linux-kernel - [PATCH] ACPI / LPIT: Register attributes based on FADT

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Date:   Fri, 28 Sep 2018 14:24:02 +0530
From:   Rajneesh Bhardwaj <rajneesh.bhardwaj@...ux.intel.com>
To:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     rjw@...ysocki.net, lenb@...nel.org, rajneesh.bhardwaj@...el.com,
        Rajneesh Bhardwaj <rajneesh.bhardwaj@...ux.intel.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject: [PATCH] ACPI / LPIT: Register attributes based on FADT

ACPI Low Power S0 Idle capabilities are announced via FADT table and can
be used to inform the kernel about the presence of one or more Low Power
Idle (LPI) entries as descried in LPIT table. LPIT table can exist
independently even if the FADT S0 Idle flag is not set and thus it could
confuse user since the following cpuidle attributes are created.

/sys/devices/system/cpu/cpuidle/low_power_idle_cpu_residency_us
/sys/devices/system/cpu/cpuidle/low_power_idle_system_residency_us

Presence or absence of above attributes could mean that the given
platform supports S0ix state or not.

This change allows to create the above cpuidle attributes only if
FADT table supports Low Power S0 Idle.

Cc: Rafael J . Wysocki <rafael.j.wysocki@...el.com>
Cc: Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@...ux.intel.com>
---
 drivers/acpi/acpi_lpit.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/acpi/acpi_lpit.c b/drivers/acpi/acpi_lpit.c
index cf4fc0161164..e43cb71b6972 100644
--- a/drivers/acpi/acpi_lpit.c
+++ b/drivers/acpi/acpi_lpit.c
@@ -117,11 +117,17 @@ static void lpit_update_residency(struct lpit_residency_info *info,
 		if (!info->iomem_addr)
 			return;
 
+		if (!(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0))
+			return;
+
 		/* Silently fail, if cpuidle attribute group is not present */
 		sysfs_add_file_to_group(&cpu_subsys.dev_root->kobj,
 					&dev_attr_low_power_idle_system_residency_us.attr,
 					"cpuidle");
 	} else if (info->gaddr.space_id == ACPI_ADR_SPACE_FIXED_HARDWARE) {
+		if (!(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0))
+			return;
+
 		/* Silently fail, if cpuidle attribute group is not present */
 		sysfs_add_file_to_group(&cpu_subsys.dev_root->kobj,
 					&dev_attr_low_power_idle_cpu_residency_us.attr,
-- 
2.17.1