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

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Date:   Thu, 12 Mar 2020 12:41:08 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Rafael Wysocki <rafael.j.wysocki@...el.com>,
        "Shih-Yuan Lee (FourDollars)" <sylee@...onical.com>,
        Tiffany <tiffany.wang@...onical.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: Thunderbolt, direct-complete and long suspend/resume time of
 Suspend-to-idle



> On Mar 11, 2020, at 18:38, Mika Westerberg <mika.westerberg@...ux.intel.com> 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().

> 
>> 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.

> I think it is the TBT root ports only that do
> not support active link reporting. The PCIe spec is not entirely clear
> about root ports since it explictly mentions only downstream ports so
> one option would be to check for root port and that it supports gen 3
> speeds and based on that wait for max say 2 * 100ms or something like
> that.

So 200ms for rootport, but still 1100ms for downstream ports?

Kai-Heng