linux-kernel - [BUG] Intel Apollolake: PCIe bridge "loses" capabilities after entering D3Cold state

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Message-ID: <CAFJ_xbq0cxcH-cgpXLU4Mjk30+muWyWm1aUZGK7iG53yaLBaQg@mail.gmail.com>
Date:   Fri, 21 Oct 2022 12:17:35 +0200
From:   Lukasz Majczak <lma@...ihalf.com>
To:     bhelgaas@...gle.com, Rajat Jain <rajatja@...gle.com>,
        Vidya Sagar <vidyas@...dia.com>
Cc:     upstream@...ihalf.com, linux-pci@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: [BUG] Intel Apollolake: PCIe bridge "loses" capabilities after
 entering D3Cold state

Hi,

This a follow-up from a discussion from “[PATCH V2] PCI/ASPM:
Save/restore L1SS Capability for suspend/resume”
(https://lore.kernel.org/lkml/d3228b1f-8d12-bfab-4cba-6d93a6869f20@nvidia.com/t/)

While working with Vidya’s patch I have noticed that after
suspend/resume cycle on my Chromebook (Apollolake) PCIe bridge loses
its capabilities - the missing part is:

Capabilities: [200 v1] L1 PM Substates
L1SubCap: PCI-PM_L1.2+ PCI-PM_L1.1+ ASPM_L1.2+ ASPM_L1.1+ L1_PM_Substates+
  PortCommonModeRestoreTime=40us PortTPowerOnTime=10us
L1SubCtl1: PCI-PM_L1.2+ PCI-PM_L1.1+ ASPM_L1.2+ ASPM_L1.1+
   T_CommonMode=40us LTR1.2_Threshold=98304ns
L1SubCtl2: T_PwrOn=60us

Digging more I’ve found out that entering D3Cold state causes this
issue (D3Hot seems to work fine).

With Vidya’s patch (all versions form V1 to V3) on upstream kernels
5.10/5.15  it was causing underlying device unavailable (in my case -
WiFi card) - the V4 (which was accepted and merged) works fine (I
guess thanks to “PCI/ASPM: Refactor L1 PM Substates Control Register
programming”) but the issue is still there - I mean now after
suspend/resume the underlying deceive works fine but mentioned
capabilities are still gone when using lspci -vvv.

I think with current code it does no harm to anyone, but just doing a
heads up about this.

Best regards,
Lukasz