[PATCHv2 3/3] ACPI: CPPC: Stop reading desired_perf in cppc_get_perf()

[Christian Loehle <christian.loehle@arm.com>]

cppc_get_perf() has one in-tree caller, cppc_cpufreq_get_cpu_data().
It uses the function to preserve existing controls before writing them, but
overwrites desired_perf with highest_perf before the first cppc_set_perf().
Consequently, the current Desired Performance value is not consumed.

Remove the Desired Performance read from this aggregate getter and
document that the field is returned as zero.

Signed-off-by: Christian Loehle <christian.loehle@arm.com>
---
 drivers/acpi/cppc_acpi.c | 23 ++++++++---------------
 1 file changed, 8 insertions(+), 15 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 210988d57b71..8ce2033ba993 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1828,22 +1828,22 @@ int cppc_set_enable(int cpu, bool enable)
 EXPORT_SYMBOL_GPL(cppc_set_enable);
 
 /**
- * cppc_get_perf - Get a CPU's performance controls.
+ * cppc_get_perf - Get a CPU's readable performance controls.
  * @cpu: CPU for which to get performance controls.
  * @perf_ctrls: ptr to cppc_perf_ctrls. See cppc_acpi.h
  *
+ * Desired Performance is not read and is returned as 0.
+ *
  * 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,
+	struct cpc_register_resource *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;
+	u64 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 = cppc_desired_perf_readable();
 	int ret = 0, regs_in_pcc = 0;
 
 	if (!cpc_desc) {
@@ -1856,16 +1856,14 @@ int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
 		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 ((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) ||
+	if (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);
@@ -1896,12 +1894,7 @@ int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
 	}
 	perf_ctrls->min_perf = min;
 
-	if (read_desired_perf && CPC_SUPPORTED(desired_perf_reg)) {
-		ret = cpc_read(cpu, desired_perf_reg, &desired_perf);
-		if (ret)
-			goto out_err;
-	}
-	perf_ctrls->desired_perf = desired_perf;
+	perf_ctrls->desired_perf = 0;
 
 	if (CPC_SUPPORTED(energy_perf_reg)) {
 		ret = cpc_read(cpu, energy_perf_reg, &energy_perf);
-- 
2.34.1