drm/radeon: fix power state when port pm is unavailable (v2)

When PCIe port PM is not enabled (system BIOS is pre-2015 or the
pcie_port_pm=off parameter is set), legacy ATPX PM should still be
marked as supported. Otherwise the GPU can fail to power on after
runtime suspend. This affected a Dell Inspiron 5548.

Ideally the BIOS date in the PCI core is lowered to 2013 (the first year
where hybrid graphics platforms using power resources was introduced),
but that seems more risky at this point and would not solve the
pcie_port_pm=off issue.

v2: agd: fix typo

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98505
Signed-off-by: Peter Wu <peter@lekensteyn.nl>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: <stable@vger.kernel.org> # 4.8+
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_atpx_handler.c

@@ -34,6 +34,7 @@ struct radeon_atpx {
 
 static struct radeon_atpx_priv {
 	bool atpx_detected;
+	bool bridge_pm_usable;
 	/* handle for device - and atpx */
 	acpi_handle dhandle;
 	struct radeon_atpx atpx;
@@ -203,7 +204,11 @@ static int radeon_atpx_validate(struct radeon_atpx *atpx)
 	atpx->is_hybrid = false;
 	if (valid_bits & ATPX_MS_HYBRID_GFX_SUPPORTED) {
 		printk("ATPX Hybrid Graphics\n");
-		atpx->functions.power_cntl = false;
+		/*
+		 * Disable legacy PM methods only when pcie port PM is usable,
+		 * otherwise the device might fail to power off or power on.
+		 */
+		atpx->functions.power_cntl = !radeon_atpx_priv.bridge_pm_usable;
 		atpx->is_hybrid = true;
 	}
 
@@ -474,6 +479,7 @@ static int radeon_atpx_power_state(enum vga_switcheroo_client_id id,
  */
 static bool radeon_atpx_pci_probe_handle(struct pci_dev *pdev)
 {
+	struct pci_dev *parent_pdev = pci_upstream_bridge(pdev);
 	acpi_handle dhandle, atpx_handle;
 	acpi_status status;
 
@@ -487,6 +493,7 @@ static bool radeon_atpx_pci_probe_handle(struct pci_dev *pdev)
 
 	radeon_atpx_priv.dhandle = dhandle;
 	radeon_atpx_priv.atpx.handle = atpx_handle;
+	radeon_atpx_priv.bridge_pm_usable = parent_pdev && parent_pdev->bridge_d3;
 	return true;
 }