Re: [PATCH v6 4/9] ACPI: CPPC: Add cppc_get_perf() API to read performance controls
From: Sumit Gupta
Date: Tue Jan 27 2026 - 06:09:12 EST
As suggested at:On 2026/1/20 22:56, Sumit Gupta wrote:
Add cppc_get_perf() function to read values of performance controldesired_perf_reg is not an optional one, so it has to be supported.
registers including desired_perf, min_perf, max_perf, energy_perf,
and auto_sel.
This provides a read interface to complement the existing
cppc_set_perf() write interface for performance control registers.
Note that auto_sel is read by cppc_get_perf() but not written by
cppc_set_perf() to avoid unintended mode changes during performance
updates. It can be updated with existing dedicated cppc_set_auto_sel()
API.
Use cppc_get_perf() in cppc_cpufreq_get_cpu_data() to initialize
perf_ctrls with current hardware register values during cpufreq
policy initialization.
Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
---
drivers/acpi/cppc_acpi.c | 80
++++++++++++++++++++++++++++++++++
drivers/cpufreq/cppc_cpufreq.c | 6 +++
include/acpi/cppc_acpi.h | 5 +++
3 files changed, 91 insertions(+)
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index a09bdabaa804..de35aeb07833 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1739,6 +1739,86 @@ int cppc_set_enable(int cpu, bool enable)
}
EXPORT_SYMBOL_GPL(cppc_set_enable);
+/**
+ * cppc_get_perf - Get a CPU's performance controls.
+ * @cpu: CPU for which to get performance controls.
+ * @perf_ctrls: ptr to cppc_perf_ctrls. See cppc_acpi.h
+ *
+ * Return: 0 for success with perf_ctrls, -ERRNO otherwise.
+ */
+int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
+{
+ struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
+ struct cpc_register_resource *desired_perf_reg,
+ *min_perf_reg, *max_perf_reg,
+ *energy_perf_reg, *auto_sel_reg;
+ u64 desired_perf = 0, min = 0, max = 0, energy_perf = 0,
auto_sel = 0;
+ int pcc_ss_id = per_cpu(cpu_pcc_subspace_idx, cpu);
+ struct cppc_pcc_data *pcc_ss_data = NULL;
+ int ret = 0, regs_in_pcc = 0;
+
+ if (!cpc_desc) {
+ pr_debug("No CPC descriptor for CPU:%d\n", cpu);
+ return -ENODEV;
+ }
+
+ if (!perf_ctrls) {
+ pr_debug("Invalid perf_ctrls pointer\n");
+ return -EINVAL;
+ }
+
+ desired_perf_reg = &cpc_desc->cpc_regs[DESIRED_PERF];
+ min_perf_reg = &cpc_desc->cpc_regs[MIN_PERF];
+ max_perf_reg = &cpc_desc->cpc_regs[MAX_PERF];
+ energy_perf_reg = &cpc_desc->cpc_regs[ENERGY_PERF];
+ auto_sel_reg = &cpc_desc->cpc_regs[AUTO_SEL_ENABLE];
+
+ /* Are any of the regs PCC ?*/
+ if (CPC_IN_PCC(desired_perf_reg) || CPC_IN_PCC(min_perf_reg) ||
+ CPC_IN_PCC(max_perf_reg) || CPC_IN_PCC(energy_perf_reg) ||
+ CPC_IN_PCC(auto_sel_reg)) {
+ if (pcc_ss_id < 0) {
+ pr_debug("Invalid pcc_ss_id for CPU:%d\n", cpu);
+ return -ENODEV;
+ }
+ pcc_ss_data = pcc_data[pcc_ss_id];
+ regs_in_pcc = 1;
+ down_write(&pcc_ss_data->pcc_lock);
+ /* Ring doorbell once to update PCC subspace */
+ if (send_pcc_cmd(pcc_ss_id, CMD_READ) < 0) {
+ ret = -EIO;
+ goto out_err;
+ }
+ }
+
+ /* Read optional elements if present */
+ if (CPC_SUPPORTED(max_perf_reg))
+ cpc_read(cpu, max_perf_reg, &max);
+ perf_ctrls->max_perf = max;
+
+ if (CPC_SUPPORTED(min_perf_reg))
+ cpc_read(cpu, min_perf_reg, &min);
+ perf_ctrls->min_perf = min;
+
+ if (CPC_SUPPORTED(desired_perf_reg))
+ cpc_read(cpu, desired_perf_reg, &desired_perf);
+ perf_ctrls->desired_perf = desired_perf;
Please ignore my previous reply on this. Had some problem with my email
client and both mails got mixed.
The register is optional when Autonomous mode is enabled.
Seems the comment here is already resolved with Pierre's reply.
We discussed this during v4 [1] also.
[1]
https://lore.kernel.org/lkml/ccd45c1b-2f69-4725-918f-18063f00a864@xxxxxxxxxx/
Thank you,
Sumit Gupta
https://lore.kernel.org/all/5afea521-7d80-4e72-8809-77af60b0d957@xxxxxxx/
Maybe it would be useful to add a patch checking this:
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index e3796b520e473..7db74e19425e6 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -854,6 +854,12 @@ int acpi_cppc_processor_probe(struct acpi_processor
*pr)
}
per_cpu(cpu_pcc_subspace_idx, pr->id) = pcc_subspace_id;
+ if (!CPC_SUPPORTED(&cpc_ptr->cpc_regs[DESIRED_PERF]) &&
+ (!osc_sb_cppc2_support_acked ||
+ !CPC_SUPPORTED(&cpc_ptr->cpc_regs[AUTO_SEL_ENABLE])))
+ pr_warn("Desired perf. register is mandatory if CPPCV2
is not supported "
+ "or autonomous selection is disabled.\n");
+
/*
* Initialize the remaining cpc_regs as unsupported.
* Example: In case FW exposes CPPC v2, the below loop will
initialize
Thanks for the suggestion. I will add this as a separate patch in v7.
Thank you,
Sumit Gupta