cpufreq: Make drivers using CPUFREQ_ETERNAL specify transition latency

[ 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/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>
[ omitted Rust changes ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/cpufreq/cpufreq-dt.c b/drivers/cpufreq/cpufreq-dt.c
index 983443396f8f22cd8e3d48840ae4894d459a8bbe..30e1b64d0558f2ddd0edd5e1b36150904de1f739 100644 (file)
--- a/drivers/cpufreq/cpufreq-dt.c
+++ b/drivers/cpufreq/cpufreq-dt.c
@@ -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;

diff --git a/drivers/cpufreq/imx6q-cpufreq.c b/drivers/cpufreq/imx6q-cpufreq.c
index c20d3ecc5a81ea058766e4e533457fcc8a90283f..33c1df7f683e40e617216aa421837f1b7323214b 100644 (file)
--- a/drivers/cpufreq/imx6q-cpufreq.c
+++ b/drivers/cpufreq/imx6q-cpufreq.c
@@ -443,7 +443,7 @@ soc_opp_out:
        }
 
        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 aeb5e63045421b59d49bf6aa7178c6e4510c2171..1f1ec43aad7ca3e2ddac47b07f86c736ae5bd1cd 100644 (file)
--- a/drivers/cpufreq/mediatek-cpufreq-hw.c
+++ b/drivers/cpufreq/mediatek-cpufreq-hw.c
@@ -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;

diff --git a/drivers/cpufreq/scmi-cpufreq.c b/drivers/cpufreq/scmi-cpufreq.c
index a2ec1addafc931a16f6c6bd55f3d165e756f0f0c..bb265541671a58d3d20cff57cafb6eac0e40d5bf 100644 (file)
--- a/drivers/cpufreq/scmi-cpufreq.c
+++ b/drivers/cpufreq/scmi-cpufreq.c
@@ -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;
 

diff --git a/drivers/cpufreq/scpi-cpufreq.c b/drivers/cpufreq/scpi-cpufreq.c
index a191d9bdf667adcfbf4c3c32e59f3dccc83b2074..bdbc3923629e7b953668bfb82e8bfd9e39124860 100644 (file)
--- 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 d8ab5b01d46d0482900ea33d12474a857cb47481..c032dd5d12d3cc840d1aaa5f12e82cba71e6d343 100644 (file)
--- a/drivers/cpufreq/spear-cpufreq.c
+++ b/drivers/cpufreq/spear-cpufreq.c
@@ -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) {

diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h
index a604c54ae44dadd40684aa9c3a52516f35223188..794e38320f5685b2253b863bf7aa8e950784784f 100644 (file)
--- 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)