Debug

FBTFT has dynamic debug support. This is enabled when loading the device or through sysfs when the driver is loaded.

sudo modprobe fbtft_device name=itdb28 debug=1
echo "5" > /sys/class/graphics/fb1/debug

Debug output can be turned on for individual functions setting bits. There is 7 shorthand debug levels 1-7.

The debug ouput goes to the kernel log. Can be viewed with dmesg

Here is the macros from fbtft.h

/* shorthand debug levels */
#define DEBUG_LEVEL_1	DEBUG_REQUEST_GPIOS
#define DEBUG_LEVEL_2	(DEBUG_LEVEL_1 | DEBUG_DRIVER_INIT_FUNCTIONS | DEBUG_TIME_FIRST_UPDATE)
#define DEBUG_LEVEL_3	(DEBUG_LEVEL_2 | DEBUG_RESET | DEBUG_INIT_DISPLAY | DEBUG_BLANK | DEBUG_FREE_GPIOS | DEBUG_VERIFY_GPIOS | DEBUG_BACKLIGHT | DEBUG_SYSFS)
#define DEBUG_LEVEL_4	(DEBUG_LEVEL_2 | DEBUG_FB_READ | DEBUG_FB_WRITE | DEBUG_FB_FILLRECT | DEBUG_FB_COPYAREA | DEBUG_FB_IMAGEBLIT | DEBUG_FB_BLANK)
#define DEBUG_LEVEL_5	(DEBUG_LEVEL_3 | DEBUG_UPDATE_DISPLAY)
#define DEBUG_LEVEL_6	(DEBUG_LEVEL_4 | DEBUG_LEVEL_5)
#define DEBUG_LEVEL_7	0xFFFFFFFF

#define DEBUG_DRIVER_INIT_FUNCTIONS (1<<3)
#define DEBUG_TIME_FIRST_UPDATE     (1<<4)
#define DEBUG_TIME_EACH_UPDATE      (1<<5)
#define DEBUG_DEFERRED_IO           (1<<6)
#define DEBUG_FBTFT_INIT_FUNCTIONS  (1<<7)

/* fbops */
#define DEBUG_FB_READ               (1<<8)
#define DEBUG_FB_WRITE              (1<<9)
#define DEBUG_FB_FILLRECT           (1<<10)
#define DEBUG_FB_COPYAREA           (1<<11)
#define DEBUG_FB_IMAGEBLIT          (1<<12)
#define DEBUG_FB_SETCOLREG          (1<<13)
#define DEBUG_FB_BLANK              (1<<14)

#define DEBUG_SYSFS                 (1<<16)

/* fbtftops */
#define DEBUG_BACKLIGHT             (1<<17)
#define DEBUG_READ                  (1<<18)
#define DEBUG_WRITE                 (1<<19)
#define DEBUG_WRITE_VMEM            (1<<20)
#define DEBUG_WRITE_DATA_COMMAND    (1<<21)
#define DEBUG_SET_ADDR_WIN          (1<<22)
#define DEBUG_RESET                 (1<<23)
#define DEBUG_MKDIRTY               (1<<24)
#define DEBUG_UPDATE_DISPLAY        (1<<25)
#define DEBUG_INIT_DISPLAY          (1<<26)
#define DEBUG_BLANK                 (1<<27)
#define DEBUG_REQUEST_GPIOS         (1<<28)
#define DEBUG_FREE_GPIOS            (1<<29)
#define DEBUG_REQUEST_GPIOS_MATCH   (1<<30)
#define DEBUG_VERIFY_GPIOS          (1<<31)

With Bash shell it's easy to set the individual bits:

# DEBUG_LEVEL_1, DEBUG_FB_BLANK, DEBUG_BLANK
sudo modprobe fbtft_device name=itdb28 debug=$((1 | 1<<14 | 1<<27))

# DEBUG_FB_SETCOLREG
echo $((1<<13)) > /sys/class/graphics/fb1/debug

Driver in kernel

If the driver is compiled into the kernel, the debug argument is set on the kernel command line

Add to /boot/cmdline.txt

fbtft.debug=1