z2_plus: lights: Scale LCD brightness if needed

Change-Id: I7aade9ee626811e408e7f2d66b169a12695a27f6
Signed-off-by: Davide Garberi <dade.garberi@gmail.com>

1 files changed, 53 insertions, 0 deletions

diff --git a/liblight/lights.c b/liblight/lights.c
index 1f74712..3f3a1cf 100644
--- a/liblight/lights.c
+++ b/liblight/lights.c
@@ -54,6 +54,9 @@ static const char BLUE_LED_FILE[]
 static const char LCD_FILE[]
         = "/sys/class/leds/lcd-backlight/brightness";
 
+static const char LCD_MAX_BRIGHTNESS_FILE[]
+        = "/sys/class/leds/lcd-backlight/max_brightness";
+
 static const char RED_DUTY_PCTS_FILE[]
         = "/sys/class/leds/red/duty_pcts";
 
@@ -116,6 +119,9 @@ static int BRIGHTNESS_RAMP[RAMP_SIZE]
         = { 0, 12, 25, 37, 50, 72, 85, 100 };
 #define RAMP_STEP_DURATION 50
 
+#define DEFAULT_MAX_BRIGHTNESS 255
+int max_brightness;
+
 /**
  * device methods
  */
@@ -126,6 +132,38 @@ void init_globals(void)
     pthread_mutex_init(&g_lock, NULL);
 }
 
+static int read_int(char const* path)
+{
+    int fd, len;
+    int num_bytes = 10;
+    char buf[11];
+    int retval;
+
+    fd = open(path, O_RDONLY);
+    if (fd < 0) {
+        ALOGE("%s: failed to open %s\n", __func__, path);
+        goto fail;
+    }
+
+    len = read(fd, buf, num_bytes - 1);
+    if (len < 0) {
+        ALOGE("%s: failed to read from %s\n", __func__, path);
+        goto fail;
+    }
+
+    buf[len] = '\0';
+    close(fd);
+
+    // no endptr, decimal base
+    retval = strtol(buf, NULL, 10);
+    return retval == 0 ? -1 : retval;
+
+fail:
+    if (fd >= 0)
+        close(fd);
+    return -1;
+}
+
 static int
 write_int(char const* path, int value)
 {
@@ -193,6 +231,15 @@ set_light_backlight(struct light_device_t* dev,
     if(!dev) {
         return -1;
     }
+
+    // If max panel brightness is not the default (255),
+    // apply linear scaling across the accepted range.
+    if (max_brightness != DEFAULT_MAX_BRIGHTNESS) {
+        int old_brightness = brightness;
+        brightness = brightness * max_brightness / DEFAULT_MAX_BRIGHTNESS;
+        ALOGV("%s: scaling brightness %d => %d\n", __func__, old_brightness, brightness);
+    }
+
     pthread_mutex_lock(&g_lock);
     err = write_int(LCD_FILE, brightness);
     pthread_mutex_unlock(&g_lock);
@@ -424,6 +471,12 @@ static int open_lights(const struct hw_module_t* module, char const* name,
     else
         return -EINVAL;
 
+    max_brightness = read_int(LCD_MAX_BRIGHTNESS_FILE);
+    if (max_brightness < 0) {
+        ALOGE("%s: failed to read max panel brightness, fallback to 255!\n", __func__);
+        max_brightness = DEFAULT_MAX_BRIGHTNESS;
+    }
+
     pthread_once(&g_init, init_globals);
 
     struct light_device_t *dev = malloc(sizeof(struct light_device_t));