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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Mon, 13 Jan 2020 11:01:28 +0100
Message-ID: <CAJZ5v0jgdfAG_BDefdSQFV9hM61o68Aj31PxShNxxcpsYFpxgw@mail.gmail.com>
Subject: Re: [PATCH] PCI/PM: Print the pci config space of devices before suspend
To:     Chen Yu <yu.c.chen@intel.com>
Cc:     Linux PCI <linux-pci@vger.kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <lenb@kernel.org>,
        Linux PM <linux-pm@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Jan 13, 2020 at 7:08 AM Chen Yu <yu.c.chen@intel.com> wrote:
>
> The pci config space was found to be insane during resume

I wouldn't call it "insane".

It probably means that the device was not present or not accessible
during hibernation and now it appears to be present (maybe the restore
kernel found it and configured it).

> from hibernation(S4, or suspend to disk) on a VM:
>
>  serial 0000:00:16.3: restoring config space at offset 0x14
>  (was 0x9104e000, writing 0xffffffff)
>
> Either the snapshot on the disk has been scribbled or the pci
> config space becomes invalid before suspend.

Or, most likely, the above.

> To narrow down and benefit future debugging, print the pci config space
> being saved before suspend, which is symmetric to the log
> in pci_restore_config_dword().

But the code change makes sense to me.

> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
> Cc: Len Brown <lenb@kernel.org>
> Cc: linux-pci@vger.kernel.org
> Cc: linux-pm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> ---
>  drivers/pci/pci.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index e87196cc1a7f..34cde70440c3 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1372,8 +1372,11 @@ int pci_save_state(struct pci_dev *dev)
>  {
>         int i;
>         /* XXX: 100% dword access ok here? */
> -       for (i = 0; i < 16; i++)
> +       for (i = 0; i < 16; i++) {
>                 pci_read_config_dword(dev, i * 4, &dev->saved_config_space[i]);
> +               pci_dbg(dev, "saving config space at offset %#x (reading %#x)\n",
> +                       i * 4, dev->saved_config_space[i]);
> +       }
>         dev->state_saved = true;
>
>         i = pci_save_pcie_state(dev);
> --
> 2.17.1
>