ACPI / CPPC: acquire pcc_lock only while accessing PCC subspace

We need to acquire pcc_lock only when we are accessing registers
that are in the PCC subspsace.
Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/cppc_acpi.c

@@ -763,7 +763,7 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
 	struct cpc_register_resource *highest_reg, *lowest_reg, *ref_perf,
 								 *nom_perf;
 	u64 high, low, ref, nom;
-	int ret = 0;
+	int ret = 0, regs_in_pcc = 0;
 
 	if (!cpc_desc) {
 		pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
@@ -775,13 +775,13 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
 	ref_perf = &cpc_desc->cpc_regs[REFERENCE_PERF];
 	nom_perf = &cpc_desc->cpc_regs[NOMINAL_PERF];
 
-	spin_lock(&pcc_lock);
-
 	/* Are any of the regs PCC ?*/
 	if ((highest_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
-			(lowest_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
-			(ref_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
-			(nom_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)) {
+		(lowest_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
+		(ref_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
+		(nom_perf->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)) {
+		spin_lock(&pcc_lock);
+		regs_in_pcc = 1;
 		/* Ring doorbell once to update PCC subspace */
 		if (send_pcc_cmd(CMD_READ) < 0) {
 			ret = -EIO;
@@ -808,7 +808,8 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
 		ret = -EFAULT;
 
 out_err:
-	spin_unlock(&pcc_lock);
+	if (regs_in_pcc)
+		spin_unlock(&pcc_lock);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(cppc_get_perf_caps);
@@ -825,7 +826,7 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
 	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
 	struct cpc_register_resource *delivered_reg, *reference_reg;
 	u64 delivered, reference;
-	int ret = 0;
+	int ret = 0, regs_in_pcc = 0;
 
 	if (!cpc_desc) {
 		pr_debug("No CPC descriptor for CPU:%d\n", cpunum);
@@ -835,11 +836,11 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
 	delivered_reg = &cpc_desc->cpc_regs[DELIVERED_CTR];
 	reference_reg = &cpc_desc->cpc_regs[REFERENCE_CTR];
 
-	spin_lock(&pcc_lock);
-
 	/* Are any of the regs PCC ?*/
 	if ((delivered_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) ||
 		(reference_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)) {
+		spin_lock(&pcc_lock);
+		regs_in_pcc = 1;
 		/* Ring doorbell once to update PCC subspace */
 		if (send_pcc_cmd(CMD_READ) < 0) {
 			ret = -EIO;
@@ -865,7 +866,8 @@ int cppc_get_perf_ctrs(int cpunum, struct cppc_perf_fb_ctrs *perf_fb_ctrs)
 	perf_fb_ctrs->prev_reference = reference;
 
 out_err:
-	spin_unlock(&pcc_lock);
+	if (regs_in_pcc)
+		spin_unlock(&pcc_lock);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(cppc_get_perf_ctrs);
@@ -890,10 +892,9 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
 
 	desired_reg = &cpc_desc->cpc_regs[DESIRED_PERF];
 
-	spin_lock(&pcc_lock);
-
 	/* If this is PCC reg, check if channel is free before writing */
 	if (desired_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM) {
+		spin_lock(&pcc_lock);
 		ret = check_pcc_chan();
 		if (ret)
 			goto busy_channel;
@@ -912,7 +913,8 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
 			ret = -EIO;
 	}
 busy_channel:
-	spin_unlock(&pcc_lock);
+	if (desired_reg->cpc_entry.reg.space_id == ACPI_ADR_SPACE_PLATFORM_COMM)
+		spin_unlock(&pcc_lock);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(cppc_set_perf);