Add software blinking to GPIO LEDs

[blemouzy]

• Add software blinking to GPIO LEDs
• Add missing blink command to led shell

[blemouzy]

Comments are welcomed:

• Are k_timer the best choice to manage blinking delays?
• Is it a good idea to add a workqueue to call gpio_pin_set_dt function?

[simonguinot]

Hi @blemouzy,

Thanks for this PR but I can't agree with this.

The plan for software LED blinking is to implement a fallback at the LED core level. This way it will be available for ALL the LED drivers and not only led_gpio.

If a driver implements the blink API function (because the feature is supported by hardware) then it can be used directly else we can fall back on a software blinking mechanism (based on timer and/or workqueue).

For reference see the following discussions:

• #54594 (comment)
• #50511 (for color correction but the idea is the same)

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