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In-Reply-To: <1ef07be4-6706-5071-f992-acbc43e2116f@gmail.com>
From: "Milton Miller II" <miltonm@us.ibm.com>
To: "S.Nishikawa" <nishikawa.shun@gmail.com>
Date: Sun, 4 Oct 2020 18:34:59 +0000
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Subject: Re:  LED accessed via I2C
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On October 4, 2020 around 4:05am in some timezone, S.Nishikawa wrote:
>Hi,
>
>In our hardware, the Alert LED is attached to the end of the CPLD and
>is=20
>accessed via I2C. I think phosphor-led-sysfs controls LEDs with GPIO,
>
>but how can I control the LED beyond I2C?


Actually phosphor-led-manager will control any device that has a=20
kernel driver exposing the LED interface.  For PCA i2c devices=20
we tend to expose all the pins as gpio then individual gpios as
gpio led devices because the led subsystem will change the led=20
instance number based on which pins of the package are LED.

It sounds like your cpld has a custom interface.  If the leds
can be controlled via a separate i2c addressed endpoint I would=20
suggest a multi-function device binding using the mfd subsystem.
If it is directly controled by a register consider registering=20
a regmap like many voltage monitor and control devices.  One=20
advantage of regmap is it provides both locking and caching of=20
the values written, controllable on a per-register basis.

You will need a kernel driver for the remaining function that=20
is accessible over the i2c interface.

See https://www.kernel.org/doc/html/latest/leds/leds-class.html#
for information on the kernel LED subsystem.

I hope this gets you headed in a productive direction.
milton