PCI/portdrv: Only disable pciehp interrupts early when needed

Firmware developers reported that Linux issues two PCIe hotplug commands in
very short intervals on an ARM server, which doesn't comply with the PCIe
spec.  According to PCIe r6.1, sec 6.7.3.2, if the Command Completed event
is supported, software must wait for a command to complete or wait at
least 1 second before sending a new command.

In the failure case, the first PCIe hotplug command is from
get_port_device_capability(), which sends a command to disable PCIe hotplug
interrupts without waiting for its completion, and the second command comes
from pcie_enable_notification() of pciehp driver, which enables hotplug
interrupts again.

Fix this by only disabling the hotplug interrupts when the pciehp driver is
not enabled.

Link: https://lore.kernel.org/r/[email protected]
Fixes: 2bd50dd ("PCI: PCIe: Disable PCIe port services during port initialization")
Suggested-by: Lukas Wunner <[email protected]>
Signed-off-by: Feng Tang <[email protected]>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <[email protected]>
Reviewed-by: Lukas Wunner <[email protected]>
Reviewed-by: Kuppuswamy Sathyanarayanan <[email protected]>

Author: Feng Tang

drivers/pci/pcie/portdrv.c

@@ -228,10 +228,12 @@ static int get_port_device_capability(struct pci_dev *dev)
 
 		/*
 		 * Disable hot-plug interrupts in case they have been enabled
-		 * by the BIOS and the hot-plug service driver is not loaded.
+		 * by the BIOS and the hot-plug service driver won't be loaded
+		 * to handle them.
 		 */
-		pcie_capability_clear_word(dev, PCI_EXP_SLTCTL,
-			  PCI_EXP_SLTCTL_CCIE | PCI_EXP_SLTCTL_HPIE);
+		if (!IS_ENABLED(CONFIG_HOTPLUG_PCI_PCIE))
+			pcie_capability_clear_word(dev, PCI_EXP_SLTCTL,
+				PCI_EXP_SLTCTL_CCIE | PCI_EXP_SLTCTL_HPIE);
 	}
 
 #ifdef CONFIG_PCIEAER