PCI/ASPM: Allow ASPM on links to PCIe-to-PCI/PCI-X Bridges

7d715a6 ("PCI: add PCI Express ASPM support") added the ability for
Linux to enable ASPM, but for some undocumented reason, it didn't enable
ASPM on links where the downstream component is a PCIe-to-PCI/PCI-X Bridge.

Remove this exclusion so we can enable ASPM on these links.

The Dell OptiPlex 7080 mentioned in the bugzilla has a TI XIO2001
PCIe-to-PCI Bridge.  Enabling ASPM on the link leading to it allows the
Intel SoC to enter deeper Package C-states, which is a significant power
savings.

[bhelgaas: commit log]
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=207571
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Kai-Heng Feng <[email protected]>
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Mika Westerberg <[email protected]>

drivers/pci/pcie/aspm.c

@@ -628,16 +628,6 @@ static void pcie_aspm_cap_init(struct pcie_link_state *link, int blacklist)
 
 	/* Setup initial capable state. Will be updated later */
 	link->aspm_capable = link->aspm_support;
-	/*
-	 * If the downstream component has pci bridge function, don't
-	 * do ASPM for now.
-	 */
-	list_for_each_entry(child, &linkbus->devices, bus_list) {
-		if (pci_pcie_type(child) == PCI_EXP_TYPE_PCI_BRIDGE) {
-			link->aspm_disable = ASPM_STATE_ALL;
-			break;
-		}
-	}
 
 	/* Get and check endpoint acceptable latencies */
 	list_for_each_entry(child, &linkbus->devices, bus_list) {