[Letux-kernel] Status of JZ4780/CI20 upstream support

Paul Boddie paul at boddie.org.uk
Sat Jul 13 01:47:23 CEST 2019

On Monday 8. July 2019 16.12.48 Paul Boddie wrote:
> I was going to look at USB today, seeing what it would take to get the
> JZ4780- specific host drivers working with a newer kernel than 3.18. The
> initial motivation was to make the main LED responsive since it appears to
> be connected to a pin designated for USB VBUS:
> https://www.elinux.org/CI20_Hardware#LED
> I am imagining that if the USB drivers are actually in place, their
> activation and deactivation will also cause the pin to change value and
> thereby cause the LED to switch off upon shutdown.

Actually, in terms of the LED illumination, I think the USB drivers are a 
distraction (albeit a useful one, ultimately). The real problem is the lack of 
interaction with the power management IC (ACT8600, according to the schematics 
and the 3.18 device tree).

In the 5.1.x device tree for the CI20, since there are no mechanisms defined 
for I2C signalling with the PMIC, the 3.3V I/O supply does not get 
disconnected upon shutdown, leaving the LED on if the board power is still 
connected. This I2C signalling seems to use the dedicated JZ4780 peripheral 
support in the 3.18 kernel, and this driver does still seem to be present in 
the 5.1.x series at least. Although the PMIC driver has not been carried 
forward, there appears to be another which claims to support the ACT8600.

So I imagine that I need to figure out how to get the power management and I2C 
definitions right so that the different power supplies are enabled and 
disabled at the appropriate times.


P.S. Sorry for the reply to myself and general lack of coherent progress!

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