From 3f135a1d90678e2eb7155e4f1dff8974c4af5941 Mon Sep 17 00:00:00 2001
From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Date: Wed, 24 Aug 2022 19:32:21 +0200
Subject: drm: amd: amdgpu: ACPI: Add comment about ACPI_FADT_LOW_POWER_S0
Git-commit: 61ebd2fe6f793306ab6c05db8872931026dc1b8d
Patch-mainline: v6.1-rc1
References: jsc#PED-1166 jsc#PED-1168 jsc#PED-1170 jsc#PED-1218 jsc#PED-1220 jsc#PED-1222 jsc#PED-1223 jsc#PED-1225 jsc#PED-2849
According to the ACPI specification [1], the ACPI_FADT_LOW_POWER_S0
flag merely means that it is better to use low-power S0 idle on the
given platform than S3 (provided that the latter is supported) and it
doesn't preclude using either of them (which of them will be used
depends on the choices made by user space).
However, on some systems that flag is used to indicate whether or not
to enable special firmware mechanics allowing the system to save more
energy when suspended to idle. If that flag is unset, doing so is
generally risky.
Accordingly, add a comment to explain the ACPI_FADT_LOW_POWER_S0 check
in amdgpu_acpi_is_s0ix_active(), the purpose of which is otherwise
somewhat unclear.
Link: https://uefi.org/specs/ACPI/6.4/05_ACPI_Software_Programming_Model/ACPI_Software_Programming_Model.html#fixed-acpi-description-table-fadt # [1]
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
index 48bd660ddb85..7a801bdf47cc 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
@@ -1070,6 +1070,12 @@ bool amdgpu_acpi_is_s0ix_active(struct amdgpu_device *adev)
(pm_suspend_target_state != PM_SUSPEND_TO_IDLE))
return false;
+ /*
+ * If ACPI_FADT_LOW_POWER_S0 is not set in the FADT, it is generally
+ * risky to do any special firmware-related preparations for entering
+ * S0ix even though the system is suspending to idle, so return false
+ * in that case.
+ */
if (!(acpi_gbl_FADT.flags & ACPI_FADT_LOW_POWER_S0)) {
dev_warn_once(adev->dev,
"Power consumption will be higher as BIOS has not been configured for suspend-to-idle.\n"
--
2.38.1