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 stable@vger.kernel.org.

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 'stable@vger.kernel.org' --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" rafael.j.wysocki@intel.com 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/20250922125929.453444-1-shawnguo2@yeah.net/ Reported-by: Shawn Guo shawnguo@kernel.org Reviewed-by: Mario Limonciello (AMD) superm1@kernel.org Reviewed-by: Jie Zhan zhanjie9@hisilicon.com Acked-by: Viresh Kumar viresh.kumar@linaro.org Cc: 6.6+ stable@vger.kernel.org # 6.6+ Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com Link: https://patch.msgid.link/2264949.irdbgypaU6@rafael.j.wysocki [ rjw: Fix typo in new symbol name, drop redundant type cast from Rust binding ] Tested-by: Shawn Guo shawnguo@kernel.org # with cpufreq-dt driver Reviewed-by: Qais Yousef qyousef@layalina.io Signed-off-by: Rafael J. Wysocki rafael.j.wysocki@intel.com

diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c index 506437489b4d..7d5079fd1688 100644 --- a/drivers/cpufreq/cpufreq-dt.c +++ b/drivers/cpufreq/cpufreq-dt.c @@ -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; diff --git a/drivers/cpufreq/imx6q-cpufreq.c b/drivers/cpufreq/imx6q-cpufreq.c index db1c88e9d3f9..e93697d3edfd 100644 --- a/drivers/cpufreq/imx6q-cpufreq.c +++ b/drivers/cpufreq/imx6q-cpufreq.c @@ -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 diff --git a/drivers/cpufreq/mediatek-cpufreq-hw.c b/drivers/cpufreq/mediatek-cpufreq-hw.c index fce5aa5ceea0..ae4500ab4891 100644 --- a/drivers/cpufreq/mediatek-cpufreq-hw.c +++ b/drivers/cpufreq/mediatek-cpufreq-hw.c @@ -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; diff --git a/drivers/cpufreq/rcpufreq_dt.rs b/drivers/cpufreq/rcpufreq_dt.rs index 7e1fbf9a091f..3909022e1c74 100644 --- a/drivers/cpufreq/rcpufreq_dt.rs +++ b/drivers/cpufreq/rcpufreq_dt.rs @@ -123,7 +123,7 @@ fn init(policy: &mut cpufreq::Policy) -> ResultSelf::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 diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c index 38c165d526d1..d2a110079f5f 100644 --- a/drivers/cpufreq/scmi-cpufreq.c +++ b/drivers/cpufreq/scmi-cpufreq.c @@ -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;

diff --git a/drivers/cpufreq/scpi-cpufreq.c b/drivers/cpufreq/scpi-cpufreq.c index dcbb0ae7dd47..e530345baddf 100644 --- a/drivers/cpufreq/scpi-cpufreq.c +++ b/drivers/cpufreq/scpi-cpufreq.c @@ -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;

diff --git a/drivers/cpufreq/spear-cpufreq.c b/drivers/cpufreq/spear-cpufreq.c index 707c71090cc3..2a1550e1aa21 100644 --- a/drivers/cpufreq/spear-cpufreq.c +++ b/drivers/cpufreq/spear-cpufreq.c @@ -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) { diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h index 40966512ea18..bc8c083bc16a 100644 --- a/include/linux/cpufreq.h +++ b/include/linux/cpufreq.h @@ -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) diff --git a/rust/kernel/cpufreq.rs b/rust/kernel/cpufreq.rs index eea57ba95f24..2ea735700ae7 100644 --- a/rust/kernel/cpufreq.rs +++ b/rust/kernel/cpufreq.rs @@ -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())); /// }