Messages in this thread | | | Date | Wed, 26 Jul 2017 20:42:23 +0800 | From | icenowy@aosc ... | Subject | Re: [linux-sunxi] [PATCH 10/10] ARM: dts: sun8i: Add SY8106A regulator to Orange Pi PC |
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在 2017-07-26 19:44,Maxime Ripard 写道: > Hi, > > On Wed, Jul 26, 2017 at 12:23:48PM +0200, Ondřej Jirman wrote: >> Hi, >> >> icenowy@aosc.io 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 seems that in regulator_desc structure a default value of ramp delay can be set, and the ones specified in dt can override it.
So just add .ramp_delay = 200 in the driver's regulator_desc part?
Should a comment be added that explains it's only an experienced value on Allwinner H3/H5 boards VDD-CPUX usage?
> > Maxime > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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