Re: [PATCH v2 3/3] dt-bindings: thermal: update sustainable-power with abstract scale

[Lukasz Luba]

Hi Doug,

On 10/2/20 4:47 PM, Doug Anderson wrote:
> Hi,
>
> On Fri, Oct 2, 2020 at 8:13 AM Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> > Hi Doug,
> >
> > On 10/2/20 3:31 PM, Doug Anderson wrote:
> > > Hi,
> > >
> > > On Fri, Oct 2, 2020 at 4:45 AM Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> > > > Update the documentation for the binding 'sustainable-power' and allow
> > > > to provide values in an abstract scale. It is required when the cooling
> > > > devices use an abstract scale for their power values.
> > > >
> > > > Signed-off-by: Lukasz Luba <lukasz.luba@xxxxxxx>
> > > > ---
> > > >    .../devicetree/bindings/thermal/thermal-zones.yaml  | 13 +++++++++----
> > > >    1 file changed, 9 insertions(+), 4 deletions(-)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/thermal/thermal-zones.yaml b/Documentation/devicetree/bindings/thermal/thermal-zones.yaml
> > > > index 3ec9cc87ec50..4d8f2e37d1e6 100644
> > > > --- a/Documentation/devicetree/bindings/thermal/thermal-zones.yaml
> > > > +++ b/Documentation/devicetree/bindings/thermal/thermal-zones.yaml
> > > > @@ -99,10 +99,15 @@ patternProperties:
> > > >          sustainable-power:
> > > >            $ref: /schemas/types.yaml#/definitions/uint32
> > > >            description:
> > > > -          An estimate of the sustainable power (in mW) that this thermal zone
> > > > -          can dissipate at the desired control temperature. For reference, the
> > > > -          sustainable power of a 4-inch phone is typically 2000mW, while on a
> > > > -          10-inch tablet is around 4500mW.
> > > > +          An estimate of the sustainable power (in mW or in an abstract scale)
> > > > +         that this thermal zone can dissipate at the desired control
> > > > +         temperature. For reference, the sustainable power of a 4-inch phone
> > > > +         is typically 2000mW, while on a 10-inch tablet is around 4500mW.
> > > > +
> > > > +         It is possible to express the sustainable power in an abstract
> > > > +         scale. This is the case when the related cooling devices use also
> > > > +         abstract scale to express their power usage. The scale must be
> > > > +         consistent.
> > >
> > > Two thoughts:
> > >
> > > 1. If we're going to allow "sustainable-power" to be in abstract
> > > scale, why not allow "dynamic-power-coefficient" to be in abstract
> > > scale too?  I assume that the whole reason against that originally was
> > > the idea of device tree purity, but if we're allowing the abstract
> > > scale here then there seems no reason not to allow it for
> > > "dynamic-power-coefficient".
> >
> > With this binding it's a bit more tricky.
> > I also have to discuss a few things internally. This requirement of
> > uW/MHz/V^2 makes the code easier also for potential drivers
> > like GPU (which are going to register the devfreq cooling with EM).
> >
> > Let me think about it, but for now I would just update these bits.
> > These are required to proper IPA operation, the dyn.-pow.-coef. is a
> > nice to have and possible next step.
>
> I guess the problem is that Rajendra is currently planning to remove
> all the "dynamic-power-coefficient" values from device tree right now
> and move them to the source code because the numbers we currently have
> in the device tree _are_ in abstract scale and thus violate the
> bindings.  Moving this to source code won't help us get to more real
> power numbers (since it'll still be abstract scale), it'll just be
> pure churn.  If we're OK with the abstract scale in general then we
> should allow it everywhere and not add churn for no reason.

I just want to notify you that I had internal conversation about this
'dynamic-power-coefficient' binding and abstract scale. We would
change it as well, similarly to 'sustainable-power'. It must pass
internal review and I will send the v3 of this series.

Regards,
Lukasz