Re: [PATCH] arm64: dts: rockchip: add regulator-enable-ramp-delay to RK860-2/-3 regulators

[Quentin Schulz <quentin.schulz@cherry.de>]

Hi Heiko,

On 6/5/25 11:09 AM, Heiko Stübner wrote:
> Am Donnerstag, 5. Juni 2025, 10:57:13 Mitteleuropäische Sommerzeit schrieb Quentin Schulz:
>> Hi Heiko,
>>
>> On 6/4/25 10:24 PM, Heiko Stuebner wrote:
[...]
>>> And in fact the datasheet for the regulator defines an "Internal soft-start
>>> time". For a target output voltage of 1.0V the _typical_ time to reach at
>>> least 92% of the output is given as 260uS.
>>>
>>
>> Indeed. Now looking at the existing Device Trees, it seems some set the
>> ramp-up delay already, but to 2300 and not 500 like suggested here.
>> Maybe it'd be safer to go for 2300 by default then?
> 
> enable-ramp-delay is a totally different beast than the ramp-delay.
> ramp-delay is needed when changing the running voltage and uses a unit
> of "uV/us", so microvolt per microsecond ... where the enable-ramp-delay
> is the one for enabling the regulator and uses uS.

Thanks for the explanation.

[...]

>>> mainline right now. I've chosen 500uS to be on the safe side, as
>>> 260uS is the "typical" value for 1.0V and sadly no max value is given
>>> in the datasheet.
>>>
>>
>> Reading the rk808 regulator driver... maybe we should also set the
>> typical delay as default in the fan53555.c driver? See rk805_reg which
>> sets the enable_time for some (typically the LDO with 400 and the DCDC
>> at 0). I assume those can be overridden from the DT anyway, but at least
>> we would have some decently safe defaults?
>>
>> If we do not do this, then we should probably force the presence of
>> regulator-ramp-delay property for the rk860x DT binding so we don't
>> forget for future Device Trees?
> 
> that is scope-creep (rk808 != rk860) ... but I find the idea of trying to

I was just hinting at the possibility to set a default enable_time if 
one's missing from the Device Tree because the rk808 driver seems to be 
doing something like that. rk860-x is indeed supported by a different 
driver, which doesn't set this by default, hence my suggestion :)

> set the enable-ramp-delay as required for the rk860-x interesting :-) .
> 

But incompatible with the "default in driver" approach :) So one or the 
other :)

Cheers,
Quentin