linux-kernel - Re: [PATCH v4 3/6] dt-bindings: power: tegra: Add binding for core power domain

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Message-ID: <80410199-3b5f-13b7-25b7-3fbd009c31e7@gmail.com>
Date:   Thu, 25 Mar 2021 20:38:16 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Rob Herring <robh@...nel.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mark Brown <broonie@...nel.org>,
        Paul Fertser <fercerpav@...il.com>,
        Matt Merhar <mattmerhar@...tonmail.com>,
        Peter Geis <pgwipeout@...il.com>,
        Nicolas Chauvet <kwizart@...il.com>,
        Viresh Kumar <vireshk@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        devicetree@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/6] dt-bindings: power: tegra: Add binding for core
 power domain

25.03.2021 17:49, Thierry Reding пишет:
> On Wed, Mar 24, 2021 at 02:01:29AM +0300, Dmitry Osipenko wrote:
>> 24.03.2021 01:48, Rob Herring пишет:
>>> On Sun, Mar 14, 2021 at 07:48:07PM +0300, Dmitry Osipenko wrote:
>>>> All NVIDIA Tegra SoCs have a core power domain where majority of hardware
>>>> blocks reside. Add binding for the core power domain.
>>>>
>>>> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
>>>> ---
>>>>  .../power/nvidia,tegra20-core-domain.yaml     | 51 +++++++++++++++++++
>>>>  1 file changed, 51 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/power/nvidia,tegra20-core-domain.yaml
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/power/nvidia,tegra20-core-domain.yaml b/Documentation/devicetree/bindings/power/nvidia,tegra20-core-domain.yaml
>>>> new file mode 100644
>>>> index 000000000000..4692489d780a
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/power/nvidia,tegra20-core-domain.yaml
>>>> @@ -0,0 +1,51 @@
>>>> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
>>>> +%YAML 1.2
>>>> +---
>>>> +$id: http://devicetree.org/schemas/power/nvidia,tegra20-core-domain.yaml#
>>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>>> +
>>>> +title: NVIDIA Tegra Core Power Domain
>>>> +
>>>> +maintainers:
>>>> +  - Dmitry Osipenko <digetx@...il.com>
>>>> +  - Jon Hunter <jonathanh@...dia.com>
>>>> +  - Thierry Reding <thierry.reding@...il.com>
>>>> +
>>>> +allOf:
>>>> +  - $ref: power-domain.yaml#
>>>> +
>>>> +properties:
>>>> +  compatible:
>>>> +    enum:
>>>> +      - nvidia,tegra20-core-domain
>>>> +      - nvidia,tegra30-core-domain
>>>> +
>>>> +  operating-points-v2:
>>>> +    description:
>>>> +      Should contain level, voltages and opp-supported-hw property.
>>>> +      The supported-hw is a bitfield indicating SoC speedo or process
>>>> +      ID mask.
>>>> +
>>>> +  "#power-domain-cells":
>>>> +    const: 0
>>>> +
>>>> +  power-supply:
>>>> +    description:
>>>> +      Phandle to voltage regulator connected to the SoC Core power rail.
>>>> +
>>>> +required:
>>>> +  - compatible
>>>> +  - operating-points-v2
>>>> +  - "#power-domain-cells"
>>>> +  - power-supply
>>>> +
>>>> +additionalProperties: false
>>>> +
>>>> +examples:
>>>> +  - |
>>>> +    power-domain {
>>>> +        compatible = "nvidia,tegra20-core-domain";
>>>> +        operating-points-v2 = <&opp_table>;
>>>> +        power-supply = <&regulator>;
>>>> +        #power-domain-cells = <0>;
>>>
>>> AFAICT, there's no way to access this 'hardware'?
>> correct
> 
> To avoid exposing this "virtual" device in device tree, could this
> instead be modelled as a child node of the PMC node? We already expose a
> couple of generic power domains that way on Tegra210 and later, so
> perhaps some of that infrastructure can be reused? I suppose given that
> this is different from the standard powergate domains that we expose so
> far, this may need a different implementation, but from a device tree
> bindings point of view it could fit in with that.

At a quick glance this should be too troublesome because OPP and regulator frameworks require a proper/real backing device.

Perhaps we could either turn the whole PMC into a core-domain or add a virtual device as a child of PMC, like this:

diff --git a/arch/arm/boot/dts/tegra20.dtsi b/arch/arm/boot/dts/tegra20.dtsi
index 79364cdafeab..717273048caf 100644
--- a/arch/arm/boot/dts/tegra20.dtsi
+++ b/arch/arm/boot/dts/tegra20.dtsi
@@ -850,6 +850,12 @@ pd_mpe: mpe {
 				#power-domain-cells = <0>;
 			};
 		};
+
+		pd_core: core-domain {
+			compatible = "nvidia,tegra20-core-domain";
+			operating-points-v2 = <&core_opp_table>;
+			#power-domain-cells = <0>;
+		};
 	};
 
 	mc: memory-controller@...0f000 {

but then this is still a virtual device, although in a bit nicer way.

It feels like yours suggestion might result in a hardware description that is closer to reality since PMC controls fan out of all power rails within SoC.