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

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Message-ID: <ZL/7f8Q6xnoJVakk@1wt.eu>
Date:   Tue, 25 Jul 2023 18:42:39 +0200
From:   Willy Tarreau <w@....eu>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Hugo Villeneuve <hugo@...ovil.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Hugo Villeneuve <hvilleneuve@...onoff.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] auxdisplay: hd44780: move cursor home after clear
 display command

On Tue, Jul 25, 2023 at 05:58:45PM +0200, Geert Uytterhoeven wrote:
> > One thing I'm having in mind is that this LCD supported horizontal
> > scrolling to show the off-screen columns. I'm wondering if the gotoxy()
> > and home() did the same thing regarding this. Maybe gotoxy() scrolled
> > back to 0,0 while home() just moved the cursor to the visible home
> > without scrolling back, in which case it could make a difference.
> 
> Indeed, at least according to the real HD44780 documentation,
> Return Home also resets the scrolling.

OK, thanks for checking!

> > I would suggest that we just stick to the specs and see if anyone reports
> > any trouble. There are so many compatible devices nowadays that possibly
> > implement only a subset of the original controller that we should really
> > stick to what is clearly understood by everyone and not rely on some old
> > conclusions about vague observations made by me 25 years ago!
> 
> OK. Given this patch is also a workaround for an incomplete
> implementation, let's keep hd44780_common_home() as-is.

OK, works for me.

Thanks,
Willy