Re: [PATCH] arm64: dts: qcom: Clean up sc7180-trogdor voltage rails

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Mon 11 Jan 15:48 CST 2021, Doug Anderson wrote:

> Hi Bjorn,
> 
> On Mon, Dec 7, 2020 at 2:33 PM Douglas Anderson <dianders@chromium.org> wrote:
> >
> > For a bunch of rails we really don't do anything with them in Linux.
> > These are things like modem voltage rails that the modem manages these
> > itself and core rails (like IO rails) that are setup to just
> > automagically do the right thing by the firmware.
> >
> > Let's stop even listing those rails in our device tree.
> >
> > The net result of this is that some of these rails might be able to go
> > down to a lower voltage or perhaps transition to LPM (low power mode)
> > sometimes.
> >
> > Here's a list of what we're doing and why:
> >
> > * L1A - only goes to SoC and doesn't seem associated with any
> >   particular peripheral. Kernel isn't doing anything with
> >   this. Removing from dts. NET IMPACT: rail might drop from 1.2V to
> >   1.178V and switch to LPM in some cases depending on firmware.
> > * L2A - only goes to SoC and doesn't seem associated with any
> >   particular peripheral. Kernel isn't doing anything with
> >   this. Removing from dts. NET IMPACT: rail might switch to LPM in
> >   some cases depending on firmware.
> > * L3A - only goes to SoC and doesn't seem associated with any
> >   particular peripheral. Kernel isn't doing anything with
> >   this. Removing from dts. NET IMPACT: rail might switch to LPM in
> >   some cases depending on firmware.
> > * L5A - seems to be totally unused as far as I can tell and doesn't
> >   even come off QSIP. Removing from dts.
> > * L6A - only goes to SoC and doesn't seem associated with any
> >   particular peripheral (I think?). Kernel isn't doing anything with
> >   this. Removing from dts. NET IMPACT: rail might switch to LPM in
> >   some cases depending on firmware.
> > * L16A - Looks like this is only used for internal RF stuff. Removing
> >   from dts. NET IMPACT: rail might switch to LPM in some cases
> >   depending on firmware.
> > * L1C - Just goes to WiFi / Bluetooth. Trust how IDP has this set and
> >   put this back at 1.616V min.
> > * L4C - This goes out to the eSIM among other places. This looks like
> >   it's intended to be for SIM card and modem manages. NET IMPACT:
> >   rail might switch to LPM in some cases depending on firmware.
> > * L5C - This goes to the physical SIM.  This looks like it's intended
> >   to be for SIM card and modem manages. NET IMPACT: rail might drop
> >   from 1.8V to 1.648V and switch to LPM in some cases depending on
> >   firmware.
> >
> > NOTE: in general for anything which is supposed to be managed by Linux
> > I still left it all forced to HPM since I'm not 100% sure that all the
> > needed calls to regulator_set_load() are in place and HPM is safer.
> > Switching more things to LPM can happen in a future patch.
> >
> > ALSO NOTE: Power measurements showed no measurable difference after
> > applying this patch, so perhaps it should be viewed more as a cleanup
> > than any power savings.
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > ---
> >
> >  arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi | 82 ++------------------
> >  1 file changed, 7 insertions(+), 75 deletions(-)
> 
> We've been running with this in the downstream tree since December 8th
> and nobody has yelled.  You can see <https://crrev.com/c/2573506>.  Is
> it a good time for it to land upstream?
> 

Sure thing, I will pick it up. Thanks for the ping!

Regards,
Bjorn