linux-kernel - Re: [PATCH] video: hd44780: Add hd44780 lcd display driver

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Date:   Thu, 07 Dec 2017 09:33:21 +0100
From:   Lars Poeschel <poeschel@...onage.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     David Airlie <airlied@...ux.ie>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Manuel Schölling <manuel.schoelling@....de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Stafford Horne <shorne@...il.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        Randy Dunlap <rdunlap@...radead.org>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Sean Paul <seanpaul@...omium.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH] video: hd44780: Add hd44780 lcd display driver

On Wed, Dec 6, 2017 at 16:04:10 CET Geert Uytterhoeven wrote:
> Hi Lars,
> 
> On Wed, Dec 6, 2017 at 2:52 PM, Lars Poeschel <poeschel@...onage.de> wrote:
> > This adds a console driver for hd44780 based character lcd displays and
> > clones. The driver currently supports 20x4 character displays with
> > character ROMs A00 and A02.
> > The hardware wirings to the display have to be supplied to the kernel in
> > the devicetree. The binding doc has the necessary information.
> > There are also tons of these cheap displays sold with a serial
> > interface. Many of them use a simple pcf8574 gpio expanders. An example
> > for using that kind of display is also in the binding doc.
> > 
> > Signed-off-by: Lars Poeschel <poeschel@...onage.de>
> 
> Thanks for your patch!
> 
> > ---
> > 
> >  .../bindings/video/console/hd44780con.txt          |  42 ++
> >  drivers/video/console/Kconfig                      |  13 +
> >  drivers/video/console/Makefile                     |   1 +
> >  drivers/video/console/hd44780con.c                 | 676
> >  +++++++++++++++++++++
> I'm wondering if you could implement this on top of the existing charlcd
> framework:
> 
>     drivers/auxdisplay/charlcd.c
>     include/misc/charlcd.h
> 
> which can use the existing hd44780 backend:
> 
>     Documentation/devicetree/bindings/auxdisplay/hit,hd44780.txt
>     drivers/auxdisplay/hd44780.c
> 
> That way it can be used on other character LCDs, like the one supported by
> drivers/auxdisplay/panel.c.

Oh! Yes, this is a very interesting idea! This would involve multiple steps 
until this would be useful for me, but I will definitely have a look at this!
So, please drop my patch for now. If for some reason in the future I find, 
that it should go upstream, I will submit it again.

BTW thanks for the hint about the hd44780 charlcd backend. I did not know 
about this. My hd44780 console driver is quite a bit old. I just found time to 
clean up, rebase, test and submit it now.

Regards,
Lars