Maxime Ripard píše v St 26. 07. 2017 v 13:44 +0200: > Hi, > > On Wed, Jul 26, 2017 at 12:23:48PM +0200, Ondřej Jirman wrote: > > Hi, > > > > icenowy@xxxxxxx píše v St 26. 07. 2017 v 15:36 +0800: > > > > > > > > > > > > > > > Otherwse > > > > > > > > > > > > > + regulator-max-microvolt = <1400000>; > > > > > > > + regulator-ramp-delay = <200>; > > > > > > > > > > > > Is this an actual constraint of the SoC? Or is it a characteristic > > > > > > of the regulator? If it is the latter, it belongs in the driver. > > > > > > AFAIK the regulator supports varying the ramp delay (slew rate). > > > > > > I don't know... > > > > > > Maybe I should ask Ondrej? > > > > It is probably neither. > > > > It is used to calculate a delay inserted by the kernel between setting > > a new target voltage over I2C and changing the frequency of the CPU. > > The actual delay is calculated by the difference between previous and > > the new voltage. > > > > I don't remember seeing anything in the datasheet of the regulator. > > This is just some low value that works. > > > > It would probably be dependent on the capacitance on the output of the > > regulator, actual load (which varies), etc. So it is a board specific > > value. One could measure it with an oscilloscope if there's a need to > > optimize this. > > If this is a reasonable default, then this should be in the > driver. You can't expect anyone to properly calculate a ramp delay and > have access to both a scope and the CPU power lines. It translates to 1ms per 0.2V which is highly conservative. The real times will be in 1-10us range. So I guess this could be a default in the driver. regards, o. > Maxime > > -- > Maxime Ripard, Free Electrons > Embedded Linux and Kernel engineering > http://free-electrons.com >
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