linux-kernel - [PATCH v2 1/2] ACPI / CPPC: Fix processing for guaranteed performance

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Date:   Mon, 25 Mar 2019 09:04:39 -0700
From:   Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
To:     rjw@...ysocki.net, lenb@...nel.org, viresh.kumar@...aro.org
Cc:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, pprakash@...eaurora.org,
        wangxiongfeng2@...wei.com, srinivas.pandruvada@...ux.intel.com
Subject: [PATCH v2 1/2] ACPI / CPPC: Fix processing for guaranteed performance

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")
Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc: 4.20+ <stable@...r.kernel.org> # 4.20+
---
 drivers/acpi/cppc_acpi.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 1b207fca1420..d4244e7d0e38 100644
--- 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;
-- 
2.17.2