[PATCH 4.17 284/336] PCI/ASPM: Disable ASPM L1.2 Substate if we dont have LTR

[Greg Kroah-Hartman]

4.17-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

[ Upstream commit 9ab105deb60fa76d66cae5548819b4e8703d2056 ]

When in the ASPM L1.0 state (but not the PCI-PM L1.0 state), the most
recent LTR value and the LTR_L1.2_THRESHOLD determines whether the link
enters the L1.2 substate.

If we don't have LTR enabled, prevent the use of ASPM L1.2.

PCI-PM L1.2 may still be used because it doesn't depend on
LTR_L1.2_THRESHOLD (see PCIe r4.0, sec 5.5.1).

Tested-by: Srinath Mannam <srinath.mannam@xxxxxxxxxxxx>
Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/pci/pcie/aspm.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -400,6 +400,15 @@ static void pcie_get_aspm_reg(struct pci
 		info->l1ss_cap = 0;
 		return;
 	}
+
+	/*
+	 * If we don't have LTR for the entire path from the Root Complex
+	 * to this device, we can't use ASPM L1.2 because it relies on the
+	 * LTR_L1.2_THRESHOLD.  See PCIe r4.0, secs 5.5.4, 6.18.
+	 */
+	if (!pdev->ltr_path)
+		info->l1ss_cap &= ~PCI_L1SS_CAP_ASPM_L1_2;
+
 	pci_read_config_dword(pdev, info->l1ss_cap_ptr + PCI_L1SS_CTL1,
 			      &info->l1ss_ctl1);
 	pci_read_config_dword(pdev, info->l1ss_cap_ptr + PCI_L1SS_CTL2,