PCI: pciehp: Obey compulsory command delay after resume

This change “PCI: pciehp: Obey compulsory command delay after resume” in Linux kernel is authored by Lukas Wunner <lukas [at] wunner.de> on Thu Jul 19 17:27:54 2018 -0500.

PCI: pciehp: Obey compulsory command delay after resume

Upon resume from system sleep, the Slot Control register is written via:

  pci_pm_resume_noirq()
    pci_pm_default_resume_early()
      pci_restore_state()
        pci_restore_pcie_state()

PCIe r4.0, sec 6.7.3.2 says that after "issuing a write transaction that
targets any portion of the Port's Slot Control register, [...] software
must wait for [the] command to complete before issuing the next command".

pciehp currently fails to enforce that rule after the above-mentioned
write.  Fix it.

(Moving restoration of the Slot Control register to pciehp doesn't seem
to make sense because the other PCIe hotplug drivers may need it as
well.)

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit 469e764.

There are 4 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/pci/hotplug/pciehp_core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
index a5bd3b0..3e73b12 100644
--- a/drivers/pci/hotplug/pciehp_core.c
+++ b/drivers/pci/hotplug/pciehp_core.c
@@ -284,6 +284,10 @@ static int pciehp_resume_noirq(struct pcie_device *dev)
 	struct controller *ctrl = get_service_data(dev);
 	struct slot *slot = ctrl->slot;
 
+	/* pci_restore_state() just wrote to the Slot Control register */
+	ctrl->cmd_started = jiffies;
+	ctrl->cmd_busy = true;
+
 	/* clear spurious events from rediscovery of inserted card */
 	if (slot->state == ON_STATE || slot->state == BLINKINGOFF_STATE)
 		pcie_clear_hotplug_events(ctrl);

The commit for this change in Linux stable tree is 469e764 (patch).

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