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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Linux PM <linux-pm@vger.kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
 Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
 Xi Ruoyao <xry111@xry111.site>
Subject:
 [PATCH v1] cpufreq: intel_pstate: Check turbo_is_disabled() in
 store_no_turbo()
Date: Tue, 11 Jun 2024 16:53:06 +0200
Message-ID: <6061905.lOV4Wx5bFT@kreacher>
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From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

After recent changes in intel_pstate, global.turbo_disabled is only set
at the initialization time and never changed.  However, it turns out
that on some systems the "turbo disabled" bit in MSR_IA32_MISC_ENABLE,
the initial state of which is reflected by global.turbo_disabled, can be
flipped later and there should be a way to take that into account (other
than checking that MSR every time the driver runs which is costly and
useless overhead on the vast majority of systems).

For this purpose, notice that before the changes in question,
store_no_turbo() contained a turbo_is_disabled() check that was used
for updating global.turbo_disabled is the "turbo disabled" bit in
MSR_IA32_MISC_ENABLE had been flipped and that functionality can be
restored.  This way, users will be able to reset global.turbo_disabled
by writing 0 to no_turbo which used to work before.

This guarantees the driver state to remain in sync, but READ_ONCE()
annotations need to be added in two places where global.turbo_disabled
is accessed locklessly, so modify the driver to make that happen.

Fixes: 0940f1a8011f ("cpufreq: intel_pstate: Do not update global.turbo_disabled after initialization")
Closes: https://lore.kernel.org/linux-pm/bf3ebf1571a4788e97daf861eb493c12d42639a3.camel@xry111.site
Suggested-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Reported-by: Xi Ruoyao <xry111@xry111.site>
Tested-by: Xi Ruoyao <xry111@xry111.site>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpufreq/intel_pstate.c |   19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -1302,12 +1302,17 @@ static ssize_t store_no_turbo(struct kob
 
 	no_turbo = !!clamp_t(int, input, 0, 1);
 
-	if (no_turbo == global.no_turbo)
-		goto unlock_driver;
-
-	if (global.turbo_disabled) {
-		pr_notice_once("Turbo disabled by BIOS or unavailable on processor\n");
+	WRITE_ONCE(global.turbo_disabled, turbo_is_disabled());
+	if (global.turbo_disabled && !no_turbo) {
+		pr_notice("Turbo disabled by BIOS or unavailable on processor\n");
 		count = -EPERM;
+		if (global.no_turbo)
+			goto unlock_driver;
+		else
+			no_turbo = 1;
+	}
+
+	if (no_turbo == global.no_turbo) {
 		goto unlock_driver;
 	}
 
@@ -1762,7 +1767,7 @@ static u64 atom_get_val(struct cpudata *
 	u32 vid;
 
 	val = (u64)pstate << 8;
-	if (READ_ONCE(global.no_turbo) && !global.turbo_disabled)
+	if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled))
 		val |= (u64)1 << 32;
 
 	vid_fp = cpudata->vid.min + mul_fp(
@@ -1927,7 +1932,7 @@ static u64 core_get_val(struct cpudata *
 	u64 val;
 
 	val = (u64)pstate << 8;
-	if (READ_ONCE(global.no_turbo) && !global.turbo_disabled)
+	if (READ_ONCE(global.no_turbo) && !READ_ONCE(global.turbo_disabled))
 		val |= (u64)1 << 32;
 
 	return val;