[PATCH v2 0/3] PM: QoS/pmdomains: support resume latencies for system-wide PM

[PATCH v2 0/3] PM: QoS/pmdomains: support resume latencies for system-wide PM

[Kevin Hilman (TI)]

Currently QoS resume latencies are only considered for runtime PM
transitions of pmdomains, which remains the default.

In order to also support QoS resume latencies during system-wide PM,
add a new flag to indicate a resume latency should be used for
system-wide PM *in addition to* runtime PM.

If a user requires a different latency value for system-wide PM
compared to runtime PM, then the runtime PM value can be set for
normal operations, and the system-wide value (and flag) can be set by
during suspend (for example in a drivers ->prepare() hook) and the
runtime PM value can be restored after resume (for example, in a
driver's ->complete() hook.)

To: Rafael J. Wysocki <rafael@kernel.org>
To: Ulf Hansson <ulf.hansson@linaro.org>
To: linux-pm@vger.kernel.org

Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
---
Changes in v2:
- drop the userspace interface
- add genpd helper to iterate over all devices in domain and child domains
- new flag means latency applies to runtime PM *and* system-wide PM
- Link to v1: https://patch.msgid.link/20260120-topic-lpm-pmdomain-device-constraints-v1-0-108fc4cfafce@baylibre.com

---
Kevin Hilman (TI) (3):
      PM / QoS: add flag to indicate latency applies system-wide
      pmdomain: core: add genpd_for_each_child() helper
      pmdommain: add support system-wide resume latency constraints

 drivers/pmdomain/core.c     | 42 ++++++++++++++++++++++++++++++++++++++++++
 drivers/pmdomain/core.h     | 17 +++++++++++++++++
 drivers/pmdomain/governor.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/pm_qos.h      |  2 ++
 4 files changed, 106 insertions(+)
---
base-commit: 3e7f562e20ee87a25e104ef4fce557d39d62fa85
change-id: 20260120-topic-lpm-pmdomain-device-constraints-e5e78ce48502

Best regards,
--  
Kevin Hilman (TI) <khilman@baylibre.com>

[PATCH v2 1/3] PM / QoS: add flag to indicate latency applies system-wide

[Kevin Hilman (TI)]

By default, the QoS resume latency currenly only applied to runtime PM
decisions.

Add new PM_QOS_FLAG_LATENCY_SYS flag to indicate that the
resume latency QoS constraint should be applied to system-wide
PM *in addition to* runtime PM.

Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
---
 include/linux/pm_qos.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
index 6cea4455f867..aededda52b6b 100644
--- a/include/linux/pm_qos.h
+++ b/include/linux/pm_qos.h
@@ -37,6 +37,8 @@ enum pm_qos_flags_status {
 #define PM_QOS_LATENCY_TOLERANCE_NO_CONSTRAINT	(-1)
 
 #define PM_QOS_FLAG_NO_POWER_OFF	(1 << 0)
+/* latency value applies to system-wide suspend/s2idle */
+#define PM_QOS_FLAG_LATENCY_SYS		(2 << 0)
 
 enum pm_qos_type {
 	PM_QOS_UNITIALIZED,

-- 
2.51.0

[PATCH v2 2/3] pmdomain: core: add genpd_for_each_child() helper

[Kevin Hilman (TI)]

Add a new internal helper function genpd_for_each_child() that recursively
iterates over all devices in a PM domain and its child domains (subdomains).
This helper is useful for governors and other core PM domain code that needs
to examine or apply operations to all devices within a domain hierarchy.

The function takes a callback that is invoked for each device, and supports
early termination if the callback returns a non-zero value.

The helper is defined in a new internal header drivers/pmdomain/core.h and
implemented in drivers/pmdomain/core.c, making it available to other PM
domain subsystem components.

The first user of this helper is the cpu_system_power_down_ok() governor
function, which uses it to check device QoS latency constraints across the
entire domain hierarchy.

Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
---
 drivers/pmdomain/core.c | 42 ++++++++++++++++++++++++++++++++++++++++++
 drivers/pmdomain/core.h | 17 +++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
index bf82775f6a67..41c987fc5c5a 100644
--- a/drivers/pmdomain/core.c
+++ b/drivers/pmdomain/core.c
@@ -24,6 +24,8 @@
 #include <linux/cpu.h>
 #include <linux/debugfs.h>
 
+#include "core.h"
+
 /* Provides a unique ID for each genpd device */
 static DEFINE_IDA(genpd_ida);
 
@@ -281,6 +283,46 @@ static void genpd_sd_counter_inc(struct generic_pm_domain *genpd)
 	smp_mb__after_atomic();
 }
 
+/**
+ * genpd_for_each_child - Recursively iterate over all devices
+ *                        in a PM domain and its subdomains.
+ * @genpd: PM domain to iterate over.
+ * @fn: Callback function to invoke for each device.
+ * @data: Data to pass to the callback function.
+ *
+ * This function recursively walks through all devices in the given PM domain
+ * and all devices in its child PM domains (subdomains). For each device found,
+ * the callback function @fn is invoked with the device and @data as arguments.
+ *
+ * Returns: 0 on success, or the first non-zero value returned by @fn.
+ */
+int genpd_for_each_child(struct generic_pm_domain *genpd,
+			 int (*fn)(struct device *dev, void *data),
+			 void *data)
+{
+	struct pm_domain_data *pdd;
+	struct gpd_link *link;
+	int ret;
+
+	/* First, iterate over all devices in this domain */
+	list_for_each_entry(pdd, &genpd->dev_list, list_node) {
+		ret = fn(pdd->dev, data);
+		if (ret)
+			return ret;
+	}
+
+	/* Then, recursively iterate over all child domains (subdomains) */
+	list_for_each_entry(link, &genpd->parent_links, parent_node) {
+		struct generic_pm_domain *child_pd = link->child;
+
+		ret = genpd_for_each_child(child_pd, fn, data);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
 #ifdef CONFIG_DEBUG_FS
 static struct dentry *genpd_debugfs_dir;
 
diff --git a/drivers/pmdomain/core.h b/drivers/pmdomain/core.h
new file mode 100644
index 000000000000..7061891d31fb
--- /dev/null
+++ b/drivers/pmdomain/core.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Internal header for PM domain core
+ *
+ * Copyright (C) 2011 Rafael J. Wysocki <rjw@sisk.pl>, Renesas Electronics Corp.
+ */
+
+#ifndef __PM_DOMAIN_CORE_H__
+#define __PM_DOMAIN_CORE_H__
+
+#include <linux/pm_domain.h>
+
+int genpd_for_each_child(struct generic_pm_domain *genpd,
+			 int (*fn)(struct device *dev, void *data),
+			 void *data);
+
+#endif /* __PM_DOMAIN_CORE_H__ */

-- 
2.51.0

[PATCH v2 3/3] pmdommain: add support system-wide resume latency constraints

[Kevin Hilman (TI)]

In addition to checking for CPU latency constraints when checking if
OK to power down a domain, also check for QoS latency constraints in
all devices of a domain and use that in determining the final latency
constraint to use for the domain.

Since cpu_system_power_down_ok() is used for system-wide suspend, the
per-device constratints are only relevant if the LATENCY_SYS QoS flag
is set.

Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
---
 drivers/pmdomain/governor.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/pmdomain/governor.c b/drivers/pmdomain/governor.c
index 96737abbb496..bbf59b93c8b6 100644
--- a/drivers/pmdomain/governor.c
+++ b/drivers/pmdomain/governor.c
@@ -13,6 +13,8 @@
 #include <linux/cpumask.h>
 #include <linux/ktime.h>
 
+#include "core.h"
+
 static int dev_update_qos_constraint(struct device *dev, void *data)
 {
 	s64 *constraint_ns_p = data;
@@ -425,17 +427,60 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
 	return true;
 }
 
+/**
+ * check_device_qos_latency - Callback to check device QoS latency constraints
+ * @dev: Device to check
+ * @data: Pointer to s32 variable holding minimum latency found so far
+ *
+ * This callback checks if the device has a system-wide resume latency QoS
+ * constraint and updates the minimum latency if this device has a stricter
+ * constraint.
+ *
+ * Returns: 0 to continue iteration.
+ */
+static int check_device_qos_latency(struct device *dev, void *data)
+{
+	s32 *min_dev_latency = data;
+	enum pm_qos_flags_status flag_status;
+	s32 dev_latency;
+
+	dev_latency = dev_pm_qos_read_value(dev, DEV_PM_QOS_RESUME_LATENCY);
+	flag_status = dev_pm_qos_flags(dev, PM_QOS_FLAG_LATENCY_SYS);
+	if ((dev_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) &&
+	    (flag_status == PM_QOS_FLAGS_ALL)) {
+		dev_dbg(dev,
+			"has QoS system-wide resume latency=%d\n",
+			dev_latency);
+		if (dev_latency < *min_dev_latency)
+			*min_dev_latency = dev_latency;
+	}
+
+	return 0;
+}
+
 static bool cpu_system_power_down_ok(struct dev_pm_domain *pd)
 {
 	s64 constraint_ns = cpu_wakeup_latency_qos_limit() * NSEC_PER_USEC;
 	struct generic_pm_domain *genpd = pd_to_genpd(pd);
 	int state_idx = genpd->state_count - 1;
+	s32 min_dev_latency = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
+	s64 min_dev_latency_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
 
 	if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN)) {
 		genpd->state_idx = state_idx;
 		return true;
 	}
 
+	genpd_for_each_child(genpd, check_device_qos_latency,
+			     &min_dev_latency);
+
+	/* If device latency < CPU wakeup latency, use it instead */
+	if (min_dev_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) {
+		min_dev_latency_ns = min_dev_latency * NSEC_PER_USEC;
+		if (min_dev_latency_ns < constraint_ns)
+			constraint_ns = min_dev_latency_ns;
+	}
+
 	/* Find the deepest state for the latency constraint. */
 	while (state_idx >= 0) {
 		s64 latency_ns = genpd->states[state_idx].power_off_latency_ns +

-- 
2.51.0

Re: [PATCH v2 1/3] PM / QoS: add flag to indicate latency applies system-wide

[Rafael J. Wysocki]

On Fri, Feb 6, 2026 at 1:30 AM Kevin Hilman (TI) <khilman@baylibre.com> wrote:
>
> By default, the QoS resume latency currenly only applied to runtime PM
> decisions.
>
> Add new PM_QOS_FLAG_LATENCY_SYS flag to indicate that the
> resume latency QoS constraint should be applied to system-wide
> PM *in addition to* runtime PM.
>
> Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>

Acked-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>

> ---
>  include/linux/pm_qos.h | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/include/linux/pm_qos.h b/include/linux/pm_qos.h
> index 6cea4455f867..aededda52b6b 100644
> --- a/include/linux/pm_qos.h
> +++ b/include/linux/pm_qos.h
> @@ -37,6 +37,8 @@ enum pm_qos_flags_status {
>  #define PM_QOS_LATENCY_TOLERANCE_NO_CONSTRAINT (-1)
>
>  #define PM_QOS_FLAG_NO_POWER_OFF       (1 << 0)
> +/* latency value applies to system-wide suspend/s2idle */
> +#define PM_QOS_FLAG_LATENCY_SYS                (2 << 0)
>
>  enum pm_qos_type {
>         PM_QOS_UNITIALIZED,
>
> --
> 2.51.0
>
>

Re: [PATCH v2 3/3] pmdommain: add support system-wide resume latency constraints

[Kendall Willis]

Hi Kevin,
On 2/5/26 18:29, Kevin Hilman (TI) wrote:
> In addition to checking for CPU latency constraints when checking if
> OK to power down a domain, also check for QoS latency constraints in
> all devices of a domain and use that in determining the final latency
> constraint to use for the domain.
> 
> Since cpu_system_power_down_ok() is used for system-wide suspend, the
> per-device constratints are only relevant if the LATENCY_SYS QoS flag
> is set.
> 
> Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
> ---

Were you planning to also check the CPU devices QoS latency constraints 
in the cpu_system_power_down_ok function? At present, this patch does 
not add that functionality so if the PM_QOS_FLAG_LATENCY_SYS is present 
for a CPU device, the QoS latency is not taken into account.

Best,
Kendall Willis <k-willis@ti.com>

Re: [PATCH v2 3/3] pmdommain: add support system-wide resume latency constraints

[Kevin Hilman]

Kendall Willis <k-willis@ti.com> writes:

> Hi Kevin,
> On 2/5/26 18:29, Kevin Hilman (TI) wrote:
>> In addition to checking for CPU latency constraints when checking if
>> OK to power down a domain, also check for QoS latency constraints in
>> all devices of a domain and use that in determining the final latency
>> constraint to use for the domain.
>> 
>> Since cpu_system_power_down_ok() is used for system-wide suspend, the
>> per-device constratints are only relevant if the LATENCY_SYS QoS flag
>> is set.
>> 
>> Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
>> ---
>
> Were you planning to also check the CPU devices QoS latency constraints 
> in the cpu_system_power_down_ok function? At present, this patch does 
> not add that functionality so if the PM_QOS_FLAG_LATENCY_SYS is present 
> for a CPU device, the QoS latency is not taken into account.

I did not add that functionality because the CPUs are managed by the new
system-wide /dev/cpu_wakeup_latency, which is already checked.

Kevin

Re: [PATCH v2 2/3] pmdomain: core: add genpd_for_each_child() helper

[Ulf Hansson]

On Fri, 6 Feb 2026 at 01:30, Kevin Hilman (TI) <khilman@baylibre.com> wrote:
>
> Add a new internal helper function genpd_for_each_child() that recursively
> iterates over all devices in a PM domain and its child domains (subdomains).
> This helper is useful for governors and other core PM domain code that needs
> to examine or apply operations to all devices within a domain hierarchy.
>
> The function takes a callback that is invoked for each device, and supports
> early termination if the callback returns a non-zero value.
>
> The helper is defined in a new internal header drivers/pmdomain/core.h and
> implemented in drivers/pmdomain/core.c, making it available to other PM
> domain subsystem components.

I think it's important to state that this isn't for pmdomain providers
to use, but only for the core and the governor. Perhaps add a comment
about that too in the function description.

That said, if there is only one user, perhaps adding a helper isn't
worth it after all?

>
> The first user of this helper is the cpu_system_power_down_ok() governor
> function, which uses it to check device QoS latency constraints across the
> entire domain hierarchy.
>
> Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
> ---
>  drivers/pmdomain/core.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  drivers/pmdomain/core.h | 17 +++++++++++++++++
>  2 files changed, 59 insertions(+)
>
> diff --git a/drivers/pmdomain/core.c b/drivers/pmdomain/core.c
> index bf82775f6a67..41c987fc5c5a 100644
> --- a/drivers/pmdomain/core.c
> +++ b/drivers/pmdomain/core.c
> @@ -24,6 +24,8 @@
>  #include <linux/cpu.h>
>  #include <linux/debugfs.h>
>
> +#include "core.h"
> +
>  /* Provides a unique ID for each genpd device */
>  static DEFINE_IDA(genpd_ida);
>
> @@ -281,6 +283,46 @@ static void genpd_sd_counter_inc(struct generic_pm_domain *genpd)
>         smp_mb__after_atomic();
>  }
>
> +/**
> + * genpd_for_each_child - Recursively iterate over all devices
> + *                        in a PM domain and its subdomains.
> + * @genpd: PM domain to iterate over.
> + * @fn: Callback function to invoke for each device.
> + * @data: Data to pass to the callback function.
> + *
> + * This function recursively walks through all devices in the given PM domain
> + * and all devices in its child PM domains (subdomains). For each device found,
> + * the callback function @fn is invoked with the device and @data as arguments.
> + *
> + * Returns: 0 on success, or the first non-zero value returned by @fn.
> + */
> +int genpd_for_each_child(struct generic_pm_domain *genpd,
> +                        int (*fn)(struct device *dev, void *data),
> +                        void *data)
> +{
> +       struct pm_domain_data *pdd;
> +       struct gpd_link *link;
> +       int ret;
> +
> +       /* First, iterate over all devices in this domain */
> +       list_for_each_entry(pdd, &genpd->dev_list, list_node) {
> +               ret = fn(pdd->dev, data);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       /* Then, recursively iterate over all child domains (subdomains) */
> +       list_for_each_entry(link, &genpd->parent_links, parent_node) {
> +               struct generic_pm_domain *child_pd = link->child;
> +
> +               ret = genpd_for_each_child(child_pd, fn, data);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       return 0;
> +}
> +
>  #ifdef CONFIG_DEBUG_FS
>  static struct dentry *genpd_debugfs_dir;
>
> diff --git a/drivers/pmdomain/core.h b/drivers/pmdomain/core.h
> new file mode 100644
> index 000000000000..7061891d31fb
> --- /dev/null
> +++ b/drivers/pmdomain/core.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Internal header for PM domain core
> + *
> + * Copyright (C) 2011 Rafael J. Wysocki <rjw@sisk.pl>, Renesas Electronics Corp.
> + */
> +
> +#ifndef __PM_DOMAIN_CORE_H__
> +#define __PM_DOMAIN_CORE_H__
> +
> +#include <linux/pm_domain.h>
> +
> +int genpd_for_each_child(struct generic_pm_domain *genpd,
> +                        int (*fn)(struct device *dev, void *data),
> +                        void *data);
> +
> +#endif /* __PM_DOMAIN_CORE_H__ */
>
> --
> 2.51.0
>

Kind regards
Uffe

Re: [PATCH v2 3/3] pmdommain: add support system-wide resume latency constraints

[Ulf Hansson]

On Fri, 6 Feb 2026 at 01:30, Kevin Hilman (TI) <khilman@baylibre.com> wrote:
>
> In addition to checking for CPU latency constraints when checking if
> OK to power down a domain, also check for QoS latency constraints in
> all devices of a domain and use that in determining the final latency
> constraint to use for the domain.
>
> Since cpu_system_power_down_ok() is used for system-wide suspend, the
> per-device constratints are only relevant if the LATENCY_SYS QoS flag
> is set.
>
> Signed-off-by: Kevin Hilman (TI) <khilman@baylibre.com>
> ---
>  drivers/pmdomain/governor.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
>
> diff --git a/drivers/pmdomain/governor.c b/drivers/pmdomain/governor.c
> index 96737abbb496..bbf59b93c8b6 100644
> --- a/drivers/pmdomain/governor.c
> +++ b/drivers/pmdomain/governor.c
> @@ -13,6 +13,8 @@
>  #include <linux/cpumask.h>
>  #include <linux/ktime.h>
>
> +#include "core.h"
> +
>  static int dev_update_qos_constraint(struct device *dev, void *data)
>  {
>         s64 *constraint_ns_p = data;
> @@ -425,17 +427,60 @@ static bool cpu_power_down_ok(struct dev_pm_domain *pd)
>         return true;
>  }
>
> +/**
> + * check_device_qos_latency - Callback to check device QoS latency constraints
> + * @dev: Device to check
> + * @data: Pointer to s32 variable holding minimum latency found so far
> + *
> + * This callback checks if the device has a system-wide resume latency QoS
> + * constraint and updates the minimum latency if this device has a stricter
> + * constraint.
> + *
> + * Returns: 0 to continue iteration.
> + */
> +static int check_device_qos_latency(struct device *dev, void *data)
> +{
> +       s32 *min_dev_latency = data;
> +       enum pm_qos_flags_status flag_status;
> +       s32 dev_latency;
> +
> +       dev_latency = dev_pm_qos_read_value(dev, DEV_PM_QOS_RESUME_LATENCY);

->cpu_system_power_down_ok() executes in atomic context on a
PREEMPT_RT configured system.

dev_pm_qos_read_value() uses spinlocks, which sleep in that configuration.

I don't know the best approach to fix this. Perhaps add a specific
dev_pm_qos interface that can be used here? Or re-work the code so it
only applies for !PREEMPT_RT?

> +       flag_status = dev_pm_qos_flags(dev, PM_QOS_FLAG_LATENCY_SYS);
> +       if ((dev_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) &&
> +           (flag_status == PM_QOS_FLAGS_ALL)) {
> +               dev_dbg(dev,
> +                       "has QoS system-wide resume latency=%d\n",
> +                       dev_latency);
> +               if (dev_latency < *min_dev_latency)
> +                       *min_dev_latency = dev_latency;
> +       }
> +
> +       return 0;
> +}
> +
>  static bool cpu_system_power_down_ok(struct dev_pm_domain *pd)
>  {
>         s64 constraint_ns = cpu_wakeup_latency_qos_limit() * NSEC_PER_USEC;
>         struct generic_pm_domain *genpd = pd_to_genpd(pd);
>         int state_idx = genpd->state_count - 1;
> +       s32 min_dev_latency = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT;
> +       s64 min_dev_latency_ns = PM_QOS_RESUME_LATENCY_NO_CONSTRAINT_NS;
>
>         if (!(genpd->flags & GENPD_FLAG_CPU_DOMAIN)) {
>                 genpd->state_idx = state_idx;
>                 return true;
>         }
>
> +       genpd_for_each_child(genpd, check_device_qos_latency,
> +                            &min_dev_latency);
> +
> +       /* If device latency < CPU wakeup latency, use it instead */
> +       if (min_dev_latency != PM_QOS_RESUME_LATENCY_NO_CONSTRAINT) {
> +               min_dev_latency_ns = min_dev_latency * NSEC_PER_USEC;
> +               if (min_dev_latency_ns < constraint_ns)
> +                       constraint_ns = min_dev_latency_ns;
> +       }
> +
>         /* Find the deepest state for the latency constraint. */
>         while (state_idx >= 0) {
>                 s64 latency_ns = genpd->states[state_idx].power_off_latency_ns +
>
> --
> 2.51.0
>

Kind regards
Uffe