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| author | Hugo Villeneuve <hvilleneuve@dimonoff.com> | 2023-07-22 14:09:25 -0400 |
|---|---|---|
| committer | Miguel Ojeda <ojeda@kernel.org> | 2023-08-19 21:53:49 +0200 |
| commit | 35b464e32c8bccef435e415db955787ead4ab44c (patch) | |
| tree | b27ebda1c8800c497743de3b8fee774ab3db13dc /drivers/auxdisplay | |
| parent | 2ccdd1b13c591d306f0401d98dedc4bdcd02b421 (diff) | |
| download | linux-35b464e32c8bccef435e415db955787ead4ab44c.tar.gz | |
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 <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>
Diffstat (limited to 'drivers/auxdisplay')
| -rw-r--r-- | drivers/auxdisplay/hd44780_common.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/drivers/auxdisplay/hd44780_common.c b/drivers/auxdisplay/hd44780_common.c index 3934c2eebf33d..7cbf375b0fa5e 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); |