6.1-stable review patch. If anyone has any objections, please let me know.
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From: Hugo Villeneuve hvilleneuve@dimonoff.com
commit 35b464e32c8bccef435e415db955787ead4ab44c upstream.
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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/auxdisplay/hd44780_common.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
--- a/drivers/auxdisplay/hd44780_common.c +++ b/drivers/auxdisplay/hd44780_common.c @@ -82,7 +82,15 @@ int hd44780_common_clear_display(struct 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);