Physical LED Design Proposal

[Andrew Jeffery]

Hi Jayashree,

First up, apologies for the extreme length of time it took me to get to this.

On Fri, 27 May 2022, at 16:42, Jayashree D wrote:
> Hi Team,
>
> Problem Description :
>
> In the existing phosphor-led-sysfs design, it exposes one service per LED.
> Therefore, multiple services will be created for multiple GPIO pins
> configured for LED. To abstract this method and also to create LEDs under a
> single service, a new implementation is proposed.
>
> Existing Implementation :
>
> 1. Physical Leds are defined in the device tree under "leds" section.
> 2. Corresponding GPIO pin are defined for the physical LEDs.
> 3. "udev rules" are used to monitor the physical LEDs.
> 4. Once the LED in initialized in device tree, udev event will be created
> and it will trigger a systemd service for that LED.
> 5. Therefore, if multiple GPIO pins are configured for LEDs, then it will
> create a multiple systemd services
> (xyz.openbmc_project.led.controller at .service)
> for phosphor-led-sysfs based on the LED name.
>
> Example :
>
> busctl tree xyz.openbmc_project.LED.Controller.led1
> `-/xyz
>   `-/xyz/openbmc_project
>     `-/xyz/openbmc_project/led
>       `-/xyz/openbmc_project/led/physical
>         `-/xyz/openbmc_project/led/physical/led1
>
> busctl tree xyz.openbmc_project.LED.Controller.led2
> `-/xyz
>   `-/xyz/openbmc_project
>     `-/xyz/openbmc_project/led
>       `-/xyz/openbmc_project/led/physical
>         `-/xyz/openbmc_project/led/physical/led2
>
>
>
> New Implementation :
>
> 1. Physical Leds are defined in the device tree under "leds" section.
> 2. Corresponding GPIO pin are defined for the physical LEDs.
> 3. "udev rules" are used to monitor the physical LEDs.
> 4. Once the udev event is initialized for the LED, it will store those LED
> name using the script in udev instead of triggering systemd   service.
> 5. Phosphor-led-sysfs will have a single systemd service
> (xyz.openbmc_project.led.controller.service) running by default at system
> startup.
> 6. A dbus method call will be exposed from the service. udev will notify
> the LEDs detected in the driver.
>
> Example :
>
> busctl tree xyz.openbmc_project.LED.Controller
> `-/xyz
>   `-/xyz/openbmc_project
>     `-/xyz/openbmc_project/led
>       `-/xyz/openbmc_project/led/physical
>         `-/xyz/openbmc_project/led/physical/led1
>         `-/xyz/openbmc_project/led/physical/led2
>
>
> This was already discussed in the previous mail thread. Please refer to the
> below link.
> https://lists.ozlabs.org/pipermail/openbmc/2022-April/030272.html
>
> Please provide your suggestions on this new proposal.

This looks good to me.

Thanks.

Andrew