PCI/EDR: Add edr_handle_event() comments

EDR documentation is a bit sketchy.  Add a couple comments to
edr_handle_event() about the devices involved.

Link: https://lore.kernel.org/r/20230407215259.GA3825733@bhelgaas
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

diff --git a/drivers/pci/pcie/edr.c b/drivers/pci/pcie/edr.c
index 87734e4..5f4914d 100644 (file)
--- a/drivers/pci/pcie/edr.c
+++ b/drivers/pci/pcie/edr.c
@@ -151,9 +151,18 @@ static void edr_handle_event(acpi_handle handle, u32 event, void *data)
        if (event != ACPI_NOTIFY_DISCONNECT_RECOVER)
                return;
 
+       /*
+        * pdev is a Root Port or Downstream Port that is still present and
+        * has triggered a containment event, e.g., DPC, so its child
+        * devices have been disconnected (ACPI r6.5, sec 5.6.6).
+        */
        pci_info(pdev, "EDR event received\n");
 
-       /* Locate the port which issued EDR event */
+       /*
+        * Locate the port that experienced the containment event.  pdev
+        * may be that port or a parent of it (PCI Firmware r3.3, sec
+        * 4.6.13).
+        */
        edev = acpi_dpc_port_get(pdev);
        if (!edev) {
                pci_err(pdev, "Firmware failed to locate DPC port\n");