Provide README section about backlight control

Author: tore-espressif

README.md

@@ -7,6 +7,7 @@ For a ready to use ESP32 project take look at the [lv_port_esp32](https://github
 - [Supported indev controllers](#supported-indev-controllers)
 - [Support for predefined development kits](#support-for-predefined-development-kits)
 - [Thread-safe I2C with I2C Manager](#thread-safe-i2c-with-i2c-manager)
+- [Backlight control](#backlight-control)
 
 **NOTE:** You need to set the display horizontal and vertical size, color depth and
 swap of RGB565 color on the LVGL configuration menuconfig (it's not handled automatically).
@@ -79,3 +80,14 @@ talk to devices on the I2C ports without getting in each other's way. These driv
 use a built-in copy of I2C Manager to talk to the I2C port, but you can also use 
 the I2C Manager component itself and have others play nice with LVGL and vice-versa.
 [Click here](i2c_manager/README.md) for details.
+
+
+## Backlight control
+
+Control of LCD's backlight is provided by separate module that is independent from the display driver.
+Configuration of the backlight controller can be found in menuconfig `LVGL ESP Drivers -> LVGL TFT Display controller`.
+
+There are three modes of operation:
+1. Off - No backlight control
+2. Switch - Allows ON/OFF control
+3. PWM - Allows brightness control (by Pulse-Width-Modulated signal)

lvgl_tft/esp_lcd_backlight.h

@@ -27,6 +27,7 @@ typedef void * disp_backlight_h;
 /**
  * @brief Configuration structure of backlight controller
  *
+ * Must be passed to disp_backlight_new() for correct configuration
  */
 typedef struct {
     bool pwm_control;
@@ -35,7 +36,7 @@ typedef struct {
 
     // Relevant only for PWM controlled backlight
     // Ignored for switch (ON/OFF) backlight control
-    int timer_idx; // ledc_timer_t
+    int timer_idx;   // ledc_timer_t
     int channel_idx; // ledc_channel_t
 } disp_backlight_config_t;