[PATCH v2] auxdisplay: hd44780: move cursor home after clear display command

Hugo Villeneuve
2023-07-22T18:09:35Z

From: Hugo Villeneuve <hvilleneuve@dimonoff.com>

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 <hvilleneuve@dimonoff.com>
---
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);

base-commit: d192f5382581d972c4ae1b4d72e0b59b34cadeb9
--
2.30.2