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SubjectRe: [PATCH v2 31/32] auxdisplay: charlcd: Do not print chars at end of line
On Tue, Sep 22, 2020 at 11:44:22AM +0200, Lars Poeschel wrote:
> On Tue, Sep 22, 2020 at 07:27:01AM +0200, Willy Tarreau wrote:
> > On Mon, Sep 21, 2020 at 04:46:43PM +0200, wrote:
> > > From: Lars Poeschel <>
> > >
> > > Skip printing characters at the end of a display line. This fits to the
> > > behaviour we already had, that the cursor is nailed to last position of
> > > a line.
> >
> > Just very old memories, but wasn't this used with the ability to shift
> > the display ? IIRC the HD44780 has a 2x64 chars buffer and you can make
> > the buffered characters appear when you shift the display. That's akin
> > to seeing the display as an adjustable window over the buffer. I don't
> > remember having used that feature, so if it didn't previously work, please
> > disregard my comment, I just want to be sure we don't break a feature
> > others might be relying on.
> Yes, indeed. But this is a point, where this was inconsistent. The
> feature you described worked only for displays with 2 lines or less. On
> displays with 4 lines there simply is no buffer that is not visible and
> in this case it sticks to the end of the line already.


> To make this work for all displays this would require a whole lot of
> work. We would need a fallback implementation that emulates this in
> software and then redraws the whole display from that software
> (linux-side) buffer when shifting.

I don't think that's worth it at all, really!

> Currently my patchset cuts this feature for displays with one or two
> lines. I don't see clean an easy way to leave that in. Any ideas ?

The points you mention are good enough indicators that it's extremely
unlikely anyone has ever used that feature with these drivers. So I
think it's best to keep your changes and wait to see if anyone pops
up with an obscure use case, in which case their explanation might
help figure another approach.


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