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

[Shawn Lin]

On 2023/7/21 0:07, Manivannan Sadhasivam wrote:
> On Thu, Jul 20, 2023 at 10:37:36AM -0400, Frank Li wrote:
>> On Thu, Jul 20, 2023 at 07:55:09PM +0530, Manivannan Sadhasivam wrote:
>>> On Tue, Jul 18, 2023 at 03:34:26PM +0530, Manivannan Sadhasivam wrote:
>>>> On Mon, Jul 17, 2023 at 02:36:19PM -0400, Frank Li wrote:
>>>>> On Mon, Jul 17, 2023 at 10:15:26PM +0530, Manivannan Sadhasivam wrote:
>>>>>> On Wed, Apr 19, 2023 at 12:41:17PM -0400, Frank Li wrote:
>>>>>>> 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.
>>>>>>
>>>>>> AFAIK, typical workflow is to wait for PME_To_Ack.
>>>>>
>>>>> 1 Already wait for PME_to_ACK,  2, just wait for link actual enter L2.
>>>>> I think PCI RC needs some time to set link enter L2 after get ACK from
>>>>> PME.
>>>>>
>>>
>>> One more comment. If you transition the device to L2/L3, then it can loose power
>>> if Vaux was not provided. In that case, can all the devices work after resume?
>>> Most notably NVMe?
>>
>> I have not hardware to do such test, NVMe driver will reinit everything after
>> resume if no L1.1\L1.2 support. If there are L1.1\L1.2, NVME expect it leave
>> at L1.2 at suspend to get better resume latency.
>>
> 
> To be precise, NVMe driver will shutdown the device if there is no ASPM support
> and keep it in low power mode otherwise (there are other cases as well but we do
> not need to worry).
> 
> But here you are not checking for ASPM state in the suspend path, and just
> forcing the link to be in L2/L3 (thereby D3Cold) even though NVMe driver may
> expect it to be in low power state like ASPM/APST.
> 
> So you should only put the link to L2/L3 if there is no ASPM support. Otherwise,
> you'll ending up with bug reports when users connect NVMe to it.
> 


At this topic, it's very interesting to look at

drivers/pci/controller/dwc/pcie-tegra194.c


static int tegra_pcie_dw_suspend_noirq(struct device *dev)
{
         struct tegra_pcie_dw *pcie = dev_get_drvdata(dev);

         if (!pcie->link_state)
                 return 0;

         tegra_pcie_downstream_dev_to_D0(pcie);
         tegra_pcie_dw_pme_turnoff(pcie);
         tegra_pcie_unconfig_controller(pcie);

         return 0;
}

It brings back all the downstream components to D0, as I assumed it was 
L0 indeed, before sending PME aiming to enter L2.

> - Mani
> 
>> This API help remove duplicate codes and it can be improved gradually.
>>
>>
>>>
>>> - Mani
>>>
>>>
>>> -- 
>>> மணிவண்ணன் சதாசிவம்
>