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ACPI: CPPC: Skip desired_perf read in cppc_get_perf()

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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: 658fa7b1c4 ("ACPI: CPPC: Add cppc_get_perf() API to read performance controls")
Cc: stable@vger.kernel.org
Suggested-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>
Reviewed-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260803203531.1268651-3-christian.loehle@arm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
This commit is contained in:
Christian Loehle 2026-08-03 21:35:30 +01:00 committed by Rafael J. Wysocki
parent df5a1d4a8c
commit d3576424e8
1 changed files with 5 additions and 2 deletions
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7
drivers/acpi/cppc_acpi.c
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@ -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;