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Subject[PATCH v2] leds: pwm: add support for default-state device property
Date
This patch adds support for "default-state" devicetree property, which
allows to defer pwm init to first use of led.

This allows to configure the PWM early in bootloader to let the LED
blink until an application in Linux userspace set something different.

Signed-off-by: Denis Osterland-Heim <Denis.Osterland@diehl.com>
---
v1->v2:
- use default-state = "keep", as suggested by Jacek Anaszewski
- calc initial brightness with PWM state from device

.../devicetree/bindings/leds/leds-pwm.txt | 2 ++
drivers/leds/leds-pwm.c | 33 +++++++++++++++++--
include/linux/leds_pwm.h | 1 +
3 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/leds/leds-pwm.txt b/Documentation/devicetree/bindings/leds/leds-pwm.txt
index 6c6583c35f2f..d0f489680594 100644
--- a/Documentation/devicetree/bindings/leds/leds-pwm.txt
+++ b/Documentation/devicetree/bindings/leds/leds-pwm.txt
@@ -19,6 +19,8 @@ LED sub-node properties:
see Documentation/devicetree/bindings/leds/common.txt
- linux,default-trigger : (optional)
see Documentation/devicetree/bindings/leds/common.txt
+- default-state : (optional)
+ see Documentation/devicetree/bindings/leds/common.yaml

Example:

diff --git a/drivers/leds/leds-pwm.c b/drivers/leds/leds-pwm.c
index 8b6965a563e9..92726c2e43ba 100644
--- a/drivers/leds/leds-pwm.c
+++ b/drivers/leds/leds-pwm.c
@@ -75,7 +75,8 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
led_data->active_low = led->active_low;
led_data->cdev.name = led->name;
led_data->cdev.default_trigger = led->default_trigger;
- led_data->cdev.brightness = LED_OFF;
+ ret = led->default_state == LEDS_GPIO_DEFSTATE_ON;
+ led_data->cdev.brightness = ret ? led->max_brightness : LED_OFF;
led_data->cdev.max_brightness = led->max_brightness;
led_data->cdev.flags = LED_CORE_SUSPENDRESUME;

@@ -97,7 +98,8 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
* FIXME: pwm_apply_args() should be removed when switching to the
* atomic PWM API.
*/
- pwm_apply_args(led_data->pwm);
+ if (led->default_state != LEDS_GPIO_DEFSTATE_KEEP)
+ pwm_apply_args(led_data->pwm);

pwm_get_args(led_data->pwm, &pargs);

@@ -105,10 +107,23 @@ static int led_pwm_add(struct device *dev, struct led_pwm_priv *priv,
if (!led_data->period && (led->pwm_period_ns > 0))
led_data->period = led->pwm_period_ns;

+ if (led->default_state == LEDS_GPIO_DEFSTATE_KEEP) {
+ uint64_t brightness;
+ struct pwm_device *pwm = led_data->pwm;
+ struct pwm_state state;
+
+ pwm->chip->ops->get_state(pwm->chip, pwm, &state);
+ brightness = led->max_brightness * state.duty_cycle;
+ do_div(brightness, state.period);
+ led_data->cdev.brightness = (enum led_brightness)brightness;
+ }
+
ret = devm_led_classdev_register(dev, &led_data->cdev);
if (ret == 0) {
priv->num_leds++;
- led_pwm_set(&led_data->cdev, led_data->cdev.brightness);
+ if (led->default_state != LEDS_GPIO_DEFSTATE_KEEP)
+ led_pwm_set(&led_data->cdev,
+ led_data->cdev.brightness);
} else {
dev_err(dev, "failed to register PWM led for %s: %d\n",
led->name, ret);
@@ -126,6 +141,8 @@ static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv)
memset(&led, 0, sizeof(led));

device_for_each_child_node(dev, fwnode) {
+ const char *state = NULL;
+
ret = fwnode_property_read_string(fwnode, "label", &led.name);
if (ret && is_of_node(fwnode))
led.name = to_of_node(fwnode)->name;
@@ -143,6 +160,16 @@ static int led_pwm_create_fwnode(struct device *dev, struct led_pwm_priv *priv)
fwnode_property_read_u32(fwnode, "max-brightness",
&led.max_brightness);

+ if (!fwnode_property_read_string(fwnode, "default-state",
+ &state)) {
+ if (!strcmp(state, "keep"))
+ led.default_state = LEDS_GPIO_DEFSTATE_KEEP;
+ else if (!strcmp(state, "on"))
+ led.default_state = LEDS_GPIO_DEFSTATE_ON;
+ else
+ led.default_state = LEDS_GPIO_DEFSTATE_OFF;
+ }
+
ret = led_pwm_add(dev, priv, &led, fwnode);
if (ret) {
fwnode_handle_put(fwnode);
diff --git a/include/linux/leds_pwm.h b/include/linux/leds_pwm.h
index 93d101d28943..c9ef9012913d 100644
--- a/include/linux/leds_pwm.h
+++ b/include/linux/leds_pwm.h
@@ -10,6 +10,7 @@ struct led_pwm {
const char *default_trigger;
unsigned pwm_id __deprecated;
u8 active_low;
+ u8 default_state;
unsigned max_brightness;
unsigned pwm_period_ns;
};
--
2.25.1


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