From d3576424e8fa702a15a1963718a07eb672db9be7 Mon Sep 17 00:00:00 2001 From: Christian Loehle Date: Mon, 3 Aug 2026 21:35:30 +0100 Subject: ACPI: CPPC: Skip desired_perf read in cppc_get_perf() 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. cppc_get_perf() nevertheless reads the register when initializing performance controls, even though cppc-cpufreq overwrites the value before using it. Use the _CPC revision check from cppc_get_desired_perf() and leave desired_perf zero instead of reading it for _CPC revision 4 or later. Also exclude the register from PCC read-command detection so it cannot trigger an otherwise unnecessary read command. Fixes: 658fa7b1c47a ("ACPI: CPPC: Add cppc_get_perf() API to read performance controls") Cc: stable@vger.kernel.org Suggested-by: Zhongqiu Han Reviewed-by: Zhongqiu Han Signed-off-by: Christian Loehle Link: https://patch.msgid.link/20260803203531.1268651-3-christian.loehle@arm.com Signed-off-by: Rafael J. Wysocki --- drivers/acpi/cppc_acpi.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c index 42aeb749ebe0..becb7e442b30 100644 --- a/drivers/acpi/cppc_acpi.c +++ b/drivers/acpi/cppc_acpi.c @@ -1845,12 +1845,14 @@ int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls) 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; + bool read_desired_perf; int ret = 0, regs_in_pcc = 0; if (!cpc_desc) { pr_debug("No CPC descriptor for CPU:%d\n", cpu); return -ENODEV; } + read_desired_perf = cppc_desired_perf_readable(cpc_desc); if (!perf_ctrls) { pr_debug("Invalid perf_ctrls pointer\n"); @@ -1864,7 +1866,8 @@ int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls) 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) || + if ((read_desired_perf && 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) { @@ -1896,7 +1899,7 @@ int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls) } perf_ctrls->min_perf = min; - if (CPC_SUPPORTED(desired_perf_reg)) { + if (read_desired_perf && CPC_SUPPORTED(desired_perf_reg)) { ret = cpc_read(cpu, desired_perf_reg, &desired_perf); if (ret) goto out_err; -- cgit v1.2.3