Re: [PATCH] dt: psci: Update DT bindings to support hierarchical PSCI states

[Rob Herring]

On Fri, Dec 22, 2017 at 03:32:07PM +0100, Ulf Hansson wrote:
> From: Lina Iyer <lina.iyer@xxxxxxxxxx>
> 
> Update DT bindings to represent hierarchical CPU and CPU domain idle states
> for PSCI. Also update the PSCI examples to clearly show how flattened and
> hierarchical idle states can be represented in DT.
> 
> Signed-off-by: Lina Iyer <lina.iyer@xxxxxxxxxx>
> Signed-off-by: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> ---
> 
> For your information, I have picked up the work from Lina Iyer around the so
> called CPU cluster idling series [1,2] and I working on new versions. However,
> I decided to post the updates to the PSCI DT bindings first, as they will be
> needed to be agreed upon before further changes can be done to the PSCI firmware
> driver.
> 
> Note, these bindings have been discussed over and over again, at LKML, but
> especially also at various Linux conferences, like LPC and Linaro Connect. We
> finally came to a conclusion and the changes we agreed upon, should be reflected
> in this update.
> 
> Of course, it's a while ago since the latest discussions, but hopefully people
> don't have too hard time to remember.

Vaguely...

> 
> Kind regards
> Uffe
> 
> [1]
> https://www.spinics.net/lists/arm-kernel/msg566200.html
> 
> [2]
> https://lwn.net/Articles/716300/
> 
> ---
>  Documentation/devicetree/bindings/arm/psci.txt | 152 +++++++++++++++++++++++++
>  1 file changed, 152 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/arm/psci.txt b/Documentation/devicetree/bindings/arm/psci.txt
> index a2c4f1d..5a8f11b 100644
> --- a/Documentation/devicetree/bindings/arm/psci.txt
> +++ b/Documentation/devicetree/bindings/arm/psci.txt
> @@ -105,7 +105,159 @@ Case 3: PSCI v0.2 and PSCI v0.1.
>  		...
>  	};
>  
> +PSCI v1.0 onwards, supports OS-Initiated mode for powering off CPUs and CPU
> +clusters from the firmware. For such topologies the PSCI firmware driver acts
> +as pseudo-controller, which may be specified in the psci DT node. The
> +definitions of the CPU and the CPU cluster topology, must conform to the domain
> +idle state specification [3]. The domain idle states themselves, must be
> +compatible with the defined 'domain-idle-state' binding [1], and also need to
> +specify the arm,psci-suspend-param property for each idle state.
> +
> +DT allows representing CPU and CPU cluster idle states in two different ways -
> +
> +The flattened model as given in Example 1, lists CPU's idle states followed by
> +the domain idle state that the CPUs may choose. This is the general practice
> +followed in PSCI firmwares that support Platform Coordinated mode. Note that
> +the idle states are all compatible with "arm,idle-state".
> +
> +Example 2 represents the hierarchical model of CPU and domain idle states.
> +CPUs define their domain provider in their DT node. The domain controls the
> +power to the CPU and possibly other h/w blocks that would be powered off when
> +the CPU is powered off. The CPU's idle states may therefore be considered as
> +the domain's idle states and have the compatible "arm,idle-state". Such domains
> +may be embedded within another domain that represents common h/w blocks between
> +these CPUs viz. the cluster. The idle states of the cluster would be
> +represented as the domain's idle states. In order to use OS-Initiated mode of
> +PSCI in the firmware, the hierarchical representation must be used.
> +
> +Example 1: Flattened representation of CPU and domain idle states
> +	cpus {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		CPU0: cpu@0 {
> +			device_type = "cpu";
> +			compatible = "arm,cortex-a53", "arm,armv8";
> +			reg = <0x0>;
> +			enable-method = "psci";
> +			cpu-idle-states = <&CPU_PWRDN>, <&CLUSTER_RET>,
> +					  <&CLUSTER_PWR_DWN>;
> +		};
> +
> +		CPU1: cpu@1 {
> +			device_type = "cpu";
> +			compatible = "arm,cortex-a57", "arm,armv8";
> +			reg = <0x100>;
> +			enable-method = "psci";
> +			cpu-idle-states = <&CPU_PWRDN>, <&CLUSTER_RET>,
> +					  <&CLUSTER_PWR_DWN>;
> +		};
> +
> +		idle-states {
> +			CPU_PWRDN: cpu_power_down{

Use '-' rather than '_'. dtc has more warnings since last time...

> +				compatible = "arm,idle-state";
> +				arm,psci-suspend-param = <0x000001>;
> +				entry-latency-us = <10>;
> +				exit-latency-us = <10>;
> +				min-residency-us = <100>;
> +			};
> +
> +			CLUSTER_RET: domain_ret {
> +				compatible = "arm,idle-state";
> +				arm,psci-suspend-param = <0x1000010>;
> +				entry-latency-us = <500>;
> +				exit-latency-us = <500>;
> +				min-residency-us = <2000>;
> +			};
> +
> +			CLUSTER_PWR_DWN: domain_off {
> +				compatible = "arm,idle-state";
> +				arm,psci-suspend-param = <0x1000030>;
> +				entry-latency-us = <2000>;
> +				exit-latency-us = <2000>;
> +				min-residency-us = <6000>;
> +			};
> +	};
> +
> +	psci {
> +		compatible = "arm,psci-0.2";
> +		method = "smc";
> +	};
> +
> +Example 2: Hierarchical representation of CPU and domain idle states
> +
> +	cpus {
> +		#address-cells = <1>;
> +		#size-cells = <0>;
> +
> +		CPU0: cpu@0 {
> +			device_type = "cpu";
> +			compatible = "arm,cortex-a53", "arm,armv8";
> +			reg = <0x0>;
> +			enable-method = "psci";
> +			power-domains = <&CPU_PD0>;
> +		};
> +
> +		CPU1: cpu@1 {
> +			device_type = "cpu";
> +			compatible = "arm,cortex-a57", "arm,armv8";
> +			reg = <0x100>;
> +			enable-method = "psci";
> +			power-domains = <&CPU_PD1>;
> +		};
> +
> +		idle-states {
> +			CPU_PWRDN: cpu_power_down{
> +				compatible = "arm,idle-state";
> +				arm,psci-suspend-param = <0x000001>;
> +				entry-latency-us = <10>;
> +				exit-latency-us = <10>;
> +				min-residency-us = <100>;
> +			};
> +
> +			CLUSTER_RET: domain_ret {
> +				compatible = "domain-idle-state";
> +				arm,psci-suspend-param = <0x1000010>;
> +				entry-latency-us = <500>;
> +				exit-latency-us = <500>;
> +				min-residency-us = <2000>;
> +			};
> +
> +			CLUSTER_PWR_DWN: domain_off {
> +				compatible = "domain-idle-state";
> +				arm,psci-suspend-param = <0x1000030>;
> +				entry-latency-us = <2000>;
> +				exit-latency-us = <2000>;
> +				min-residency-us = <6000>;
> +			};
> +		};
> +	};
> +
> +	psci {
> +		compatible = "arm,psci-1.0";
> +		method = "smc";
> +
> +		CPU_PD0: cpu-pd@0 {

A unit address without reg property is now a warning.

> +			#power-domain-cells = <0>;
> +			domain-idle-states = <&CPU_PWRDN>;
> +			power-domains = <&CLUSTER_PD>;
> +		};
> +
> +		CPU_PD1: cpu-pd@1 {
> +			#power-domain-cells = <0>;
> +			domain-idle-states =  <&CPU_PWRDN>;
> +			power-domains = <&CLUSTER_PD>;

Could this node be a child of CLUSTER_PD rather than having a phandle? 
Doesn't matter so much here, but when you have 3 levels?

> +		};

These 2 nodes are identical, so why do you need both?

> +
> +		CLUSTER_PD: cluster-pd@0 {
> +			#power-domain-cells = <0>;
> +			domain-idle-states = <&CLUSTER_RET>, <&CLUSTER_PWR_DWN>;
> +		};
> +	};
> +
>  [1] Kernel documentation - ARM idle states bindings
>      Documentation/devicetree/bindings/arm/idle-states.txt
>  [2] Power State Coordination Interface (PSCI) specification
>      http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf
> +[3]. PM Domains description
> +    Documentation/devicetree/bindings/power/power_domain.txt
> -- 
> 2.7.4
>