Refer to PCIe r6.0, sec 5.2, fig 5-1 Link Power Management State Flow
Diagram. Both L0 and L2/L3 Ready can be transferred to LDn directly.

It's harmless to let dw_pcie_suspend_noirq() proceed suspend after the
PME_Turn_Off is sent out, whatever the LTSSM state is in L2 or L3 after
a recommended 10ms max wait refer to PCIe r6.0, sec 5.3.3.2.1 PME
Synchronization.

The LTSSM states of i.MX6QP PCIe is inaccessible after the PME_Turn_Off
is kicked off. To handle this case, don't poll L2 state and add one max
10ms delay if QUIRK_NOL2POLL_IN_PM flag is existing in suspend.

Main chenages in v2:
Add the following two patches.
- Skip PME_Turn_Off message if there is no endpoint connected.
- Don't return error when wait for link up.
v1:https://patchwork.kernel.org/project/linux-pci/cover/20250408065221.1941928-1-hongxing.zhu@nxp.com/

[PATCH v2 1/5] PCI: imx6: Don't poll LTSSM state of i.MX6QP PCIe in
[PATCH v2 2/5] PCI: imx6: Don't poll LTSSM state of i.MX7D PCIe in PM
[PATCH v2 3/5] PCI: dwc: Don't poll L2 if QUIRK_NOL2POLL_IN_PM is
[PATCH v2 4/5] PCI: dwc: Skip PME_Turn_Off message if there is no
[PATCH v2 5/5] PCI: dwc: Don't return error when wait for link up

drivers/pci/controller/dwc/pci-imx6.c             |  4 ++++
drivers/pci/controller/dwc/pcie-designware-host.c | 50 +++++++++++++++++++++++++++++++-------------------
drivers/pci/controller/dwc/pcie-designware.h      |  4 ++++
3 files changed, 39 insertions(+), 19 deletions(-)