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Subject[RFC 0/7] Managing cluser-level c-states with generic power domains


3) URL


This patch set's underlying idea is that cluster-level c-states can be managed
by the power domain, building upon Lina Iyers recent work on CPU-domain, and Axel Haslam's
genpd multiple states. The power domain may contain CPU devices and non-CPU devices.

Non-CPU Devices may expose latency constraints by registering intermediate power-states upon
probing, for instance shallower states than the deepest cluster-off state. The generic
power domain governor may chose a device retention state in place of the cluster-sleep
state demanded by the menu governor, and call the platform specific handling to enter/leave
that retention state.


The proposed way how cluster-level c-states are declared as manageable by the
power domain, rather than through the cpuidle-ops, relies on the introduction of
"power-states", consistent with c-states. Here is an example of the DT bindings,
the c-state CLUSTER_SLEEP_0 is exposed as a power-state in the compatible property:

juno.dts: idle-states {
entry-method = "arm,psci";

CPU_SLEEP_0: cpu-sleep-0 {
compatible = "arm,idle-state";
arm,psci-suspend-param = <0x0010000>;
entry-latency-us = <100>;
exit-latency-us = <250>;
min-residency-us = <2000>;

CLUSTER_SLEEP_0: cluster-sleep-0 {
compatible = "arm,power-state";
arm,psci-suspend-param = <0x1010000>;
entry-latency-us = <800>;
exit-latency-us = <700>;
min-residency-us = <2500>;

This will tell cpuidle runtime_put/get the CPU devices for this c-state. Eventually, the
actual platform handlers may be called from the genpd platform ops (in place of cpuidle_ops).


static const struct of_device_id arm_idle_state_match[] __initconst = {
{.compatible = "arm,idle-state",
.data = arm_enter_idle_state},
{.compatible = "arm,power-state",
.data = arm_enter_power_state},

In case of a power-state, arm_enter_power_state will only call pm_runtime_put/get_sync
The power doamin will handle the power off, currently this patch set lacks the final
call to the psci interface to have a fully fonctionnal setup
(and there are some genpd_lock'ing issues if put/get actually suspend the CPU device.)

Ultimately, we would like the Power Domain's simple governor to being able to chose
the cluster power-state based on the c-states defered to it (power-states) and constraints
added by the devices. Consequently, we need to "soak" those power-states into the
power-domain intermediate states from Axel. Since power-states are declared and handled
the same manner than c-states (idle-states in DT), these patches add a soaking used when
attaching to a genpd, where power-states are parsed from the DT into the genpd states:


static const struct of_device_id power_state_match[] = {
{.compatible = "arm,power-state",

int of_genpd_device_parse_states(struct device_node *np,
struct generic_pm_domain *genpd)

debugfs addition

To easy debug, this patch set adds a seq-file names "states" to the pm_genpd debugfs:

cat /sys/kernel/debug/pm_genpd/*

Domain State name Enter (ns) / Exit (ns)
a53_pd cluster-sleep-0 1500000 / 800000
a57_pd cluster-sleep-0 1500000 / 800000

And also a seq-file "timings", to help visualize the constrains of the non-CPU
devices in a cluster PD.

Domain Devices, Timings in ns
Stop/Start Save/Restore, Effective
---------------------------------------------------- ---
/cpus/cpu@0 800 /740 1320 /1720 ,0 (cached stop)
/cpus/cpu@1 800 /740 1420 /1780 ,0 (cached stop)
/D1 660 /580 16560 /6080 ,2199420 (cached stop)

Device power-states

some devices, like L2 caches, may feature a shallower retention mode, between CPU_SLEEP_0
and CLUSTER_SLEEP_0, in which mode the L2 memory is not powered off, leading to faster
resume than CLUSTER_SLEEP_0.

One way to handle device constrains and retention features in the power-domain, is to
allow devices to register a new power-state (consistent with a c-state).


D1_RETENTION: d1-retention {
compatible = "arm,power-state";
/*leave the psci param, for demo/testing:
* the psci cpuidle driver will not currently
* understand that a c-state shall not have it's
* table entry with a firmware command.
* the actual .power_on/off would be registered
* by the DECLARE macro for a given domain*/
arm,psci-suspend-param = <0x1010000>;
entry-latency-us = <800>;
exit-latency-us = <200>;
min-residency-us = <2500>;

D1 {
compatible = "fake,fake-driver";
name = "D1";
constraint = <30000>;
power-domains = <&a53_pd>;
power-states =<&D1_RETENTION>;

The genpd simple governor can now upon suspend of the last-man CPU chose a shallower
retention state than CLUSTER_SLEEP_0.

In order to achieve this, this patch set added the power-state parsing during the
genpd_dev_pm_attach call. Multiple genpd states are now inserted in a sorted manner
according to their depth: see pm_genpd_insert_state in "drivers/base/power/domain.c".


This patch set applies over linux-4.2rc5 plus the following ordered dependencies:

* Ulf Hansson:

6637131 New [V4] PM / Domains: Remove intermediate states from the power off sequence

* Lina Iyer's patch series:

6945201 New [1/9] PM / Domains: Allocate memory outside domain locks
6945221 New [2/9] PM / Domains: Remove dev->driver check for runtime PM
6945231 New [3/9] PM / Domains: Support IRQ safe PM domains
6945211 New [4/9] kernel/cpu_pm: fix cpu_cluster_pm_exit comment
6945251 New [5/9] ARM: common: Introduce PM domains for CPUs/clusters
6945281 New [6/9] ARM: domain: Add platform handlers for CPU PM domains
6945261 New [7/9] ARM: cpuidle: Add runtime PM support for CPU idle
6945241 New [8/9] ARM64: smp: Add runtime PM support for CPU hotplug
6945271 New [9/9] ARM: smp: Add runtime PM support for CPU hotplug

* John Medhurst:

6303671 New arm64: dts: Add idle-states for Juno

* Axel Haslam:

7b4eda6 ARM: imx6: pm: declare pm domain latency on power_state struct.
e65789a PM / Domains: make governor select deepest state
8b22b90 PM / Domains: core changes for multiple states
84af098 PM / Domains: prepare for multiple states

2) URL

playable from

by adding the "fake driver D1" and launching the script.
this will show the power domain suspending to an intermediate state, based on the
device constraints.

domain status pstate slaves
/device runtime status
a53_pd on
/devices/system/cpu/cpu0 active
/devices/system/cpu/cpu3 suspended
/devices/system/cpu/cpu4 suspended
/devices/system/cpu/cpu5 suspended
a57_pd d1-retention
/devices/system/cpu/cpu1 suspended
/devices/system/cpu/cpu2 suspended


Marc Titinger (7):
arm64: pm/domains: try mutualize CPU domains init between arm/arm64
arm64: Juno: declare generic power domains for both clusters.
PM / Domains: prepare for devices that might register a power state
PM / Domains: introduce power-states consistent with c-states.
PM / Domains: succeed & warn when attaching non-irqsafe devices to an
irq-safe domain.
arm: cpuidle: let genpd handle the cluster power transition with
PM / Domains: add debugfs 'states' and 'timings' seq files

.../devicetree/bindings/arm/idle-states.txt | 21 +-
.../devicetree/bindings/power/power_domain.txt | 29 ++
arch/arm/common/domains.c | 9 +-
arch/arm64/Kconfig | 1 +
arch/arm64/boot/dts/arm/juno.dts | 25 +-
arch/arm64/include/asm/arm-pd.h | 1 +
arch/arm64/kernel/Makefile | 6 +
arch/arm64/kernel/domains.c | 1 +
drivers/base/power/domain.c | 418 +++++++++++++++------
drivers/cpuidle/cpuidle-arm.c | 50 ++-
include/linux/pm_domain.h | 21 +-
11 files changed, 452 insertions(+), 130 deletions(-)
create mode 120000 arch/arm64/include/asm/arm-pd.h
create mode 120000 arch/arm64/kernel/domains.c


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