ACPI / CPPC: Fix guaranteed performance handling

spandruvada · rafaeljw · commit edef1ef13418 · 2019-03-25T23:57:21.000+01:00
As per the ACPI specification, "Guaranteed Performance Register" is a "Buffer" field and it cannot be "Integer", so treat the "Integer" type for "Guaranteed Performance Register" field as invalid and ignore its value in that case. Also save one cpc_read() call when "Guaranteed Performance Register" is not present, which means a register defined as: "Register(SystemMemory, 0, 0, 0, 0)". Fixes: 29523f0 ("ACPI / CPPC: Add support for guaranteed performance") Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com> Cc: 4.20+ <stable@vger.kernel.org> # 4.20+ Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
@@ -1150,8 +1150,13 @@ int cppc_get_perf_caps(int cpunum, struct cppc_perf_caps *perf_caps)
 	cpc_read(cpunum, nominal_reg, &nom);
 	perf_caps->nominal_perf = nom;
 
-	cpc_read(cpunum, guaranteed_reg, &guaranteed);
-	perf_caps->guaranteed_perf = guaranteed;
+	if (guaranteed_reg->type != ACPI_TYPE_BUFFER  ||
+	    IS_NULL_REG(&guaranteed_reg->cpc_entry.reg)) {
+		perf_caps->guaranteed_perf = 0;
+	} else {
+		cpc_read(cpunum, guaranteed_reg, &guaranteed);
+		perf_caps->guaranteed_perf = guaranteed;
+	}
 
 	cpc_read(cpunum, lowest_non_linear_reg, &min_nonlinear);
 	perf_caps->lowest_nonlinear_perf = min_nonlinear;
