[PATCH RFC v5 3/3] Documentation: arm: define DT idle states bindings
Lorenzo Pieralisi
lorenzo.pieralisi at arm.com
Mon Apr 7 07:36:22 PDT 2014
On Mon, Apr 07, 2014 at 01:25:17PM +0100, Vincent Guittot wrote:
> On 4 April 2014 17:56, Lorenzo Pieralisi <lorenzo.pieralisi at arm.com> wrote:
> > [replying to self, since I have a query]
> >
> > [...]
> >
> >> +===========================================
> >> +4 - Examples
> >> +===========================================
> >> +
> >> +Example 1 (ARM 64-bit, 16-cpu system):
> >> +
> >> +pd_clusters: power-domain-clusters at 80002000 {
> >> + compatible = "arm,power-controller";
> >> + reg = <0x0 0x80002000 0x0 0x1000>;
> >> + #power-domain-cells = <1>;
> >> + #address-cells = <2>;
> >> + #size-cells = <2>;
> >> +
> >> + pd_cores: power-domain-cores at 80000000 {
> >> + compatible = "arm,power-controller";
> >> + reg = <0x0 0x80000000 0x0 0x1000>;
> >> + #power-domain-cells = <1>;
> >> + };
> >> +};
> >> +
> >> +cpus {
> >> + #size-cells = <0>;
> >> + #address-cells = <2>;
> >> +
> >> + idle-states {
> >> + entry-method = "arm,psci-cpu-suspend";
> >> +
> >> + CLUSTER_RETENTION_0: cluster-retention-0 {
> >> + compatible = "arm,idle-state";
> >> + index = <2>;
> >> + logic-state-retained;
> >> + cache-state-retained;
> >> + entry-method-param = <0x1010000>;
> >> + entry-latency-us = <50>;
> >> + exit-latency-us = <100>;
> >> + min-residency-us = <250>;
> >> + power-domains = <&pd_clusters 0>;
> >> + CPU_RETENTION_0_0: cpu-retention-0 {
> >> + compatible = "arm,idle-state";
> >> + index = <0>;
> >> + cache-state-retained;
> >> + entry-method-param = <0x0010000>;
> >> + entry-latency-us = <20>;
> >> + exit-latency-us = <40>;
> >> + min-residency-us = <30>;
> >> + power-domains = <&pd_cores 0>,
> >> + <&pd_cores 1>,
> >> + <&pd_cores 2>,
> >> + <&pd_cores 3>,
> >> + <&pd_cores 4>,
> >> + <&pd_cores 5>,
> >> + <&pd_cores 6>,
> >> + <&pd_cores 7>;
> >> + };
> >> + };
> >> +
> >> + CLUSTER_SLEEP_0: cluster-sleep-0 {
> >> + compatible = "arm,idle-state";
> >> + index = <3>;
> >> + entry-method-param = <0x1010000>;
> >> + entry-latency-us = <600>;
> >> + exit-latency-us = <1100>;
> >> + min-residency-us = <2700>;
> >> + power-domains = <&pd_clusters 0>;
> >> + CPU_SLEEP_0_0: cpu-sleep-0 {
> >> + /* cpu sleep */
> >> + compatible = "arm,idle-state";
> >> + index = <1>;
> >> + entry-method-param = <0x0010000>;
> >> + entry-latency-us = <250>;
> >> + exit-latency-us = <500>;
> >> + min-residency-us = <350>;
> >> + power-domains = <&pd_cores 0>,
> >> + <&pd_cores 1>,
> >> + <&pd_cores 2>,
> >> + <&pd_cores 3>,
> >> + <&pd_cores 4>,
> >> + <&pd_cores 5>,
> >> + <&pd_cores 6>,
> >> + <&pd_cores 7>;
> >> + };
> >> + };
> >
> > I noticed while developing the CPUidle generic driver, that by using this
> > representation I might end up requiring duplicated states.
> >
> > For instance, a cluster-retention state and a cluster-sleep state might
> > want to have cpu-sleep state as substate, and this would require an
> > idle state node duplication.
> >
> > I think it is better to have a single flat (and ordered...that would
> > kill two birds with one stone) list of nodes in the idle-states node and
> > every state might have a list of phandles to subnodes (substates), something
> > like the following example.
> >
> > This simplifies parsing and I think it solves the last issue I
> > came across (the need for duplicate states - in the bindings below,
> > CPU_SLEEP_0 is a substate of both CLUSTER_RETENTION_0 and
> > CLUSTER_SLEEP_0, through phandles).
>
> Hi Lorenzo,
>
> You explanation above has triggered a question. You writes:
> CPU_SLEEP_0 is a substate of CLUSTER_RETENTION_0 but i would have say
> that both CPU_SLEEP_0 and CPU_RETENTION_0 are substates of
> CLUSTER_RETENTION_0. I mean that if cpus are either in retention mode
> OR in sleep mode, you can enter the CLUSTER_RETENTION_0 state (you
> can have some in sleep mode and other in retention of course)
> I'm wondering how this OR will be described.
We need another state (because that's what happens in HW right ?), so we
describe it (obviously having different latencies):
CLUSTER_RETENTION_1: cluster-retention-1 {
compatible = "arm,idle-state";
logic-state-retained;
cache-state-retained;
entry-method-param = <0x1010000>;
entry-latency-us = <50>;
exit-latency-us = <700>;
min-residency-us = <2000>;
power-domains = <&pd_clusters 0>;
substates = <&CPU_RETENTION_0>;
};
Using phandles all state combinations are now possible, with no state
duplication.
State above is entered when all CPUs are in retention mode and thanks
to the phandle the kernel knows what has to be done as far as each
CPU is concerned. The beauty of this approach is that for every state,
it is well defined what has to be done for the respective power domain
(eg state above, cache is retained. All caches in <&pd_clusters 0> are
retained. Then we follow the substates, and take action according to
the substate propertes and respective power domain).
Does this make sense ? I can't find fault with this semantics, but
please let me know if you do.
Thank you !!
Lorenzo
> Then, IMHO, the flat description below is clearer and remove the
> duplicated description that you mention previously
>
> Regards,
> Vincent
>
> >
> > Thoughts very appreciated, thanks.
> >
> > Lorenzo
> >
> > idle-states {
> > entry-method = "arm,psci-cpu-suspend";
> >
> > CPU_RETENTION_0: cpu-retention-0 {
> > compatible = "arm,idle-state";
> > cache-state-retained;
> > entry-method-param = <0x0010000>;
> > entry-latency-us = <20>;
> > exit-latency-us = <40>;
> > min-residency-us = <30>;
> > power-domains = <&pd_cores 0>,
> > <&pd_cores 1>,
> > <&pd_cores 2>,
> > <&pd_cores 3>,
> > };
> >
> > CPU_SLEEP_0: cpu-sleep-0 {
> > /* cpu sleep */
> > compatible = "arm,idle-state";
> > entry-method-param = <0x0010000>;
> > entry-latency-us = <250>;
> > exit-latency-us = <500>;
> > min-residency-us = <350>;
> > power-domains = <&pd_cores 0>,
> > <&pd_cores 1>,
> > <&pd_cores 2>,
> > <&pd_cores 3>,
> > };
> >
> > CPU_SLEEP_1: cpu-sleep-1 {
> > /* cpu sleep */
> > compatible = "arm,idle-state";
> > entry-method-param = <0x0010000>;
> > entry-latency-us = <250>;
> > exit-latency-us = <500>;
> > min-residency-us = <350>;
> > <&pd_cores 4>,
> > <&pd_cores 5>,
> > <&pd_cores 6>,
> > <&pd_cores 7>;
> > };
> >
> > CLUSTER_RETENTION_0: cluster-retention-0 {
> > compatible = "arm,idle-state";
> > logic-state-retained;
> > cache-state-retained;
> > entry-method-param = <0x1010000>;
> > entry-latency-us = <50>;
> > exit-latency-us = <800>;
> > min-residency-us = <2400>;
> > power-domains = <&pd_clusters 0>;
> > substates = <&CPU_SLEEP_0>;
> > };
> >
> > CLUSTER_SLEEP_0: cluster-sleep-0 {
> > compatible = "arm,idle-state";
> > entry-method-param = <0x1010000>;
> > entry-latency-us = <600>;
> > exit-latency-us = <1100>;
> > min-residency-us = <2700>;
> > power-domains = <&pd_clusters 0>;
> > substates = <&CPU_SLEEP_0>;
> > };
> >
> > CLUSTER_SLEEP_1: cluster-sleep-1 {
> > compatible = "arm,idle-state";
> > entry-method-param = <0x1010000>;
> > entry-latency-us = <600>;
> > exit-latency-us = <1100>;
> > min-residency-us = <2700>;
> > power-domains = <&pd_clusters 1>;
> > substates = <&CPU_SLEEP_1>;
> > };
> >
> > SYSTEM_SLEEP_0: system-sleep-0 {
> > compatible = "arm,idle-state";
> > entry-method-param = <0x2010000>;
> > entry-latency-us = <6000>;
> > exit-latency-us = <10000>;
> > min-residency-us = <30000>;
> > power-domains = <&pd_system 0>;
> > substates = <&CLUSTER_SLEEP_0>, <&CLUSTER_SLEEP_1>;
> > };
> > };
> >
>
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