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From:   Dexuan Cui <decui@microsoft.com>
To:     Bjorn Helgaas <helgaas@kernel.org>
CC:     "lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
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        <driverdev-devel@linuxdriverproject.org>,
        Sasha Levin <Alexander.Levin@microsoft.com>,
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        vkuznets <vkuznets@redhat.com>,
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        Stephen Hemminger <sthemmin@microsoft.com>,
        "jackm@mellanox.com" <jackm@mellanox.com>
Subject: RE: [PATCH] PCI: PM: Also move to D0 before calling
 pci_legacy_resume_early()
Thread-Topic: [PATCH] PCI: PM: Also move to D0 before calling
 pci_legacy_resume_early()
Thread-Index: AdVOGUCbZsj/msiiS0u0Knw2VZMQCQABOjuAAABxRyA=
Date:   Thu, 8 Aug 2019 20:02:36 +0000
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> From: Bjorn Helgaas <helgaas@kernel.org>
> Sent: Thursday, August 8, 2019 12:19 PM
> To: Dexuan Cui <decui@microsoft.com>
>=20
> On Thu, Aug 08, 2019 at 06:46:51PM +0000, Dexuan Cui wrote:
> >
> > In pci_legacy_suspend_late(), the device state is moved to PCI_UNKNOWN.
> > In pci_pm_thaw_noirq(), the state is supposed to be moved back to PCI_D=
0,
> > but the current code misses the pci_legacy_resume_early() path, so the
> > state remains in PCI_UNKNOWN in that path, and during hiberantion this
> > causes an error for the Mellanox VF driver, which fails to enable
> > MSI-X: pci_msi_supported() is false due to dev->current_state !=3D PCI_=
D0:
>=20
> s/hiberantion/hibernation/

Thanks for spoting this typo! :-)
=20
> Actually, it sounds more like "during *resume*, this causes an error",
> so maybe you want s/hiberantion/resume/ instead?

Yes, it's during "resume", and to be more accurate, it happens during the
"resume" of the "thaw" phase: when we run "echo disk > /sys/power/state",
first the kernel "freezes" all the devices and create a hibernation image, =
then
the kernel "thaws" the devices including the disk/NIC, and writes the memor=
y
to the disk and powers down. This patch fixes the error message for the
Mellanox VF driver in this phase.=20

When the system starts again, a fresh kernel starts to run, and when the ke=
rnel
detects that a hibernation image was saved, the kernel "quiesces" the devic=
es,
and "restores" the devices from the saved image. Here device_resume_noirq()
-> ... -> pci_pm_restore_noirq() -> pci_pm_default_resume_early() ->
pci_power_up() moves the device states back to PCI_D0. This path is not bro=
ken
and doesn't need my patch.=20

Thanks,
-- Dexuan