[PATCH v2 6/6] leds: lm3692x: Make sure we don't exceed the maximum led current

Guido Günther
2019-12-25T11:07:43Z

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 formular for the lm36923 is identical according to the data sheet.

Signed-off-by: Guido Günther <agx@sigxcpu.org>
---
drivers/leds/leds-lm3692x.c | 25 ++++++++++++++++++++++++-
1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/leds/leds-lm3692x.c b/drivers/leds/leds-lm3692x.c
index ff20560a8263..d7e5de8fe8db 100644
--- 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>
@@ -320,11 +321,29 @@ static int lm3692x_init(struct lm3692x_led *led)
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 */
+ if (led->brightness_ctrl & LM3692X_MAP_MODE_EXP) {
+ /* 228 =~ 1.0 / log2(1.003040572) */
+ max_code = ilog2(max_cur/50) * 228;
+ } else {
+ 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;
bool exp_mode;
int ret;

@@ -397,6 +416,10 @@ static int lm3692x_probe_dt(struct lm3692x_led *led)
return 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 = ":";
--
2.23.0