According to "PCIe r6.0, sec 5.5.4", add note about D0 requirement in
pci_enable_link_state() kernel-doc.

Signed-off-by: Jian-Hong Pan <jhp@endlessos.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
---
v3:
- Fix as readable comments

v4:
- The same

v5:
- Tweak and simplify the commit message

v6~10:
- The same

 drivers/pci/pcie/aspm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index cee2365e54b8..bd0a8a05647e 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -1442,6 +1442,9 @@ static int __pci_enable_link_state(struct pci_dev *pdev, int state, bool locked)
  * touch the LNKCTL register. Also note that this does not enable states
  * disabled by pci_disable_link_state(). Return 0 or a negative errno.
  *
+ * Note: Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
+ * PCIe r6.0, sec 5.5.4.
+ *
  * @pdev: PCI device
  * @state: Mask of ASPM link states to enable
  */
@@ -1458,6 +1461,9 @@ EXPORT_SYMBOL(pci_enable_link_state);
  * can't touch the LNKCTL register. Also note that this does not enable states
  * disabled by pci_disable_link_state(). Return 0 or a negative errno.
  *
+ * Note: Ensure devices are in D0 before enabling PCI-PM L1 PM Substates, per
+ * PCIe r6.0, sec 5.5.4.
+ *
  * @pdev: PCI device
  * @state: Mask of ASPM link states to enable
  *
-- 
2.46.2