[Intel-gfx] [PATCH 3/4] drm/i915/hwmon: Add HWMON power sensor support

[Dixit, Ashutosh]

On Mon, 20 Jun 2022 13:58:49 -0700, Guenter Roeck wrote:
>

Hi Guenter, Thanks for taking a look.

> > diff --git a/Documentation/ABI/testing/sysfs-driver-intel-i915-hwmon b/Documentation/ABI/testing/sysfs-driver-intel-i915-hwmon
> > index 24c4b7477d51..945f472dd4a2 100644
> > --- a/Documentation/ABI/testing/sysfs-driver-intel-i915-hwmon
> > +++ b/Documentation/ABI/testing/sysfs-driver-intel-i915-hwmon
> > @@ -5,3 +5,23 @@ Contact:	dri-devel at lists.freedesktop.org
> >   Description:	RO. Current Voltage in millivolt.
> >			Only supported for particular Intel i915 graphics
> > platforms.
> > +
> > +What:		/sys/devices/.../hwmon/hwmon<i>/power1_max
> > +Date:		June 2022
> > +KernelVersion:	5.19
> > +Contact:	dri-devel at lists.freedesktop.org
> > +Description:	RW. Card reactive sustained  (PL1/Tau) power limit in microwatts.
> > +
> > +		The power controller will throttle the operating frequency
> > +		if the power averaged over a window (typically seconds)
> > +		exceeds this limit.
> > +
> > +		Only supported for particular Intel i915 graphics platforms.
> > +
> > +What:		/sys/devices/.../hwmon/hwmon<i>/power1_max_default
>
> I don't immediately see the reason for not using the standard power1_cap
> attribute, which is described as
>
>		If power use rises above this limit, the
>                 system should take action to reduce power use.
>
> and pretty much matches the description above.

Sorry I believe you are referring to the description above which is for the
standard power1_max attribute (as we have used it). The non-standard
attribute is power1_max_default the description for which is below ("Card
default power limit (default TDP setting)").

> > +Date:		June 2022
> > +KernelVersion:	5.19
> > +Contact:	dri-devel at lists.freedesktop.org
> > +Description:	RO. Card default power limit (default TDP setting).

Actually we do not want to use custom hwmon attributes as far as
possible and are looking for some guidance on which standard attributes
which we should use instead.

These are the power attributes we are interested in: the two above and
another one which will come in a future patch:

1. PL1 (RW)

   https://www.hardwaretimes.com/intel-10th-gen-cpu-power-consumption-explained-pl1-pl2-and-tau/

2. TDP (RO)

   https://en.wikipedia.org/wiki/Thermal_design_power

3. Tau (RW)

   https://www.hardwaretimes.com/intel-10th-gen-cpu-power-consumption-explained-pl1-pl2-and-tau/

Would you be able to suggest if there are standard hwmon attributes which
we would be able to use for these three? We also want to use the read/write
permissions as shown above.

Thanks.
--
Ashutosh