[PATCH v2 1/2] ACPI: CPPC: add paired FFH feedback-counter read hook
From: Pengjie Zhang <hidden>
Date: 2026-07-08 08:28:30
Also in:
linux-acpi, lkml
Subsystem:
acpi, acpi component architecture (acpica), the rest · Maintainers:
"Rafael J. Wysocki", Saket Dumbre, Linus Torvalds
cppc_get_perf_ctrs() reads the delivered and reference performance counters one at a time. Allow architectures to provide both FFH feedback counters in one operation when that either narrows the sampling window or avoids extra cross-CPU reads. Add a small FFH-specific hook for that case and fall back to the existing per-register reads when unsupported. Tested-by: Sumit Gupta <sumitg@nvidia.com> Reviewed-by: Sumit Gupta <sumitg@nvidia.com> Tested-by: Vanshidhar Konda <redacted> Reviewed-by: Vanshidhar Konda <redacted> Signed-off-by: Pengjie Zhang <redacted> --- drivers/acpi/cppc_acpi.c | 50 ++++++++++++++++++++++++++++++++++++---- include/acpi/cppc_acpi.h | 7 ++++++ 2 files changed, 52 insertions(+), 5 deletions(-)
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 9f572f481241..b6356476a46e 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c@@ -1004,6 +1004,22 @@ int __weak cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val) return -ENOTSUPP; } +/** + * cpc_read_ffh_fb_ctrs() - Read FFH feedback counters together + * @cpunum: Target CPU + * @reg1: first CPPC register information + * @val1: place holder for first return value + * @reg2: second CPPC register information + * @val2: place holder for second return value + * + * Return: 0 on success, error code otherwise + */ +int __weak cpc_read_ffh_fb_ctrs(int cpunum, struct cpc_reg *reg1, + u64 *val1, struct cpc_reg *reg2, u64 *val2) +{ + return -EOPNOTSUPP; +} + /** * cpc_write_ffh() - Write FFH register * @cpunum: CPU number to write
@@ -1496,6 +1512,33 @@ bool cppc_perf_ctrs_in_pcc_cpu(unsigned int cpu) } EXPORT_SYMBOL_GPL(cppc_perf_ctrs_in_pcc_cpu); +static int cppc_read_fb_ctrs(int cpunum, + struct cpc_register_resource *delivered_reg, + struct cpc_register_resource *reference_reg, + u64 *delivered, u64 *reference) +{ + int ret; + + /* + * For FFH feedback counters, try a paired read first to reduce + * sampling skew between delivered and reference counters. Fall + * back to the existing per-register reads if unsupported. + */ + if (CPC_IN_FFH(delivered_reg) && CPC_IN_FFH(reference_reg)) { + ret = cpc_read_ffh_fb_ctrs(cpunum, + &delivered_reg->cpc_entry.reg, delivered, + &reference_reg->cpc_entry.reg, reference); + if (ret != -EOPNOTSUPP) + return ret; + } + + ret = cpc_read(cpunum, delivered_reg, delivered); + if (ret) + return ret; + + return cpc_read(cpunum, reference_reg, reference); +} + /** * cppc_perf_ctrs_in_pcc - Check if any perf counters are in a PCC region. *
@@ -1561,11 +1604,8 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs) } } - ret = cpc_read(cpunum, delivered_reg, &delivered); - if (ret) - goto out_err; - - ret = cpc_read(cpunum, reference_reg, &reference); + ret = cppc_read_fb_ctrs(cpunum, delivered_reg, reference_reg, + &delivered, &reference); if (ret) goto out_err;
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index 8693890a7275..5acebe62feac 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h@@ -176,6 +176,8 @@ extern int cppc_get_transition_latency(int cpu); extern bool cpc_ffh_supported(void); extern bool cpc_supported_by_cpu(void); extern int cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val); +extern int cpc_read_ffh_fb_ctrs(int cpu, struct cpc_reg *reg1, u64 *val1, + struct cpc_reg *reg2, u64 *val2); extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val); extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf); extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable);
@@ -250,6 +252,11 @@ static inline int cpc_read_ffh(int cpunum, struct cpc_reg *reg, u64 *val) { return -EOPNOTSUPP; } +static inline int cpc_read_ffh_fb_ctrs(int cpu, struct cpc_reg *reg1, u64 *val1, + struct cpc_reg *reg2, u64 *val2) +{ + return -EOPNOTSUPP; +} static inline int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val) { return -EOPNOTSUPP;
--
2.33.0