_PROP_STATUS from the supported properties. */
-	if (!gpio_charger->charge_status)
-		charger_desc->num_properties -= 1;
+	charger_desc->num_properties = num_props;
 	charger_desc->get_property = gpio_charger_get_property;
+	charger_desc->set_property = gpio_charger_set_property;
+	charger_desc->property_is_writeable =
+					gpio_charger_property_is_writeable;
 
 	psy_cfg.of_node = dev->of_node;
 	psy_cfg.drv_data = gpio_charger;
@@ -269,6 +423,6 @@  static struct platform_driver gpio_charger_driver = {
 module_platform_driver(gpio_charger_driver);
 
 MODULE_AUTHOR("Lars-Peter Clausen <lars@metafoo.de>");
-MODULE_DESCRIPTION("Driver for chargers which report their online status through a GPIO");
+MODULE_DESCRIPTION("Driver for chargers only communicating via GPIO(s)");
 MODULE_LICENSE("GPL");
 MODULE_ALIAS("platform:gpio-charger");