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

[Kai-Heng Feng]

> On Mar 12, 2020, at 18:41, Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx> wrote:
> 
> On Thu, Mar 12, 2020 at 06:10:45PM +0800, Kai-Heng Feng wrote:
>> 
>> 
>>> 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-
> 
> Interesting, Titan Ridge is connected to the graphics slot, no? What
> system this is?

No, TBT connects to another port, which supports link active reporting.
This is just to show not all CML-H ports support that.

> 
>> 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-
> 
> This one leads to the TBT NHI.
> 
>> # 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-
> 
> This one is one of the extension downstream ports and it supports active
> link reporting.
> 
>> # 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-
> 
> This one leads to the xHCI.
> 
>> So both CML-H PCH and TBT ports report "LLActRep-".
> 
> So in pci_bridge_wait_for_secondary_bus() we only call
> pcie_wait_for_link_delay() if the port supports speeds higher than 5
> GT/s (gen2). Now if I read the above correct all the ports except the
> root port support 2.5 GT/s (gen1) speeds so we should go to the
> msleep(delay) branch and not call pcie_wait_for_link_delay() at all:
> 
>        if (pcie_get_speed_cap(dev) <= PCIE_SPEED_5_0GT) {
>                pci_dbg(dev, "waiting %d ms for downstream link\n", delay);
>                msleep(delay);
>        } else {
>                pci_dbg(dev, "waiting %d ms for downstream link, after activation\n",
>                        delay);
>                if (!pcie_wait_for_link_delay(dev, true, delay)) {
>                        /* Did not train, no need to wait any further */
>                        return;
>                }
>        }
> 
> Only explanation I have is that delay itself is set to 1000ms for some
> reason. Can you check if that's the case and then maybe check where that
> delay is coming from?
> 
>>> 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.
> 
> Hmm, based on the above that should not happen :-(
> 
>> Let me see if patch link active reporting for the ports in PCI quirks can help.
> 
> Let's first investigate bit more to understand what is going on.
> 
> I suggest to create kernel.org bugzilla about this. Please include full
> dmesg and 'sudo lspci -vv' output at least and of course the steps you
> use to reproduce this.

https://bugzilla.kernel.org/show_bug.cgi?id=206837

Kai-Heng