Re: [PATCH 0/2] thermal, OPP: move the CPU power estimation to the OPP library

[Eduardo Valentin <edubezval@gmail.com>]

On Tue, Jan 09, 2018 at 11:02:50AM +0000, Quentin Perret wrote:
> Currently, IPA estimates the power dissipated by a CPU at each available OPP
> using its capacitance (the dynamic-power-coefficient DT binding). This series
> relocates this feature into the OPP library as a preparation for future
> changes. More specifically:
> 
>    1. The current DT-based approach for power estimation will need deep
>       changes to support SCMI-provided power values. While the thermal
>       subsystem is not necessarily the best place to hide multiple power
>       estimation methods, the OPP library appears to be a good candidate to
>       implement the required platform abstraction.
>    2. The energy models of CPUs will be needed by other clients in the future
>       (such as the task scheduler or CPUFreq governors for example) in order
>       to make energy-aware decisions. The relocation to the OPP library will
>       enable code re-use and all clients will benefit form the platform
>       abstraction mentioned previously.

To be quite frank, I am happy to see this leaving thermal subsystem.
However, a few concerns with the patch set as it is. First, I am not
convinced PM OPP is the right place to put this, nor I see a good
explanation put in the patch set why it must be part of PM OPP.
Second, looks like we are following ARM "good" practice of fixing
problems of the future. I would only really sign off for this series
when we see real "other future users", otherwise we end up with the
infamous static power scenario in 2-3 years down the row. If we
currently do not have users of this IN MAINLINE KERNEL, then the series
is not for upstream.

> 
> Quentin Perret (2):
>   PM / OPP: introduce an OPP power estimation helper
>   thermal: cpu_cooling: use power models from the OPP library
> 
>  drivers/cpufreq/arm_big_little.c   |  2 ++
>  drivers/cpufreq/cpufreq-dt.c       |  2 ++
>  drivers/cpufreq/mediatek-cpufreq.c |  2 ++
>  drivers/opp/core.c                 | 40 +++++++++++++++++++++++++
>  drivers/opp/of.c                   | 61 ++++++++++++++++++++++++++++++++++++++
>  drivers/opp/opp.h                  |  4 +++
>  drivers/thermal/cpu_cooling.c      | 33 ++++++---------------
>  include/linux/pm_opp.h             | 20 +++++++++++++
>  8 files changed, 140 insertions(+), 24 deletions(-)
> 
> -- 
> 2.15.1
>