[PATCH 3/3] e1000e: Serialize TGP e1000e PM ops

[Kai-Heng Feng]

On TGL systems, PCI_COMMAND may randomly flip to 0 on system resume.
This is devastating to drivers that use pci_set_master(), like NVMe and
xHCI, to enable DMA in their resume routine, as pci_set_master() can
inadvertently disable PCI_COMMAND_IO and PCI_COMMAND_MEMORY, making
resources inaccessible.

The issue is reproducible on all kernel releases, but the situation is
exacerbated by commit 6cecf02e77ab ("Revert "e1000e: disable s0ix entry
and exit flows for ME systems"").

Seems like ME can do many things to other PCI devices until it's finally out of
ULP polling. So ensure e1000e PM ops are serialized by enforcing suspend/resume
order to workaround the issue.

Of course this will make system suspend and resume a bit slower, but we
probably need to settle on this workaround until ME is fully supported.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212039
Signed-off-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
---
 drivers/net/ethernet/intel/e1000e/netdev.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
index e63445a8ce12..0244d3dd90a3 100644
--- a/drivers/net/ethernet/intel/e1000e/netdev.c
+++ b/drivers/net/ethernet/intel/e1000e/netdev.c
@@ -7319,7 +7319,8 @@ static const struct net_device_ops e1000e_netdev_ops = {
 
 static void e1000e_create_device_links(struct pci_dev *pdev)
 {
-	struct pci_dev *tgp_mei_me;
+	struct pci_bus *bus = pdev->bus;
+	struct pci_dev *tgp_mei_me, *p;
 
 	/* Find TGP mei_me devices and make e1000e power depend on mei_me */
 	tgp_mei_me = pci_get_device(PCI_VENDOR_ID_INTEL, 0xa0e0, NULL);
@@ -7335,6 +7336,17 @@ static void e1000e_create_device_links(struct pci_dev *pdev)
 		pci_info(pdev, "System and runtime PM depends on %s\n",
 			 pci_name(tgp_mei_me));
 
+	/* Find other devices in the SoC and make them depend on e1000e */
+	list_for_each_entry(p, &bus->devices, bus_list) {
+		if (&p->dev == &pdev->dev || &p->dev == &tgp_mei_me->dev)
+			continue;
+
+		if (device_link_add(&p->dev, &pdev->dev,
+				    DL_FLAG_AUTOREMOVE_SUPPLIER))
+			pci_info(p, "System PM depends on %s\n",
+				 pci_name(pdev));
+	}
+
 	pci_dev_put(tgp_mei_me);
 }
 
-- 
2.31.1