linux-kernel - Re: [PATCH v2 18/18] auxdisplay: ht16k33: Add segment display LED support

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Message-ID: <CAMuHMdV5fywjF63MqE_SqfumwN3EY=jBTEiMfqbjFO12c_nj0Q@mail.gmail.com>
Date:   Mon, 28 Jun 2021 11:21:04 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Marek Behun <marek.behun@....cz>
Cc:     Robin van der Gracht <robin@...tonic.nl>,
        Rob Herring <robh+dt@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Paul Burton <paulburton@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Pavel Machek <pavel@....cz>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-leds <linux-leds@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 18/18] auxdisplay: ht16k33: Add segment display LED support

Hi Marek,

On Fri, Jun 25, 2021 at 10:39 PM Marek Behun <marek.behun@....cz> wrote:
> On Fri, 25 Jun 2021 14:59:02 +0200
> Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>
> > Instantiate a single LED for a segment display.  This allows the user to
> > control display brightness and blinking through the LED class API and
> > triggers, and exposes the display color.
> > The LED will be named "auxdisplay:<color>:backlight".
>
> What if there are multiple "auxdisplay"s ?

I understand the LED core will just add a suffix on a name collision.

> Doesn't this subsystem have IDs? So that you can use auxdisplayN for
> device name, for example?

Auxdisplay does not have IDs, as there is no subsystem to register
with.  It's just a collection of drivers for auxiliary displays with
no common API.  Some drivers use fbdev, others use a chardev, or an
attribute file in sysfs.

BTW, I just followed Pavel's advice in naming.

> > +     of_property_read_u32(node, "color", &color);
> > +     seg->led.name = devm_kasprintf(dev, GFP_KERNEL,
> > +                     "auxdisplay:%s:" LED_FUNCTION_BACKLIGHT,
> > +                     color < LED_COLOR_ID_MAX ? led_colors[color] : "");
>
> If you use devm_led_classdev_register_ext and pass struct
> led_init_data, LED core will generate name of the LED itself.

Will that make any difference, except for adding more code?
Looking at the implementation, I still have to use devm_kasprintf()
to combine color and function for led_init_data.default_label?

Gr{oetje,eeting}s,

                        Geert

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