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

Hugo Villeneuve
2023-07-25T15:14:07Z

On Mon, 24 Jul 2023 18:08:00 +0200
Geert Uytterhoeven <geert@linux-m68k.org> wrote:

> Hi Hugo,
>
> On Sat, Jul 22, 2023 at 8:18 PM Hugo Villeneuve <hugo@hugovil.com> wrote:
> > 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>
>
> Thanks for your patch!
>
> > --- 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);
>
> Sorry, I haven't tested your patch yet, as my HD44780 display is
> currently not connected to any system.
>
> Your patch LGTM, so
> Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
>
> Note that hd44780_common_home() calls hd44780_common_gotoxy().
> According to the documentation, both HD44780U and NHD-0220DZW-AG5
> support the Return Home command (0x02), so that could be a good
> alternative.

Hi Geert,
If this is desired, I think maybe it would be best to do it in a
separate patch. Maybe there is a good reason why hd44780_common_home()
calls hd44780_common_gotoxy() instead of using Return Home command?

Hugo.

>
> > }
> > EXPORT_SYMBOL_GPL(hd44780_common_clear_display);
>
> Gr{oetje,eeting}s,
>
> Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> -- Linus Torvalds
>