Hi! > > >> For folks hacking on Pixel Cs (which is now outside of Google's official > > >> support window for Android) and customizing their own kernel and > > >> userspace > > >> this would be acceptable, but we wanted to expose this feature in the > > >> power supply properties because the feature does exist in the Emedded > > >> Controller firmware of the Pixel C and all of Google's Chromebooks with > > >> USB-C made since 2015 in case someone running an up to date kernel wanted > > >> to limit the charging power for thermal or other reasons. > > >> > > >> This patch exposes a new property, similar to input current limit, to > > >> re-configure the maximum voltage from the external supply at runtime > > >> based on system-level knowledge or user input. > > > > > > Could we get power input limit, instead? > > > > > > > I'm open but I have some concerns, so lets discuss a bit about it :) > > > > According to the USB PD 2.0 specs if we limit the source at 15W we can get > > 5V/3A > > or 9V/1.67A, if I am not mistaken the higher voltage caused problem since > > the > > conversion to lower internal voltages generated more heat, so in this case > > 9V/1.67A is not a valid value for us (maybe someone from ChromeOS can > > confirm > > this?).
> Around Xmas are bad dates to start a discussion. I don't want this
> patch will be forgotten, so a gentle ping on your thoughts on this :)
> (just in case)
If someone can indeed confirm it is _voltage_ that is problematic,
then approach is ok with me. [But I'd not expect buck convertor
efficiency to differ greatly based on input voltage.]
Best regards,
Pavel
> > >> +What:
> > >> /sys/class/power_supply/<supply_name>/input_voltage_limit
> > >> +Date: Nov 2018
> > >> +Contact: linux...@vger.kernel.org
> > >> +Description:
> > >> + This entry configures the incoming VBUS voltage limit
> > >> currently
> > >> + set in the supply. Normally this is configured based on
> > >> + system-level knowledge or user input (e.g. This is part of
> > >> the
> > >> + Pixel C's thermal management strategy to effectively limit
> > >> the
> > >> + input power to 5V when the screen is on to meet Google's
> > >> skin
> > >> + temperature targets). Note that this feature should not be
> > >> + used for safety critical things.
--
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http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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