leds: lm3692x: Make sure we don't exceed the maximum LED current

The current is given by the formular from page 12 of
https://www.ti.com/lit/ds/symlink/lm36922.pdf. We use this to limit the
led's max_brightness using the led-max-microamp DT property.

The formula for the lm36923 is identical according to the data sheet.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

diff --git a/drivers/leds/leds-lm3692x.c b/drivers/leds/leds-lm3692x.c
index 28973cc..1b056af 100644 (file)
--- a/drivers/leds/leds-lm3692x.c
+++ b/drivers/leds/leds-lm3692x.c
@@ -6,6 +6,7 @@
 #include <linux/i2c.h>
 #include <linux/init.h>
 #include <linux/leds.h>
+#include <linux/log2.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/of.h>
@@ -321,11 +322,24 @@ out:
        return ret;
 }
 
+static enum led_brightness lm3692x_max_brightness(struct lm3692x_led *led,
+                                                 u32 max_cur)
+{
+       u32 max_code;
+
+       /* see p.12 of LM36922 data sheet for brightness formula */
+       max_code = ((max_cur * 1000) - 37806) / 12195;
+       if (max_code > 0x7FF)
+               max_code = 0x7FF;
+
+       return max_code >> 3;
+}
+
 static int lm3692x_probe_dt(struct lm3692x_led *led)
 {
        struct fwnode_handle *child = NULL;
        struct led_init_data init_data = {};
-       u32 ovp;
+       u32 ovp, max_cur;
        int ret;
 
        led->enable_gpio = devm_gpiod_get_optional(&led->client->dev,
@@ -391,6 +405,10 @@ static int lm3692x_probe_dt(struct lm3692x_led *led)
                return ret;
        }
 
+       ret = fwnode_property_read_u32(child, "led-max-microamp", &max_cur);
+       led->led_dev.max_brightness = ret ? LED_FULL :
+               lm3692x_max_brightness(led, max_cur);
+
        init_data.fwnode = child;
        init_data.devicename = led->client->name;
        init_data.default_label = ":";