linux-kernel - Re: Linux support for a 7 segment LED display

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Message-ID: <CAMuHMdVPcty_O5uwTv6eBNwt_PNviKwjpjmfiOF05tqNW_CA4g@mail.gmail.com>
Date: Fri, 23 Feb 2024 08:53:01 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Pavel Machek <pavel@....cz>
Cc: Chris Packham <Chris.Packham@...iedtelesis.co.nz>, 
	Andy Shevchenko <andy.shevchenko@...il.com>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, "lee@...nel.org" <lee@...nel.org>, 
	"linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Linux support for a 7 segment LED display

Hi Pavel,

On Fri, Feb 23, 2024 at 8:47 AM Pavel Machek <pavel@....cz> wrote:
> > > Right, but also with some additional properties, like
> > > - type of the indicator (7, 14, etc segments, for now we have only
> > > these two supported)
> > > - use-dot (+1 led per each digit)
> > > - characters (how many digits we have, so we need respective amount of GPIOs)
> > >
> > > With this it's indeed belongs directly to auxdisplay as we have almost
> > > everything is done already there.
> >
> > I've been playing about with this. I've got an auxdisplay driver that's
> > basically working (I won't bother spamming list with it yet). But I'm
> > wondering how I'd represent multiple characters. I kind of feel the
> > natural representation would be something like.
> >
> >          led-7seg {
> >                  compatible = "generic,7-segment-on-gpio";
> >                  char-0 {
> >                      segment-gpios = <&gpio 0 GPIO_ACTIVE_LOW
> >                                       &gpio 1 GPIO_ACTIVE_LOW
> >                                       &gpio 2 GPIO_ACTIVE_LOW
> >                                       &gpio 3 GPIO_ACTIVE_LOW
> >                                       &gpio 4 GPIO_ACTIVE_LOW
> >                                       &gpio 5 GPIO_ACTIVE_LOW
> >                                       &gpio 6 GPIO_ACTIVE_LOW>;
> >                  };
> >                  char-1 {
> >                      segment-gpios = <&gpio 8 GPIO_ACTIVE_LOW
> >                                       &gpio 9 GPIO_ACTIVE_LOW
> >                                       &gpio 10 GPIO_ACTIVE_LOW
> >                                       &gpio 11 GPIO_ACTIVE_LOW
> >                                       &gpio 12 GPIO_ACTIVE_LOW
> >                                       &gpio 13 GPIO_ACTIVE_LOW
> >                                       &gpio 14 GPIO_ACTIVE_LOW>;
> >                  };
> >          };
> >
> > But having those sub-nodes means I can't just use devm_gpiod_get_array()
> > instead I'd have to use device_for_each_child_node() and
> > devm_fwnode_gpiod_get_index(). Am I missing something? I could do away
> > with the sub-nodes and have properties like "segment-0-gpios",
> > "segment-1-gpios" but that feels awkward.
>
> One solution would be to treat separate digits as separata devices
> :-).

That's definitely an option, but would prevent you from having a
single display using auxdisplay/line-display.

> Other would be saying you don't have hardware for that, and make it
> someone else's future problem.

;-)

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68korg

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