FBdev application does not render anything

I just developed a lvgl applications which is correctly working through SDL2 and i want to try an fbdev/evdev version to obtain better perfomances.
I am able to compile an fbdev/evdev lvgl application but nothing is shown on my touchscreen.

Configuration is as follow:
#define LV_LINUX_FBDEV_BSD 0
#define LV_LINUX_FBDEV_RENDER_MODE LV_DISPLAY_RENDER_MODE_DIRECT
#define LV_LINUX_FBDEV_BUFFER_COUNT 1
#define LV_LINUX_FBDEV_BUFFER_SIZE 60
#define LV_LINUX_FBDEV_MMAP 1

This is the “initialization” code:

lv_group_set_default(lv_group_create());

lv_display_t *disp = lv_linux_fbdev_create();

lv_linux_fbdev_set_file(disp, "/dev/fb0");
    lv_display_set_resolution(disp, 320, 240);
lv_display_set_default(disp);

lv_indev_t *touch = lv_evdev_create(LV_INDEV_TYPE_POINTER, "/dev/input/event0");
lv_indev_set_group(touch, lv_group_get_default());
lv_indev_set_display(touch, disp);

Trying to get deeper in the problem i found that LVGL is always drawing zeroed buffers, any hint?