[Nouveau] [PATCH v2] drm/nouveau/acpi: fix check for power resources support

[Peter Wu]

Check whether the kernel really supports power resources for a device,
otherwise the power might not be removed when the device is runtime
suspended (DSM should still work in these cases where PR does not).

This is a workaround for a problem where ACPICA and Windows 10 differ in
behavior. ACPICA does not correctly enumerate power resources within a
conditional block (due to delayed execution of such blocks) and as a
result power_resources is set to false even if _PR3 exists.

Fixes: 692a17dcc292 ("drm/nouveau/acpi: fix lockup with PCIe runtime PM")
Link: https://bugs.freedesktop.org/show_bug.cgi?id=98398
Reported-and-tested-by: Rick Kerkhof <rick.2889 at gmail.com>
Reviewed-by: Mika Westerberg <mika.westerberg at linux.intel.com>
Signed-off-by: Peter Wu <peter at lekensteyn.nl>
---
 v2: collected tags from Rick and Mika; added ACPICA note as requested by Mika

I suggest Cc: stable (if the maintainer is OK with that?)
---
 drivers/gpu/drm/nouveau/nouveau_acpi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_acpi.c b/drivers/gpu/drm/nouveau/nouveau_acpi.c
index dc57b62..193573d 100644
--- a/drivers/gpu/drm/nouveau/nouveau_acpi.c
+++ b/drivers/gpu/drm/nouveau/nouveau_acpi.c
@@ -240,7 +240,8 @@ static bool nouveau_pr3_present(struct pci_dev *pdev)
 	if (!parent_adev)
 		return false;
 
-	return acpi_has_method(parent_adev->handle, "_PR3");
+	return parent_adev->power.flags.power_resources &&
+		acpi_has_method(parent_adev->handle, "_PR3");
 }
 
 static void nouveau_dsm_pci_probe(struct pci_dev *pdev, acpi_handle *dhandle_out,
-- 
2.10.1