Re: Thunderbolt, direct-complete and long suspend/resume time of Suspend-to-idle

[Kai-Heng Feng]

> On Mar 12, 2020, at 16:15, Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> wrote:
> 
> On Thu, Mar 12, 2020 at 12:41:08PM +0800, Kai-Heng Feng wrote:
>> 
>> 
>>> On Mar 11, 2020, at 18:38, Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> wrote:
>>> 
>>> On Wed, Mar 11, 2020 at 01:39:51PM +0800, Kai-Heng Feng wrote:
>>>> Hi,
>>>> 
>>>> I am currently investigating long suspend and resume time of suspend-to-idle.
>>>> It's because Thunderbolt bridges need to wait for 1100ms [1] for runtime-resume on system suspend, and also for system resume.
>>>> 
>>>> I made a quick hack to the USB driver and xHCI driver to support direct-complete, but I failed to do so for the parent PCIe bridge as it always disables the direct-complete [2], since device_may_wakeup() returns true for the device:
>>>> 
>>>> 	/* Avoid direct_complete to let wakeup_path propagate. */
>>>> 		if (device_may_wakeup(dev) || dev->power.wakeup_path)
>>>> 			dev->power.direct_complete = false;
>>> 
>>> You need to be careful here because otherwise you end up situation where
>>> the link is not properly trained and we tear down the whole tree of
>>> devices which is worse than waiting bit more for resume.
>> 
>> My idea is to direct-complete when there's no PCI or USB device
>> plugged into the TBT, and use pm_reuqest_resume() in complete() so it
>> won't block resume() or resume_noirq().
> 
> Before doing that..
> 
>>>> Once the direct-complete is disabled, system suspend/resume is used hence the delay in [1] is making the resume really slow. 
>>>> So how do we make suspend-to-idle faster? I have some ideas but I am not sure if they are feasible:
>>>> - Make PM core know the runtime_suspend() already use the same wakeup as suspend(), so it doesn't need to use device_may_wakeup() check to determine direct-complete.
>>>> - Remove the DPM_FLAG_NEVER_SKIP flag in pcieport driver, and use pm_request_resume() in its complete() callback to prevent blocking the resume process.
>>>> - Reduce the 1100ms delay. Maybe someone knows the values used in macOS and Windows...
>>> 
>>> Which system this is? ICL?
>> 
>> CML-H + Titan Ridge.
> 
> .. we should really understand this better because CML-H PCH root ports
> and Titan/Alpine Ridge downstream ports all support active link
> reporting so instead of the 1000+100ms you should see something like
> this:

Root port for discrete graphics:
# lspci -vvnn -s 00:01.0                    
00:01.0 PCI bridge [0604]: Intel Corporation Xeon E3-1200 v5/E3-1500 v5/6th Gen Core Processor PCIe Controller (x16) [8086:1901] (rev 02) (prog-if 00 [Normal decode])
        Capabilities: [a0] Express (v2) Root Port (Slot+), MSI 00
                LnkCap: Port #2, Speed 8GT/s, Width x16, ASPM L0s L1, Exit Latency L0s <256ns, L1 <8us
                        ClockPM- Surprise- LLActRep- BwNot+ ASPMOptComp+
                LnkCtl: ASPM L0s L1 Enabled; RCB 64 bytes Disabled- CommClk+
                        ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-
   
Thunderbolt ports:
# lspci -vvvv -s 04:00
04:00.0 PCI bridge [0604]: Intel Corporation JHL7540 Thunderbolt 3 Bridge [Titan Ridge 2C 2018] [8086:15e7] (rev 06) (prog-if 00 [Normal decode])
        Capabilities: [c0] Express (v2) Downstream Port (Slot+), MSI 00
                LnkCap: Port #0, Speed 2.5GT/s, Width x4, ASPM L1, Exit Latency L0s <64ns, L1 <1us
                        ClockPM- Surprise- LLActRep- BwNot+ ASPMOptComp+
                LnkCtl: ASPM L1 Enabled; Disabled- CommClk+
                        ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-

# lspci -vvnn -s 04:01
04:01.0 PCI bridge [0604]: Intel Corporation JHL7540 Thunderbolt 3 Bridge [Titan Ridge 2C 2018] [8086:15e7] (rev 06) (prog-if 00 [Normal decode])
        Capabilities: [c0] Express (v2) Downstream Port (Slot+), MSI 00
                LnkCap: Port #1, Speed 2.5GT/s, Width x4, ASPM L1, Exit Latency L0s <64ns, L1 <1us
                        ClockPM- Surprise- LLActRep+ BwNot+ ASPMOptComp+
                LnkCtl: ASPM L1 Enabled; Disabled- CommClk-
                        ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-

# lspci -vvnn -s 04:02 
04:02.0 PCI bridge [0604]: Intel Corporation JHL7540 Thunderbolt 3 Bridge [Titan Ridge 2C 2018] [8086:15e7] (rev 06) (prog-if 00 [Normal decode])
        Capabilities: [c0] Express (v2) Downstream Port (Slot+), MSI 00
                LnkCap: Port #2, Speed 2.5GT/s, Width x4, ASPM L1, Exit Latency L0s <64ns, L1 <1us
                        ClockPM- Surprise- LLActRep- BwNot+ ASPMOptComp+
                LnkCtl: ASPM L1 Enabled; Disabled- CommClk+
                        ExtSynch- ClockPM- AutWidDis- BWInt- AutBWInt-

So both CML-H PCH and TBT ports report "LLActRep-".

> 
>  1. Wait for the link + 100ms for the root port
>  2. Wait for the link + 100ms for the Titan Ridge downstream ports
>    (these are run paraller wrt all Titan Ridge downstream ports that have
>     something connected)
> 
> If there is a TBT device connected then 2. is repeated for it and so on.
> 
> So the 1000ms+ is really unexpected. Are you running mainline kernel and
> if so, can you share dmesg with CONFIG_PCI_DEBUG=y so we can see the
> delays there? Maybe also add some debugging to
> pcie_wait_for_link_delay() where it checks for the
> !pdev->link_active_reporting and waits for 1100ms.

I added the debug log in another thread and it does reach !pdev->link_active_reporting.

Let me see if patch link active reporting for the ports in PCI quirks can help.

Kai-Heng