linux-kernel - Re: RGB LED control (was Re: "advanced" LED controllers)

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Date:	Mon, 9 Mar 2015 09:08:37 +0100
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Pavel Machek <pavel@....cz>
Cc:	Alexandre Courbot <gnurou@...il.com>, Felipe Balbi <balbi@...com>,
	Bryan Wu <cooloney@...il.com>,
	Richard Purdie <rpurdie@...ys.net>,
	"linux-leds@...r.kernel.org" <linux-leds@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: RGB LED control (was Re: "advanced" LED controllers)

Hi Pavel,

On Sun, Mar 8, 2015 at 9:57 PM, Pavel Machek <pavel@....cz> wrote:
> Ok, so I played with RGB LED a bit, and we have quite a gap in
> documentation: what 50% brightness means is non-trivial and very
> important in case we want to do smooth blinking and color transitions.
>
> Signed-off-by: Pavel Machek <pavel@....cz>
>
> diff --git a/Documentation/ABI/testing/sysfs-class-led b/Documentation/ABI/testing/sysfs-class-led
> index 3646ec8..649d7a6 100644
> --- a/Documentation/ABI/testing/sysfs-class-led
> +++ b/Documentation/ABI/testing/sysfs-class-led
> @@ -8,6 +8,11 @@ Description:
>                 non-zero brightness settings. The value is between 0 and
>                 /sys/class/leds/<led>/max_brightness.
>
> +               If LED supports continuous brightness settings, 50% brightness
> +               should correspond to 50% brightness perceived by human, in a similar
> +               manner pixel brightness on monitor does (not 50% PWM).

How many drivers do it right? How many don't?

For those that don't, perhaps we handle the conversion between perceived and
pwm in the core, e.g. by adding a new flag to led_classdev.flags to indicate
the need for conversion?

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
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