auxdisplay: hd44780: move cursor home after clear display command

35b464e3 · Hugo Villeneuve <[email protected]> · 2023-07-22 14:09:25 -04:00

The DISPLAY_CLEAR command on the NewHaven NHD-0220DZW-AG5 display
does NOT change the DDRAM address to 00h (home position) like the
standard Hitachi HD44780 controller. As a consequence, the starting
position of the initial string LCD_INIT_TEXT is not guaranteed to be
at 0,0 depending on where the cursor was before the DISPLAY_CLEAR
command.

Extract of DISPLAY_CLEAR command from datasheets of:

    Hitachi HD44780:
        ... It then sets DDRAM address 0 into the address counter...

    NewHaven NHD-0220DZW-AG5 datasheet:
	... This instruction does not change the DDRAM Address

Move the cursor home after sending DISPLAY_CLEAR command to support
non-standard LCDs.

Signed-off-by: Hugo Villeneuve <[email protected]>
Reviewed-by: Geert Uytterhoeven <[email protected]>
Tested-by: David Reaver <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Miguel Ojeda <[email protected]>

Commit: 35b464e32c8bccef435e415db955787ead4ab44c
Parents: 2ccdd1b1

Changes

1 files changed · +9 −1

File	Status	Add	Del	Content
drivers/auxdisplay/hd44780_common.c	modified	+9	−1	View file

drivers/auxdisplay/hd44780_common.c

View file

diff --git a/drivers/auxdisplay/hd44780_common.c b/drivers/auxdisplay/hd44780_common.c
index 3934c2e..7cbf375 100644
--- a/drivers/auxdisplay/hd44780_common.c
+++ b/drivers/auxdisplay/hd44780_common.c
@@ -82,7 +82,15 @@ int hd44780_common_clear_display(struct charlcd *lcd)
 	hdc->write_cmd(hdc, LCD_CMD_DISPLAY_CLEAR);
 	/* datasheet says to wait 1,64 milliseconds */
 	long_sleep(2);
-	return 0;
+
+	/*
+	 * The Hitachi HD44780 controller (and compatible ones) reset the DDRAM
+	 * address when executing the DISPLAY_CLEAR command, thus the
+	 * following call is not required. However, other controllers do not
+	 * (e.g. NewHaven NHD-0220DZW-AG5), thus move the cursor to home
+	 * unconditionally to support both.
+	 */
+	return hd44780_common_home(lcd);
 }
 EXPORT_SYMBOL_GPL(hd44780_common_clear_display);
 