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auxdisplay: hd44780: move cursor home after clear display command

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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>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: David Reaver <me@davidreaver.com>
Link: https://lore.kernel.org/r/20230722180925.1408885-1-hugo@hugovil.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Hugo Villeneuve 2023-07-22 14:09:25 -04:00 committed by Miguel Ojeda
parent 2ccdd1b13c
commit 35b464e32c
1 changed files with 9 additions and 1 deletions
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10
drivers/auxdisplay/hd44780_common.c
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@ -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);