FAILED: patch "[PATCH] ACPI: CPPC: Reject desired_perf reads on _CPC revision 4+" failed to apply to 6.6-stable tree

PATCH New [email protected] 2 participants 3 messages Sep 3 – Sep 8

Subsystems (5)

Stable branch ACPI CPU frequency scaling framework ACPI CPPC +1 more subsystems

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[email protected]

author maintainer

2026-09-03 14:05 UTC #0 lore raw

The patch below does not apply to the 6.6-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-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x df5a1d4a8cdfda20eb2581a85e81c7d436866534
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090308-padlock-setting-e1ac@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From df5a1d4a8cdfda20eb2581a85e81c7d436866534 Mon Sep 17 00:00:00 2001
From: Christian Loehle <[email protected]>
Date: Mon, 3 Aug 2026 21:35:29 +0100
Subject: [PATCH] ACPI: CPPC: Reject desired_perf reads on _CPC revision 4+

When CPPC feedback counters cannot provide a usable sample, cppc-cpufreq calls cppc_get_desired_perf() because some platforms repurpose Desired Performance to report actual delivered performance.

ACPI 6.5 defines _CPC revision 3 and lists Read/Write as the Optional Attribute of Desired Performance. ACPI 6.6 advances _CPC to revision 4 and lists only Write, so invoking that workaround for revision 4 or later would require a register read that the interface no longer specifies.

Make cppc_get_desired_perf() return -EOPNOTSUPP for _CPC revision 4 or later. Use the revision retained in the per-CPU CPC descriptor rather than the platform-wide FADT revision.

The _CPC revision may still not accurately describe the implemented register semantics. If a nominally revision 3 platform implements a non-readable Desired Performance register, a read may return zero and make cppc_cpufreq_get_rate() report 0 kHz. Treat a zero read as unusable and fall back to the cached OSPM request, just as for a failed read.

Fixes c47195631960 ("cppc_cpufreq: Use desired perf if feedback ctrs are 0 or unchanged")

Cc [email protected]

Signed-off-by Christian Loehle <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Rafael J. Wysocki <[email protected]>

drivers/acpi/cppc_acpi.c +16 -1

index 53d09ca98f06..42aeb749ebe0 100644
@@ -1316,15 +1316,30 @@ static int cppc_set_reg_val(int cpu, enum cppc_regs reg_idx, u64 val)
 	return cpc_write(cpu, reg, val);
 }
 
+static bool cppc_desired_perf_readable(const struct cpc_desc *cpc_desc)
+{
+	return cpc_desc->version < CPPC_V4_REV;
+}
+
 /**
  * cppc_get_desired_perf - Get the desired performance register value.
  * @cpunum: CPU from which to get desired performance.
  * @desired_perf: Return address.
  *
- * Return: 0 for success, -EIO otherwise.
+ * Return: 0 for success, -EOPNOTSUPP for _CPC revision 4 or later, and a
+ * negative errno otherwise.
  */
 int cppc_get_desired_perf(int cpunum, u64 *desired_perf)
 {
+	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
+
+	if (!cpc_desc)
+		return -ENODEV;
+
+	/* _CPC revision 4 no longer specifies Desired Performance as readable. */
+	if (!cppc_desired_perf_readable(cpc_desc))
+		return -EOPNOTSUPP;
+
 	return cppc_get_reg_val(cpunum, DESIRED_PERF, desired_perf);
 }
 EXPORT_SYMBOL_GPL(cppc_get_desired_perf);

drivers/cpufreq/cppc_cpufreq.c +1 -1

index 6fe0e972952a..80893844353c 100644
@@ -836,7 +836,7 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 	 * value first as some platforms may update the actual delivered perf
 	 * there; if failed, resort to the cached desired perf.
 	 */
-	if (cppc_get_desired_perf(cpu, &delivered_perf))
+	if (cppc_get_desired_perf(cpu, &delivered_perf) || !delivered_perf)
 		delivered_perf = cpu_data->perf_ctrls.desired_perf;
 
 	return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);

Sasha Levin

maintainer

2026-09-08 12:28 UTC #1 lore raw

PATCH 1/1 ACPI: CPPC: Reject desired_perf reads on _CPC revision 4+

From: Christian Loehle <[email protected]>

[ Upstream commit df5a1d4a8cdfda20eb2581a85e81c7d436866534 ]

When CPPC feedback counters cannot provide a usable sample, cppc-cpufreq calls cppc_get_desired_perf() because some platforms repurpose Desired Performance to report actual delivered performance.

Make cppc_get_desired_perf() return -EOPNOTSUPP for _CPC revision 4 or later. Use the revision retained in the per-CPU CPC descriptor rather than the platform-wide FADT revision.

Fixes c47195631960 ("cppc_cpufreq: Use desired perf if feedback ctrs are 0 or unchanged")

Cc [email protected]

Signed-off-by Christian Loehle <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Rafael J. Wysocki <[email protected]>

[ preserved the original CPPC revision while parsing only the supported v3 prefix and retaining cppc_get_perf() ]

Signed-off-by Sasha Levin <[email protected]>

---
 drivers/acpi/cppc_acpi.c       | 13 +++++++++++--
 drivers/cpufreq/cppc_cpufreq.c |  2 +-
 2 files changed, 12 insertions(+), 3 deletions(-)

drivers/acpi/cppc_acpi.c +11 -2

index 33b3e6dd17c58..c9ae5ea408a04 100644
@@ -764,7 +764,6 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
 	}
 	if (cpc_rev > CPPC_V3_REV) {
 		num_ent = CPPC_V3_NUM_ENT;
-		cpc_rev = CPPC_V3_REV;
 	}
 
 	cpc_ptr->num_entries = num_ent;

@@ -1222,10 +1221,20 @@ static int cppc_get_perf(int cpunum, enum cppc_regs reg_idx, u64 *perf)
  * @cpunum: CPU from which to get desired performance.
  * @desired_perf: Return address.
  *
- * Return: 0 for success, -EIO otherwise.
+ * Return: 0 for success, -EOPNOTSUPP for _CPC revision 4 or later, and a
+ * negative errno otherwise.
  */
 int cppc_get_desired_perf(int cpunum, u64 *desired_perf)
 {
+	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
+
+	if (!cpc_desc)
+		return -ENODEV;
+
+	/* _CPC revision 4 no longer specifies Desired Performance as readable. */
+	if (cpc_desc->version > CPPC_V3_REV)
+		return -EOPNOTSUPP;
+
 	return cppc_get_perf(cpunum, DESIRED_PERF, desired_perf);
 }
 EXPORT_SYMBOL_GPL(cppc_get_desired_perf);

drivers/cpufreq/cppc_cpufreq.c +1 -1

index 4d96eed64fe0c..5a5832a2f9b2a 100644
@@ -813,7 +813,7 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 	 * value first as some platforms may update the actual delivered perf
 	 * there; if failed, resort to the cached desired perf.
 	 */
-	if (cppc_get_desired_perf(cpu, &delivered_perf))
+	if (cppc_get_desired_perf(cpu, &delivered_perf) || !delivered_perf)
 		delivered_perf = cpu_data->perf_ctrls.desired_perf;
 
 	return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);

Signature · 1 line

2.53.0

Sasha Levin

maintainer

2026-09-08 12:28 UTC #2 lore raw

PATCH 1/1 ACPI: CPPC: Reject desired_perf reads on _CPC revision 4+

In reply to [email protected]

From: Christian Loehle <[email protected]>

[ Upstream commit df5a1d4a8cdfda20eb2581a85e81c7d436866534 ]

When CPPC feedback counters cannot provide a usable sample, cppc-cpufreq calls cppc_get_desired_perf() because some platforms repurpose Desired Performance to report actual delivered performance.

Make cppc_get_desired_perf() return -EOPNOTSUPP for _CPC revision 4 or later. Use the revision retained in the per-CPU CPC descriptor rather than the platform-wide FADT revision.

Fixes c47195631960 ("cppc_cpufreq: Use desired perf if feedback ctrs are 0 or unchanged")

Cc [email protected]

Signed-off-by Christian Loehle <[email protected]>

Link https://patch.msgid.link/[email protected] open here

Signed-off-by Rafael J. Wysocki <[email protected]>

[ preserved the original CPPC revision while parsing only the supported v3 prefix and retaining cppc_get_perf() ]

Signed-off-by Sasha Levin <[email protected]>

---
 drivers/acpi/cppc_acpi.c       | 13 +++++++++++--
 drivers/cpufreq/cppc_cpufreq.c |  2 +-
 2 files changed, 12 insertions(+), 3 deletions(-)

drivers/acpi/cppc_acpi.c +11 -2

index 33b3e6dd17c58..c9ae5ea408a04 100644
@@ -764,7 +764,6 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
 	}
 	if (cpc_rev > CPPC_V3_REV) {
 		num_ent = CPPC_V3_NUM_ENT;
-		cpc_rev = CPPC_V3_REV;
 	}
 
 	cpc_ptr->num_entries = num_ent;

@@ -1222,10 +1221,20 @@ static int cppc_get_perf(int cpunum, enum cppc_regs reg_idx, u64 *perf)
  * @cpunum: CPU from which to get desired performance.
  * @desired_perf: Return address.
  *
- * Return: 0 for success, -EIO otherwise.
+ * Return: 0 for success, -EOPNOTSUPP for _CPC revision 4 or later, and a
+ * negative errno otherwise.
  */
 int cppc_get_desired_perf(int cpunum, u64 *desired_perf)
 {
+	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
+
+	if (!cpc_desc)
+		return -ENODEV;
+
+	/* _CPC revision 4 no longer specifies Desired Performance as readable. */
+	if (cpc_desc->version > CPPC_V3_REV)
+		return -EOPNOTSUPP;
+
 	return cppc_get_perf(cpunum, DESIRED_PERF, desired_perf);
 }
 EXPORT_SYMBOL_GPL(cppc_get_desired_perf);

drivers/cpufreq/cppc_cpufreq.c +1 -1

index 4d96eed64fe0c..5a5832a2f9b2a 100644
@@ -813,7 +813,7 @@ static unsigned int cppc_cpufreq_get_rate(unsigned int cpu)
 	 * value first as some platforms may update the actual delivered perf
 	 * there; if failed, resort to the cached desired perf.
 	 */
-	if (cppc_get_desired_perf(cpu, &delivered_perf))
+	if (cppc_get_desired_perf(cpu, &delivered_perf) || !delivered_perf)
 		delivered_perf = cpu_data->perf_ctrls.desired_perf;
 
 	return cppc_perf_to_khz(&cpu_data->perf_caps, delivered_perf);

Signature · 1 line

2.53.0