[v6,0/6] Introduce Power domain based warming device driver

Certain resources modeled as a generic power domain in linux kernel can be
used to warm up the SoC (mx power domain on sdm845) if the temperature
falls below certain threshold. These power domains can be considered as
thermal warming devices.  (opposite of thermal cooling devices).

In kernel, these warming devices can be modeled as a thermal cooling
device. Since linux kernel today has no instance of a resource modeled as
a power domain acting as a thermal warming device, a generic power domain
based thermal warming device driver that can be used pan-Socs is the
approach taken in this patch series. Since thermal warming devices can be
thought of as the mirror opposite of thermal cooling devices, this patch
series re-uses thermal cooling device framework. To use these power
domains as warming devices require further tweaks in the thermal framework
which are out of scope of this patch series. These tweaks have been posted
as a separate series[1].

The first patch in this series extends the genpd framework to export out
the performance states of a power domain so that when a power domain is
modeled as a cooling device, the number of possible states and current
state of the cooling device can be retrieved from the genpd framework.

The second patch implements the newly added genpd callback for Qualcomm
RPMH power domain driver which hosts the mx power domain.

The third patch introduces a new cooling device register API that allows
a parent to be specified for the cooling device.

The fourth patch introduces the generic power domain warming device
driver.

The fifth patch extends Qualcomm RPMh power controller driver to register
mx power domain as a thermal warming device in the kernel.

The sixth patch describes the dt binding extensions for mx power domain to
be a thermal warming device.

The seventh patch introduces the DT entreis for sdm845 to register mx
power domain as a thermal warming device.

v1->v2:
	- Rename the patch series from "qcom: Model RPMH power domains as
	  thermal cooling devices" to "Introduce Power domain based
	  thermal warming devices" as it is more appropriate.
	- Introduce a new patch(patch 3) describing the dt-bindings for
	  generic power domain warming device.
	- Patch specific changes mentioned in respective patches.

v2->v3:
	- Changed power domain warming device from a virtual device node
	  entry in DT to being a subnode of power domain controller
	  binding following Rob's review comments.
	- Implemented Ulf's review comments.
	- The changes above introduced two new patches (patch 3 and 4)
v3->v4:
	- Dropped late_init hook in cooling device ops. Instead introduced
	  a new cooling device register API that allows to define a parent
	  for the cooling device.
	- Patch specific changes mentioned in respective patches. 

v4->v5:
	- Dropped the patch that introduced the cooling device register
	  API with parent as per review comments from Ulf. 
	- Patch specific changes mentioned in respective patches.

v5->v6:
	- Rebased to latest kernel
	- Few other fixes identified in the review process mentioned in
	  respective patches

1. https://lkml.org/lkml/2019/9/18/1180

Thara Gopinath (6):
  PM/Domains: Add support for retrieving genpd performance states
    information
  soc: qcom: rpmhpd: Introduce function to retrieve power domain
    performance state count
  thermal: Add generic power domain warming device driver.
  soc: qcom: Extend RPMh power controller driver to register warming
    devices.
  dt-bindings: power: Extend RPMh power controller binding to describe
    thermal warming device
  arm64: dts: qcom: Indicate rpmhpd hosts a power domain that can be
    used as a warming device.

 .../devicetree/bindings/power/qcom,rpmpd.yaml |   3 +
 arch/arm64/boot/dts/qcom/sdm845.dtsi          |   1 +
 drivers/base/power/domain.c                   |  37 ++++
 drivers/soc/qcom/rpmhpd.c                     |  25 ++-
 drivers/thermal/Kconfig                       |  10 ++
 drivers/thermal/Makefile                      |   4 +
 drivers/thermal/pd_warming.c                  | 169 ++++++++++++++++++
 include/linux/pd_warming.h                    |  29 +++
 include/linux/pm_domain.h                     |  13 ++
 9 files changed, 290 insertions(+), 1 deletion(-)
 create mode 100644 drivers/thermal/pd_warming.c
 create mode 100644 include/linux/pd_warming.h

On Thu, 4 Jun 2020 at 03:53, Thara Gopinath <thara.gopinath@linaro.org> wrote:
>
> RPMh power controller hosts mx domain that can be used as thermal warming
> device. Add #cooling-cells property to the power domain provider node to
> indicate this.
>
> Signed-off-by: Thara Gopinath <thara.gopinath@linaro.org>
> Acked-by: Rob Herring <robh@kernel.org>

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>

Kind regards
Uffe


> ---
>
> v3->v4:
>         - Removed subnode to indicate that mx power domain is a warming
>           device. Instead #cooling-cells is used as a power domain
>           provider property to indicate if the provider hosts a power
>           domain that can be used as a warming device.
>
> v4->v5:
>         Moved the property from .txt format to .yaml format.
>
>  Documentation/devicetree/bindings/power/qcom,rpmpd.yaml | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/power/qcom,rpmpd.yaml b/Documentation/devicetree/bindings/power/qcom,rpmpd.yaml
> index 8058955fb3b9..a4fbbd88ce18 100644
> --- a/Documentation/devicetree/bindings/power/qcom,rpmpd.yaml
> +++ b/Documentation/devicetree/bindings/power/qcom,rpmpd.yaml
> @@ -28,6 +28,9 @@ properties:
>    '#power-domain-cells':
>      const: 1
>
> +  '#cooling-cells':
> +    const: 2
> +
>    operating-points-v2: true
>
>    opp-table:
> --
> 2.20.1
>

Hi!

> >>falls below certain threshold. These power domains can be considered as
> >>thermal warming devices.  (opposite of thermal cooling devices).
> >
> >Would you explain when this is needed?
> >
> >I'd normally expect "too low" temperature to be a problem during power-on, but at
> >that time Linux is not running so it can not provide the heating...
> Hi Pavel,
> 
> This is more in the scenario if the system in on and temperature is dipping
> (I have been told in colder climates). Idea is to turn on resources so as to
> prevent further dipping of temperature if possible.

I guess even that makes sense...

But, out of curiosity, do you know which kind of device is that and in what
kind of environment? I mean, theoretically it may make sense on a cellphone,
but... I guess you have some fun device and would like to know what it is :-).

Hmm. And we can make this quite generic.

while (too_cold())
	barrier();

Wasting power is really easy :-).
									Pavel