Re: [PATCH v2] PCI: PM: Move to D0 before calling pci_legacy_resume_early()
From: Rafael J. Wysocki
Date: Thu Oct 10 2019 - 12:45:11 EST
On 10/8/2019 9:56 PM, Bjorn Helgaas wrote:
On Tue, Oct 08, 2019 at 07:32:27PM +0200, Rafael J. Wysocki wrote:
On 10/7/2019 8:57 PM, Dexuan Cui wrote:
-----Original Message-----
From: Bjorn Helgaas <helgaas@xxxxxxxxxx>
Sent: Monday, October 7, 2019 6:24 AM
To: Dexuan Cui <decui@xxxxxxxxxxxxx>
Cc: lorenzo.pieralisi@xxxxxxx; linux-pci@xxxxxxxxxxxxxxx; Michael Kelley
<mikelley@xxxxxxxxxxxxx>; linux-hyperv@xxxxxxxxxxxxxxx;
linux-kernel@xxxxxxxxxxxxxxx; driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx; Sasha
Levin <Alexander.Levin@xxxxxxxxxxxxx>; Haiyang Zhang
<haiyangz@xxxxxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>;
olaf@xxxxxxxxx; apw@xxxxxxxxxxxxx; jasowang@xxxxxxxxxx; vkuznets
<vkuznets@xxxxxxxxxx>; marcelo.cerri@xxxxxxxxxxxxx; Stephen Hemminger
<sthemmin@xxxxxxxxxxxxx>; jackm@xxxxxxxxxxxx
Subject: Re: [PATCH v2] PCI: PM: Move to D0 before calling
pci_legacy_resume_early()
On Wed, Aug 14, 2019 at 01:06:55AM +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_D0,
but the current code misses the pci_legacy_resume_early() path, so the
state remains in PCI_UNKNOWN in that path. As a result, in the resume
phase of hibernation, this causes an error for the Mellanox VF driver,
which fails to enable MSI-X because pci_msi_supported() is false due
to dev->current_state != PCI_D0:
mlx4_core a6d1:00:02.0: Detected virtual function - running in slave mode
mlx4_core a6d1:00:02.0: Sending reset
mlx4_core a6d1:00:02.0: Sending vhcr0
mlx4_core a6d1:00:02.0: HCA minimum page size:512
mlx4_core a6d1:00:02.0: Timestamping is not supported in slave mode
mlx4_core a6d1:00:02.0: INTx is not supported in multi-function mode,
aborting
PM: dpm_run_callback(): pci_pm_thaw+0x0/0xd7 returns -95
PM: Device a6d1:00:02.0 failed to thaw: error -95
To be more accurate, the "resume" phase means the "thaw" callbacks which
run before the system enters hibernation: when the user runs the command
"echo disk > /sys/power/state" for hibernation, first the kernel "freezes"
all the devices and creates a hibernation image, then the kernel "thaws"
the devices including the disk/NIC, writes the memory to the disk, and
powers down. This patch fixes the error message for the Mellanox VF driver
in this phase.
Wordsmithing nit: what the patch does is not "fix the error message";
what it does is fix the *problem*, i.e., the fact that we can't
operate the device because we can't enable MSI-X. The message is only
a symptom.
IIUC the relevant part of the system hibernation sequence is:
pci_pm_freeze_noirq
pci_pm_thaw_noirq
pci_pm_thaw
And the execution flow is:
pci_pm_freeze_noirq
if (pci_has_legacy_pm_support(pci_dev)) # true for mlx4
pci_legacy_suspend_late(dev, PMSG_FREEZE)
pci_pm_set_unknown_state
dev->current_state = PCI_UNKNOWN # <---
pci_pm_thaw_noirq
if (pci_has_legacy_pm_support(pci_dev)) # true
pci_legacy_resume_early(dev) # noop; mlx4 doesn't implement
pci_pm_thaw # returns -95 EOPNOTSUPP
if (pci_has_legacy_pm_support(pci_dev)) # true
pci_legacy_resume
drv->resume
mlx4_resume # mlx4_driver.resume (legacy)
mlx4_load_one
mlx4_enable_msi_x
pci_enable_msix_range
__pci_enable_msix_range
__pci_enable_msix
if (!pci_msi_supported())
if (dev->current_state != PCI_D0) # <---
return 0
return -EINVAL
err = -EOPNOTSUPP
"INTx is not supported ..."
(These are just my notes; you don't need to put them all into the
commit message. I'm just sharing them in case I'm not understanding
correctly.)
When the system starts again, a fresh kernel starts to run, and when the
kernel detects that a hibernation image was saved, the kernel "quiesces"
the devices, and then "restores" the devices from the saved image. In this
path:
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 broken and doesn't need my patch.
The cc list suggests that this might be a fix for a user-reported
problem. Is there a launchpad or similar link you could include here?
Should this be marked for stable?
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
This looks like a bugfix for 5839ee7389e8 ("PCI / PM: Force devices to
D0 in pci_pm_thaw_noirq()") so maybe it should be marked for stable as
5839ee7389e8 was?
Rafael, could you confirm?
No, it is not a bug fix for that commit. The underlying issue would be
there without that commit too.
Oh, right, I dunno what I was thinking, sorry.
--- a/drivers/pci/pci-driver.c
+++ b/drivers/pci/pci-driver.c
@@ -1074,15 +1074,16 @@ static int pci_pm_thaw_noirq(struct device
*dev)
return error;
}
- if (pci_has_legacy_pm_support(pci_dev))
- return pci_legacy_resume_early(dev);
-
/*
* pci_restore_state() requires the device to be in D0 (because of MSI
* restoration among other things), so force it into D0 in case the
* driver's "freeze" callbacks put it into a low-power state directly.
*/
pci_set_power_state(pci_dev, PCI_D0);
+
+ if (pci_has_legacy_pm_support(pci_dev))
+ return pci_legacy_resume_early(dev);
+
pci_restore_state(pci_dev);
if (drv && drv->pm && drv->pm->thaw_noirq)
--
2.19.1
The patch looks reasonable to me, but the comment above the
pci_set_power_state() call needs to be updated too IMO.
Hmm.
1) pci_restore_state() mainly writes config space, which doesn't
require the device to be in D0. The only thing I see that would
require D0 is the MSI-X MMIO space, so to be more specific, the
comment could say "restoring the MSI-X *MMIO* state requires the
device to be in D0".
But I think you meant some other comment change. Did you mean
something along the lines of "a legacy drv->resume_early() callback
and pci_restore_state() both require the device to be in D0"?
Yes, I did.