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Date:   Fri, 19 Jul 2019 12:29:56 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To:     Ulf Hansson <ulf.hansson@linaro.org>
Cc:     Sudeep Holla <sudeep.holla@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        "Raju P . L . S . S . S . N" <rplsssn@codeaurora.org>,
        Amit Kucheria <amit.kucheria@linaro.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Stephen Boyd <sboyd@kernel.org>,
        Niklas Cassel <niklas.cassel@linaro.org>,
        Tony Lindgren <tony@atomide.com>,
        Kevin Hilman <khilman@kernel.org>,
        Lina Iyer <ilina@codeaurora.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Souvik Chakravarty <souvik.chakravarty@arm.com>,
        linux-pm@vger.kernel.org, linux-arm-msm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Lina Iyer <lina.iyer@linaro.org>
Subject: Re: [PATCH 01/18] dt: psci: Update DT bindings to support
 hierarchical PSCI states
Message-ID: <20190719112947.GA22746@e121166-lin.cambridge.arm.com>
References: <20190513192300.653-1-ulf.hansson@linaro.org>
 <20190513192300.653-2-ulf.hansson@linaro.org>
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On Mon, May 13, 2019 at 09:22:43PM +0200, Ulf Hansson wrote:
> From: Lina Iyer <lina.iyer@linaro.org>
> 
> Update DT bindings to represent hierarchical CPU and CPU PM 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@linaro.org>
> Reviewed-by: Rob Herring <robh@kernel.org>
> Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
> Co-developed-by: Ulf Hansson <ulf.hansson@linaro.org>
> Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
> ---
> 
> Changes:
> 	- None.
> 
> ---
>  .../devicetree/bindings/arm/psci.txt          | 166 ++++++++++++++++++
>  1 file changed, 166 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/arm/psci.txt b/Documentation/devicetree/bindings/arm/psci.txt
> index a2c4f1d52492..e6d3553c8df8 100644
> --- a/Documentation/devicetree/bindings/arm/psci.txt
> +++ b/Documentation/devicetree/bindings/arm/psci.txt
> @@ -105,7 +105,173 @@ Case 3: PSCI v0.2 and PSCI v0.1.
>  		...
>  	};
>  
> +ARM systems can have multiple cores sometimes in hierarchical arrangement.
> +This often, but not always, maps directly to the processor power topology of
> +the system. Individual nodes in a topology have their own specific power states
> +and can be better represented in DT hierarchically.
> +
> +For these cases, the definitions of the idle states for the CPUs and the CPU
> +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 CPUs and CPU 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. Note that the idle states are
> +all compatible with "arm,idle-state". Additionally, for the domain idle state
> +the "arm,psci-suspend-param" represents a superset of the CPU's idle state.
> +
> +Example 2 represents the hierarchical model of CPUs and domain idle states.
> +CPUs define their domain provider in their psci DT node. The domain controls
> +the power to the CPU and possibly other h/w blocks that would enter an idle
> +state along with the CPU. 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 also be embedded within another domain that may represent common h/w blocks
> +between these CPUs. The idle states of the CPU topology shall be represented as
> +the domain's idle states. Note that for the domain idle state, the
> +"arm,psci-suspend-param" represents idle states hierarchically.
> +
> +In PSCI firmware v1.0, the OS-Initiated mode is introduced. However, the
> +flattened vs hierarchical DT representation is orthogonal to the OS-Initiated
> +vs the platform-coordinated PSCI CPU suspend modes, thus should be considered
> +independent of each other.
> +
> +The hierarchical representation helps and makes it easy to implement OSI mode
> +and OS implementations may choose to mandate it. For the default platform-
> +coordinated mode, both representations are viable options.
> +
> +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_PWRDN>;
> +		};
> +
> +		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_PWRDN>;
> +		};
> +
> +		idle-states {
> +			CPU_PWRDN: cpu-power-down {
> +				compatible = "arm,idle-state";
> +				arm,psci-suspend-param = <0x0000001>;

This value is wrong, StateType must be 1 for CPU power down states.

> +				entry-latency-us = <10>;
> +				exit-latency-us = <10>;
> +				min-residency-us = <100>;
> +			};
> +
> +			CLUSTER_RET: cluster-retention {
> +				compatible = "arm,idle-state";
> +				arm,psci-suspend-param = <0x1000011>;

It must be made crystal clear that this is the *full* power_state
that is passed to the CPU_SUSPEND call. It is already specified
in the bindings.

As Sudeep pointed out already, OR'ing the power_state parameters values
across power domains is wrong, in that there is nothing in the PSCI
specifications that enforces a power_state parameter scheme whereby
different "levels" are assigned different bitfields, in particular with
the extended format a power_state parameter for eg "system" level is not
necessarily OR'ed value of cluster|cpu|system values.

So, to sum it up, arm,psci-suspend-param must be the full power_state
parameter to be passed to CPU_SUSPEND and must be specified in full for
every CPU and power domain idle state.

Thanks,
Lorenzo

> +				entry-latency-us = <500>;
> +				exit-latency-us = <500>;
> +				min-residency-us = <2000>;
> +			};
> +
> +			CLUSTER_PWRDN: cluster-power-down {
> +				compatible = "arm,idle-state";
> +				arm,psci-suspend-param = <0x1000031>;
> +				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>;
> +			power-domain-names = "psci";
> +		};
> +
> +		CPU1: cpu@1 {
> +			device_type = "cpu";
> +			compatible = "arm,cortex-a57", "arm,armv8";
> +			reg = <0x100>;
> +			enable-method = "psci";
> +			power-domains = <&CPU_PD1>;
> +			power-domain-names = "psci";
> +		};
> +
> +		idle-states {
> +			CPU_PWRDN: cpu-power-down {
> +				compatible = "arm,idle-state";
> +				arm,psci-suspend-param = <0x0000001>;
> +				entry-latency-us = <10>;
> +				exit-latency-us = <10>;
> +				min-residency-us = <100>;
> +			};
> +
> +			CLUSTER_RET: cluster-retention {
> +				compatible = "domain-idle-state";
> +				arm,psci-suspend-param = <0x1000010>;
> +				entry-latency-us = <500>;
> +				exit-latency-us = <500>;
> +				min-residency-us = <2000>;
> +			};
> +
> +			CLUSTER_PWRDN: cluster-power-down {
> +				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-pd0 {
> +			#power-domain-cells = <0>;
> +			domain-idle-states = <&CPU_PWRDN>;
> +			power-domains = <&CLUSTER_PD>;
> +		};
> +
> +		CPU_PD1: cpu-pd1 {
> +			#power-domain-cells = <0>;
> +			domain-idle-states =  <&CPU_PWRDN>;
> +			power-domains = <&CLUSTER_PD>;
> +		};
> +
> +		CLUSTER_PD: cluster-pd {
> +			#power-domain-cells = <0>;
> +			domain-idle-states = <&CLUSTER_RET>, <&CLUSTER_PWRDN>;
> +		};
> +	};
> +
>  [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
> -- 
> 2.17.1
>