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

[Mika Westerberg <mika.westerberg@linux.intel.com>]

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@linux.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().

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:

  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.