[PATCH 2/3] 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: [email protected]
Suggested-by: Zhongqiu Han <[email protected]>
Reviewed-by: Zhongqiu Han <[email protected]>
Signed-off-by: Christian Loehle <[email protected]>
---
 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;
-- 
2.34.1