From 35b464e32c8bccef435e415db955787ead4ab44c Mon Sep 17 00:00:00 2001 From: Hugo Villeneuve Date: Sat, 22 Jul 2023 14:09:25 -0400 Subject: [PATCH] auxdisplay: hd44780: move cursor home after clear display command 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 Reviewed-by: Geert Uytterhoeven Tested-by: David Reaver Link: https://lore.kernel.org/r/20230722180925.1408885-1-hugo@hugovil.com Signed-off-by: Miguel Ojeda --- drivers/auxdisplay/hd44780_common.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/drivers/auxdisplay/hd44780_common.c b/drivers/auxdisplay/hd44780_common.c index 3934c2eebf33..7cbf375b0fa5 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);