[PATCH v2 2/2] ACPI: processor idle: Check for architectural support for LPI

[Mario Limonciello]

When `osc_pc_lpi_support_confirmed` is set through `_OSC` and `_LPI` is
populated then the cpuidle driver assumes that LPI is fully functional.

However currently the kernel only provides architectural support for LPI
on ARM.  This leads to high power consumption on X86 platforms that
otherwise try to enable LPI.

So probe whether or not LPI support is implemented before enabling LPI in
the kernel.  This is done by overloading `acpi_processor_ffh_lpi_probe` to
check whether it returns `-EOPNOTSUPP`. It also means that all future
implementations of `acpi_processor_ffh_lpi_probe` will need to follow
these semantics as well.

Reviewed-by: Sudeep Holla <sudeep.holla at arm.com>
Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>
---
 drivers/acpi/processor_idle.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/acpi/processor_idle.c b/drivers/acpi/processor_idle.c
index f8e9fa82cb9b..32b20efff5f8 100644
--- a/drivers/acpi/processor_idle.c
+++ b/drivers/acpi/processor_idle.c
@@ -1080,6 +1080,11 @@ static int flatten_lpi_states(struct acpi_processor *pr,
 	return 0;
 }
 
+int __weak acpi_processor_ffh_lpi_probe(unsigned int cpu)
+{
+	return -EOPNOTSUPP;
+}
+
 static int acpi_processor_get_lpi_info(struct acpi_processor *pr)
 {
 	int ret, i;
@@ -1088,6 +1093,11 @@ static int acpi_processor_get_lpi_info(struct acpi_processor *pr)
 	struct acpi_device *d = NULL;
 	struct acpi_lpi_states_array info[2], *tmp, *prev, *curr;
 
+	/* make sure our architecture has support */
+	ret = acpi_processor_ffh_lpi_probe(pr->id);
+	if (ret == -EOPNOTSUPP)
+		return ret;
+
 	if (!osc_pc_lpi_support_confirmed)
 		return -EOPNOTSUPP;
 
@@ -1139,11 +1149,6 @@ static int acpi_processor_get_lpi_info(struct acpi_processor *pr)
 	return 0;
 }
 
-int __weak acpi_processor_ffh_lpi_probe(unsigned int cpu)
-{
-	return -ENODEV;
-}
-
 int __weak acpi_processor_ffh_lpi_enter(struct acpi_lpi_state *lpi)
 {
 	return -ENODEV;
-- 
2.34.1