6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Christian Loehle [ 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. 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: stable@vger.kernel.org Suggested-by: Sumit Gupta Signed-off-by: Christian Loehle Link: https://patch.msgid.link/20260803203531.1268651-2-christian.loehle@arm.com Signed-off-by: Rafael J. Wysocki [ preserved the raw firmware revision while limiting parsing to the v3-sized register prefix ] Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- drivers/acpi/cppc_acpi.c | 13 +++++++++++-- drivers/cpufreq/cppc_cpufreq.c | 2 +- 2 files changed, 12 insertions(+), 3 deletions(-) --- a/drivers/acpi/cppc_acpi.c +++ b/drivers/acpi/cppc_acpi.c @@ -768,7 +768,6 @@ int acpi_cppc_processor_probe(struct acp } if (cpc_rev > CPPC_V3_REV) { num_ent = CPPC_V3_NUM_ENT; - cpc_rev = CPPC_V3_REV; } cpc_ptr->num_entries = num_ent; @@ -1289,10 +1288,20 @@ static int cppc_set_reg_val(int cpu, enu * @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_reg_val(cpunum, DESIRED_PERF, desired_perf); } EXPORT_SYMBOL_GPL(cppc_get_desired_perf); --- a/drivers/cpufreq/cppc_cpufreq.c +++ b/drivers/cpufreq/cppc_cpufreq.c @@ -766,7 +766,7 @@ out_invalid_counters: * 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);