[RESEND,6/8] Documentation: EM: Add artificial EM registration description

Add description about new artificial EM registration and use cases.
Update also the documentation with the new .get_cost() callback
description and usage.

Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
---
 Documentation/power/energy-model.rst | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

Thanks for documenting this as well.

On Monday 21 Mar 2022 at 09:57:27 (+0000), Lukasz Luba wrote:
> Add description about new artificial EM registration and use cases.
> Update also the documentation with the new .get_cost() callback
> description and usage.
> 
> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
> ---
>  Documentation/power/energy-model.rst | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/Documentation/power/energy-model.rst b/Documentation/power/energy-model.rst
> index fd29ed2506c0..feb257b7f350 100644
> --- a/Documentation/power/energy-model.rst
> +++ b/Documentation/power/energy-model.rst
> @@ -123,6 +123,26 @@ allows a platform to register EM power values which are reflecting total power
>  (static + dynamic). These power values might be coming directly from
>  experiments and measurements.
>  
> +Registration of 'artificial' EM
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> +
> +There is an option to provide a custom callback for drivers missing detailed
> +knowledge about power value for each performance state. The callback
> +.get_cost() is optional and provides the 'cost' values used by the EAS.
> +This is useful for platforms that only provide information on relative
> +efficiency between CPU types, where one could use the information to
> +create an abstract power model. But even an abstract power model can
> +sometimes be hard to fit in, given the input power value size restrictions.
> +The .get_cost() allows to provide the 'cost' values which reflect the
> +efficiency of the CPUs. This would allow to provide EAS information which
> +has different relation than what would be forced by the EM internal
> +formulas calculating 'cost' values. To register an EM for such platform, the
> +driver must set the flag 'milliwatts' to 0, provide .get_power() callback
> +and provide .get_cost() callback. The EM framework would handle such platform

Maybe it worth adding a note here that the power values provided with
.get_power() are only for information purposes and that they don't have
any functional use.

> +properly during registration. A flag EM_PERF_DOMAIN_ARTIFICIAL is set for such
> +platform. Special care should be taken by other frameworks which are using EM
> +to test and treat this flag properly.
> +
>  Registration of 'simple' EM
>  ~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  

Reviewed-by: Ionela Voinescu <ionela.voinescu@arm.com>

> -- 
> 2.17.1
>