[PATCH v3 1/2] PCI: dwc: Implement general suspend/resume functionality for L2/L3 transitions

[Frank Li]

> 
> Introduced helper function dw_pcie_get_ltssm to retrieve
> SMLH_LTSS_STATE.
> Added API pme_turn_off and exit_from_l2 for managing L2/L3 state
> transitions.
> 
> Typical L2 entry workflow:
> 
> 1. Transmit PME turn off signal to PCI devices.
> 2. Await link entering L2_IDLE state.
> 3. Transition Root complex to D3 state.
> 
> Typical L2 exit workflow:
> 
> 1. Transition Root complex to D0 state.
> 2. Issue exit from L2 command.
> 3. Reinitialize PCI host.
> 4. Wait for link to become active.
> 
> Signed-off-by: Frank Li <Frank.Li at nxp.com>
> ---

Ping

> Change from v2 to v3:
> - Basic rewrite whole patch according rob herry suggestion.
>   put common function into dwc, so more soc can share the same logic.
>