ACPI / CPPC: Fix guaranteed performance handling

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: 29523f095397 ("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
index 1b207fca1420bbc5c40469e1b3558cb38a57c450..d4244e7d0e38f05cef4e5b97df55d3a9946837c1 100644 (file)
--- 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;