[bugzilla-daemon@bugzilla.kernel.org: [Bug 209361] New: PTMControl Enabled blocks Low Power Idle in 5% of s2idle attempts - Dell XPS-13 9300 Ice Lake]

[bugzilla-daemon@bugzilla.kernel.org: [Bug 209361] New: PTMControl Enabled blocks Low Power Idle in 5% of s2idle attempts - Dell XPS-13 9300 Ice Lake]

[Bjorn Helgaas]

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Date: Wed, 23 Sep 2020 15:22:47 +0000
From: bugzilla-daemon@bugzilla.kernel.org
To: bjorn@helgaas.com
Subject: [Bug 209361] New: PTMControl Enabled blocks Low Power Idle in 5% of
	s2idle attempts - Dell XPS-13 9300 Ice Lake
Message-ID: <bug-209361-41252@https.bugzilla.kernel.org/>

https://bugzilla.kernel.org/show_bug.cgi?id=209361

            Bug ID: 209361
           Summary: PTMControl Enabled blocks Low Power Idle in 5% of
                    s2idle attempts - Dell XPS-13 9300 Ice Lake
           Product: Drivers
           Version: 2.5
    Kernel Version: 5.9-rc5
          Hardware: All
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: PCI
          Assignee: drivers_pci@kernel-bugs.osdl.org
          Reporter: lenb@kernel.org
        Regression: No

System: Dell XPS-13 9300, Intel(R) Core(TM) i7-1065G7

Up through Linux 5.9-rc5, this system will typically get very good residency
in Low-Power-Idle upon s2idle.  But on 5% of attempts, it gets ZERO
residency in low-power-idle.

I have confirmed that this does not change if the time sleeping
is extended, or the time between experiments is extended.

David Box suggested disabling PTM.
Doing so resulted -- for the first time --
the system entering LPI on s2idle 100% of s2idle attempts
(770 attempts over 8 hours)

~/bin/pci_write8 0 0x1d 0 0x158 0
~/bin/pci_write8 0 0x1d 7 0x158 0

is what I used to disable PTM on my system
(write a 0, where pci_read8 previously showed the value 3)

This change is visible in the output of lspci as for both bridges:

< PTMControl: Enabled:+ RootSelected:+
> PTMControl: Enabled:- RootSelected:-

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