[Issue-51]: enable pwm from device tree

[jempatel]

• do not claim pwm pins

[greenbreakfast]

thanks @jempatel, merging this in (cc OnionIoT/OpenWRT-Packages#51)
Will make a release here and then build new beta firmware afterwards.

So we don't need the second patch that @plan44 uses in https://github.com/plan44/plan44-feed/blob/main/p44b-onion/p44build/global-patches/204-mt7628an-pwm-irq.diff ?

[jempatel]

thanks @jempatel, merging this in (cc OnionIoT/OpenWRT-Packages#51) Will make a release here and then build new beta firmware afterwards.

So we don't need the second patch that @plan44 uses in https://github.com/plan44/plan44-feed/blob/main/p44b-onion/p44build/global-patches/204-mt7628an-pwm-irq.diff ?

Yes, It sets interrupt from dts file, so I am not sure about its use case. For PWM to work, We needed two changes

1. enable pwm from dts, which we tracked from the sources repo of the old version.
2. enabling pwm causes a pin claimed issue, and a patch from plan44 worked with that, and after applying that patch sysfs for pwmchip0 was created.

[plan44]

Yes, It sets interrupt from dts file, so I am not sure about its use case.

Its documentary at this time, as the current PWM driver does not make use of interrupts.

But knowing how PWM interrupts are connected in the MT7688 chip is a valuable documentation nugget!

Back in 2017 (when I started writing p44ledchain) I spent days figuring out what IRQ the PWM unit might use. This is not poperly documented anywhere, not even in the MT7688 datasheet. I finally found the number 26 mentioned in the datasheet for the MT7628 (different, but similar enough SoC), and verified it actually is the same in MT7688...