linux-kernel - Re: [PATCH V2] PCI/ASPM: Save/restore L1SS Capability for suspend/resume

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Date:   Thu, 25 Aug 2022 18:01:21 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
Cc:     Vidya Sagar <vidyas@...dia.com>, Lukasz Majczak <lma@...ihalf.com>,
        Rajat Jain <rajatja@...gle.com>,
        Ben Chuang <benchuanggli@...il.com>, bhelgaas@...gle.com,
        lorenzo.pieralisi@....com, refactormyself@...il.com, kw@...ux.com,
        kenny@...ix.com, treding@...dia.com, jonathanh@...dia.com,
        abhsahu@...dia.com, sagupta@...dia.com, linux-pci@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kthota@...dia.com, mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V2] PCI/ASPM: Save/restore L1SS Capability for
 suspend/resume

On Tue, Aug 23, 2022 at 10:55:01PM +0800, Kai-Heng Feng wrote:
> On Tue, Aug 9, 2022 at 12:17 AM Vidya Sagar <vidyas@...dia.com> wrote:
> >
> > Thanks Lukasz for the update.
> > I think confirms that there is no issue with the patch as such.
> > Bjorn, could you please define the next step for this patch?
> 
> I think the L1SS cap went away _after_ L1SS registers are restored,
> since your patch already check the cap before doing any write:
> +       aspm_l1ss = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_L1SS);
> +       if (!aspm_l1ss)
> +               return;
> 
> That means it's more likely to be caused by the following change:
> +       pci_write_config_dword(dev, aspm_l1ss + PCI_L1SS_CTL2, *cap++);
> +       pci_write_config_dword(dev, aspm_l1ss + PCI_L1SS_CTL1, *cap++);
> 
> So is it possible to clear PCI_L1SS_CTL1 before setting PCI_L1SS_CTL2,
> like what aspm_calc_l1ss_info() does?

Sorry, I've totally lost track of where we are with this.  I guess the
object is to save/restore L1SS state.

And there are two problems that aren't understood yet?

  1) Lukasz's 01:00.0 wifi device didn't work immediately after
  resume, but seemed to be hot-added later? [1]

  2) The 00:14.0 Root Port L1SS capability was present before
  suspend/resume but not after? [2,3]

I thought Lukasz's latest emails [4,5] indicated that problem 1) still
happened and presumably only happens with Vidya's patch, and 2) also
still happens, but happens even *without* Vidya's patch.  Do I have
that right?

If adding the patch causes 1), obviously we would need to fix that.
It would certainly be good to understand 2) as well, but I guess if
that's a pre-existing problem, ...

Bjorn

[1] https://gist.github.com/semihalf-majczak-lukasz/fb36dfa2eff22911109dfb91ab0fc0e3#file-dmesg-L1762
[2] https://gist.github.com/semihalf-majczak-lukasz/fb36dfa2eff22911109dfb91ab0fc0e3#file-lspci-before-suspend-log-L136
[3] https://gist.github.com/semihalf-majczak-lukasz/fb36dfa2eff22911109dfb91ab0fc0e3#file-lspci-after-suspend-log-L136
[4] https://lore.kernel.org/r/CAFJ_xbr5NjoV1jC3P93N4UgooUuNdCRnrX7HuK=xLtPM5y7EjA@mail.gmail.com
[5] https://lore.kernel.org/r/CAFJ_xboyQyEaDeQ+pZH_YqN52-ALGNqzmmzeyNt6X_Cz-c1w9Q@mail.gmail.com