Date:   Wed, 15 Dec 2021 21:46:06 +0100
From:   Pavel Machek <pavel@ucw.cz>
To:     Florian Eckert <fe@dev.tdt.de>
Cc:     robh+dt@kernel.org, linux-kernel@vger.kernel.org,
        linux-leds@vger.kernel.org, devicetree@vger.kernel.org
Subject: Re: [PATCH v2 1/2] leds: ktd20xx: Add the KTD20xx family of the RGB
 LEDs driver from Kinetic
Message-ID: <20211215204606.GH28336@duo.ucw.cz>
References: <20211123101826.9069-1-fe@dev.tdt.de>
 <20211123101826.9069-2-fe@dev.tdt.de>
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Hi!

> Introduce the KTD2061/58/59/60 RGB LEDs driver. The difference in these
> parts are the address number on the I2C bus the device is listen on.
>=20
> All KT20xx device could control up to 12 LEDs. The chip can be operated
> in two variants.
>=20
> Variant 1:
> The device has the ability to group LED outputs into two banks so that
> the two LED banks can be controlled with the same color. This could not
> be done via the LEDs 'sysfs' entry because of the limitation on the color
> register count. The color of the two banks can be configured via device
> 'sysfs' entry for all LEDs at once [current_color0|current_color1].
> Which color the LED is to be used can be set via the 'sysfs' of the
> individual LEDs via the 'multi_intensity' file. Valid values for the
> colors (RGB) are 0 | 1. The value 0 selects the color register 0 and the
> value 1 selects the color register 1.
>=20
> Variant 2:
> The device can also set the LED color independently. Since the chip only
> has two color registers, but we want to control the 12 LEDs
> independently via the 'led-class-multicolour' sysfs entry,
> the full RGB color depth cannot be used. Due to this limitation, only 7
> colors and the color black (off) can be set. To use this mode the color
> registers must be preset via the device tree or the device 'sysfs'. The
> color registers 0 must be preset with 0x00 (Red=3D0x00 Green=3D0x00 Blue=
=3D0x00).
> The color register1 should be preset all with the same value. This value
> depends on which light intensity is to be used in the setup.

Summary: some crazy hardware.

> +static ssize_t current_color0_store(struct device *dev,
> +		struct device_attribute *a,
> +		const char *buf, size_t size)
> +{

And now we have custom interface. Undocumented.

That is not acceptable, sorry.

Find a way to squeeze it into current RGB framework, perhaps with
reduced feature set.

AFAICT you could either pretend it is 2-LED driver with full 8bit RGB
on each, or you could pretend it is 12-LED driver with 1bit
RGB. Select one and implement that.

Best regards,
									Pavel
--=20
http://www.livejournal.com/~pavelmachek

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