As per ACPI specification "Guaranteed Performance Register" is a "Buffer"
field. It can't be "Integer" field. So treat "Integer" type as invalid and
ignore "Guaranteed Performance Register".
Also save one cpc_read() call, when "Guaranteed Performance Register" is
not present, which means register defined as:
"Register(SystemMemory, 0, 0, 0, 0)".
Fixes: 29523f095397 ("ACPI / CPPC: Add support for guaranteed performance")
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@xxxxxxxxxxxxxxx>
Cc: 4.20+ <stable@xxxxxxxxxxxxxxx> # 4.20+
---
drivers/acpi/cppc_acpi.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 1b207fca1420..3f6c290e06af 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1150,8 +1150,14 @@ 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_INTEGER ||
+ (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;
--
2.17.2
