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FAILED: patch "[PATCH] cpufreq: Make drivers using CPUFREQ_ETERNAL specify" failed to apply to 6.12-stable tree

PATCH New [email protected] 2 participants 2 messages Oct 15, 2025

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Stable branch Arm i.MX and Layerscape CPU frequency scaling framework Rust +1 more subsystems
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#0 lore raw

The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x f97aef092e199c10a3da96ae79b571edd5362faa
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025101528-barcode-doorstop-420a@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f97aef092e199c10a3da96ae79b571edd5362faa Mon Sep 17 00:00:00 2001
From: "Rafael J. Wysocki" <[email protected]>
Date: Fri, 26 Sep 2025 12:12:37 +0200
Subject: [PATCH] cpufreq: Make drivers using CPUFREQ_ETERNAL specify
transition latency

Commit a755d0e2d41b ("cpufreq: Honour transition_latency over transition_delay_us") caused platforms where cpuinfo.transition_latency is CPUFREQ_ETERNAL to get a very large transition latency whereas previously it had been capped at 10 ms (and later at 2 ms).

This led to a user-observable regression between 6.6 and 6.12 as described by Shawn:

"The dbs sampling_rate was 10000 us on 6.6 and suddently becomes
6442450 us (4294967295 / 1000 * 1.5) on 6.12 for these platforms because the default transition delay was dropped [...].

It slows down dbs governor's reacting to CPU loading change dramatically. Also, as transition_delay_us is used by schedutil governor as rate_limit_us, it shows a negative impact on device idle power consumption, because the device gets slightly less time in the lowest OPP."

Evidently, the expectation of the drivers using CPUFREQ_ETERNAL as cpuinfo.transition_latency was that it would be capped by the core, but they may as well return a default transition latency value instead of CPUFREQ_ETERNAL and the core need not do anything with it.

Accordingly, introduce CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS and make all of the drivers in question use it instead of CPUFREQ_ETERNAL. Also update the related Rust binding.

Fixes a755d0e2d41b ("cpufreq: Honour transition_latency over transition_delay_us")
Closes https://lore.kernel.org/linux-pm/[email protected]/ open here
Reported-by Shawn Guo <[email protected]>
Reviewed-by Mario Limonciello (AMD) <[email protected]>
Reviewed-by Jie Zhan <[email protected]>
Acked-by Viresh Kumar <[email protected]>
Cc 6.6+ <[email protected]> # 6.6+
Signed-off-by Rafael J. Wysocki <[email protected]>
Link https://patch.msgid.link/[email protected] open here
[ rjw: Fix typo in new symbol name, drop redundant type cast from Rust binding ]
Tested-by Shawn Guo <[email protected]> # with cpufreq-dt driver
Reviewed-by Qais Yousef <[email protected]>
Signed-off-by Rafael J. Wysocki <[email protected]>
drivers/cpufreq/cpufreq-dt.c +1 -1
index 506437489b4d..7d5079fd1688 100644
@@ -104,7 +104,7 @@ static int cpufreq_init(struct cpufreq_policy *policy)
 
 	transition_latency = dev_pm_opp_get_max_transition_latency(cpu_dev);
 	if (!transition_latency)
-		transition_latency = CPUFREQ_ETERNAL;
+		transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	cpumask_copy(policy->cpus, priv->cpus);
 	policy->driver_data = priv;
drivers/cpufreq/imx6q-cpufreq.c +1 -1
index db1c88e9d3f9..e93697d3edfd 100644
@@ -442,7 +442,7 @@ static int imx6q_cpufreq_probe(struct platform_device *pdev)
 	}
 
 	if (of_property_read_u32(np, "clock-latency", &transition_latency))
-		transition_latency = CPUFREQ_ETERNAL;
+		transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	/*
 	 * Calculate the ramp time for max voltage change in the
drivers/cpufreq/mediatek-cpufreq-hw.c +1 -1
index fce5aa5ceea0..ae4500ab4891 100644
@@ -309,7 +309,7 @@ static int mtk_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
 
 	latency = readl_relaxed(data->reg_bases[REG_FREQ_LATENCY]) * 1000;
 	if (!latency)
-		latency = CPUFREQ_ETERNAL;
+		latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	policy->cpuinfo.transition_latency = latency;
 	policy->fast_switch_possible = true;
drivers/cpufreq/rcpufreq_dt.rs +1 -1
index 7e1fbf9a091f..3909022e1c74 100644
@@ -123,7 +123,7 @@ fn init(policy: &mut cpufreq::Policy) -> Result<Self::PData> {
 
         let mut transition_latency = opp_table.max_transition_latency_ns() as u32;
         if transition_latency == 0 {
-            transition_latency = cpufreq::ETERNAL_LATENCY_NS;
+            transition_latency = cpufreq::DEFAULT_TRANSITION_LATENCY_NS;
         }
 
         policy
drivers/cpufreq/scmi-cpufreq.c +1 -1
index 38c165d526d1..d2a110079f5f 100644
@@ -294,7 +294,7 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
 
 	latency = perf_ops->transition_latency_get(ph, domain);
 	if (!latency)
-		latency = CPUFREQ_ETERNAL;
+		latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	policy->cpuinfo.transition_latency = latency;
drivers/cpufreq/scpi-cpufreq.c +1 -1
index dcbb0ae7dd47..e530345baddf 100644
@@ -157,7 +157,7 @@ static int scpi_cpufreq_init(struct cpufreq_policy *policy)
 
 	latency = scpi_ops->get_transition_latency(cpu_dev);
 	if (!latency)
-		latency = CPUFREQ_ETERNAL;
+		latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	policy->cpuinfo.transition_latency = latency;
drivers/cpufreq/spear-cpufreq.c +1 -1
index 707c71090cc3..2a1550e1aa21 100644
@@ -182,7 +182,7 @@ static int spear_cpufreq_probe(struct platform_device *pdev)
 
 	if (of_property_read_u32(np, "clock-latency",
 				&spear_cpufreq.transition_latency))
-		spear_cpufreq.transition_latency = CPUFREQ_ETERNAL;
+		spear_cpufreq.transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	cnt = of_property_count_u32_elems(np, "cpufreq_tbl");
 	if (cnt <= 0) {
include/linux/cpufreq.h +3 -0
index 40966512ea18..bc8c083bc16a 100644
@@ -32,6 +32,9 @@
  */
 
 #define CPUFREQ_ETERNAL			(-1)
+
+#define CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS	NSEC_PER_MSEC
+
 #define CPUFREQ_NAME_LEN		16
 /* Print length for names. Extra 1 space for accommodating '\n' in prints */
 #define CPUFREQ_NAME_PLEN		(CPUFREQ_NAME_LEN + 1)
rust/kernel/cpufreq.rs +4 -3
index eea57ba95f24..2ea735700ae7 100644
@@ -39,7 +39,8 @@
 const CPUFREQ_NAME_LEN: usize = bindings::CPUFREQ_NAME_LEN as usize;
 
 /// Default transition latency value in nanoseconds.
-pub const ETERNAL_LATENCY_NS: u32 = bindings::CPUFREQ_ETERNAL as u32;
+pub const DEFAULT_TRANSITION_LATENCY_NS: u32 =
+        bindings::CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 /// CPU frequency driver flags.
 pub mod flags {

@@ -400,13 +401,13 @@ pub fn to_table(mut self) -> Result<TableBox> {
 /// The following example demonstrates how to create a CPU frequency table.
 ///
 /// ```
-/// use kernel::cpufreq::{ETERNAL_LATENCY_NS, Policy};
+/// use kernel::cpufreq::{DEFAULT_TRANSITION_LATENCY_NS, Policy};
 ///
 /// fn update_policy(policy: &mut Policy) {
 ///     policy
 ///         .set_dvfs_possible_from_any_cpu(true)
 ///         .set_fast_switch_possible(true)
-///         .set_transition_latency_ns(ETERNAL_LATENCY_NS);
+///         .set_transition_latency_ns(DEFAULT_TRANSITION_LATENCY_NS);
 ///
 ///     pr_info!("The policy details are: {:?}\n", (policy.cpu(), policy.cur()));
 /// }
maintainer
#1 lore raw

PATCH 1/1 cpufreq: Make drivers using CPUFREQ_ETERNAL specify transition latency

From: "Rafael J. Wysocki" <[email protected]>

[ Upstream commit f97aef092e199c10a3da96ae79b571edd5362faa ]

Commit a755d0e2d41b ("cpufreq: Honour transition_latency over transition_delay_us") caused platforms where cpuinfo.transition_latency is CPUFREQ_ETERNAL to get a very large transition latency whereas previously it had been capped at 10 ms (and later at 2 ms).

This led to a user-observable regression between 6.6 and 6.12 as described by Shawn:

"The dbs sampling_rate was 10000 us on 6.6 and suddently becomes
6442450 us (4294967295 / 1000 * 1.5) on 6.12 for these platforms because the default transition delay was dropped [...].

It slows down dbs governor's reacting to CPU loading change dramatically. Also, as transition_delay_us is used by schedutil governor as rate_limit_us, it shows a negative impact on device idle power consumption, because the device gets slightly less time in the lowest OPP."

Evidently, the expectation of the drivers using CPUFREQ_ETERNAL as cpuinfo.transition_latency was that it would be capped by the core, but they may as well return a default transition latency value instead of CPUFREQ_ETERNAL and the core need not do anything with it.

Accordingly, introduce CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS and make all of the drivers in question use it instead of CPUFREQ_ETERNAL. Also update the related Rust binding.

Fixes a755d0e2d41b ("cpufreq: Honour transition_latency over transition_delay_us")
Closes https://lore.kernel.org/linux-pm/[email protected]/ open here
Reported-by Shawn Guo <[email protected]>
Reviewed-by Mario Limonciello (AMD) <[email protected]>
Reviewed-by Jie Zhan <[email protected]>
Acked-by Viresh Kumar <[email protected]>
Cc 6.6+ <[email protected]> # 6.6+
Signed-off-by Rafael J. Wysocki <[email protected]>
Link https://patch.msgid.link/[email protected] open here
[ rjw: Fix typo in new symbol name, drop redundant type cast from Rust binding ]
Tested-by Shawn Guo <[email protected]> # with cpufreq-dt driver
Reviewed-by Qais Yousef <[email protected]>
Signed-off-by Rafael J. Wysocki <[email protected]>
[ omitted Rust changes ]
Signed-off-by Sasha Levin <[email protected]>
---
 drivers/cpufreq/cpufreq-dt.c          | 2 +-
 drivers/cpufreq/imx6q-cpufreq.c       | 2 +-
 drivers/cpufreq/mediatek-cpufreq-hw.c | 2 +-
 drivers/cpufreq/scmi-cpufreq.c        | 2 +-
 drivers/cpufreq/scpi-cpufreq.c        | 2 +-
 drivers/cpufreq/spear-cpufreq.c       | 2 +-
 include/linux/cpufreq.h               | 3 +++
 7 files changed, 9 insertions(+), 6 deletions(-)
drivers/cpufreq/cpufreq-dt.c +1 -1
index 983443396f8f2..30e1b64d0558f 100644
@@ -110,7 +110,7 @@ static int cpufreq_init(struct cpufreq_policy *policy)
 
 	transition_latency = dev_pm_opp_get_max_transition_latency(cpu_dev);
 	if (!transition_latency)
-		transition_latency = CPUFREQ_ETERNAL;
+		transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	cpumask_copy(policy->cpus, priv->cpus);
 	policy->driver_data = priv;
drivers/cpufreq/imx6q-cpufreq.c +1 -1
index c20d3ecc5a81e..33c1df7f683e4 100644
@@ -443,7 +443,7 @@ static int imx6q_cpufreq_probe(struct platform_device *pdev)
 	}
 
 	if (of_property_read_u32(np, "clock-latency", &transition_latency))
-		transition_latency = CPUFREQ_ETERNAL;
+		transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	/*
 	 * Calculate the ramp time for max voltage change in the
drivers/cpufreq/mediatek-cpufreq-hw.c +1 -1
index aeb5e63045421..1f1ec43aad7ca 100644
@@ -238,7 +238,7 @@ static int mtk_cpufreq_hw_cpu_init(struct cpufreq_policy *policy)
 
 	latency = readl_relaxed(data->reg_bases[REG_FREQ_LATENCY]) * 1000;
 	if (!latency)
-		latency = CPUFREQ_ETERNAL;
+		latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	policy->cpuinfo.transition_latency = latency;
 	policy->fast_switch_possible = true;
drivers/cpufreq/scmi-cpufreq.c +1 -1
index a2ec1addafc93..bb265541671a5 100644
@@ -280,7 +280,7 @@ static int scmi_cpufreq_init(struct cpufreq_policy *policy)
 
 	latency = perf_ops->transition_latency_get(ph, domain);
 	if (!latency)
-		latency = CPUFREQ_ETERNAL;
+		latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	policy->cpuinfo.transition_latency = latency;
drivers/cpufreq/scpi-cpufreq.c +1 -1
index a191d9bdf667a..bdbc3923629e7 100644
@@ -157,7 +157,7 @@ static int scpi_cpufreq_init(struct cpufreq_policy *policy)
 
 	latency = scpi_ops->get_transition_latency(cpu_dev);
 	if (!latency)
-		latency = CPUFREQ_ETERNAL;
+		latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	policy->cpuinfo.transition_latency = latency;
drivers/cpufreq/spear-cpufreq.c +1 -1
index d8ab5b01d46d0..c032dd5d12d3c 100644
@@ -183,7 +183,7 @@ static int spear_cpufreq_probe(struct platform_device *pdev)
 
 	if (of_property_read_u32(np, "clock-latency",
 				&spear_cpufreq.transition_latency))
-		spear_cpufreq.transition_latency = CPUFREQ_ETERNAL;
+		spear_cpufreq.transition_latency = CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS;
 
 	cnt = of_property_count_u32_elems(np, "cpufreq_tbl");
 	if (cnt <= 0) {
include/linux/cpufreq.h +3 -0
index a604c54ae44da..794e38320f568 100644
@@ -32,6 +32,9 @@
  */
 
 #define CPUFREQ_ETERNAL			(-1)
+
+#define CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS	NSEC_PER_MSEC
+
 #define CPUFREQ_NAME_LEN		16
 /* Print length for names. Extra 1 space for accommodating '\n' in prints */
 #define CPUFREQ_NAME_PLEN		(CPUFREQ_NAME_LEN + 1)
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