Messages in this thread | | | Subject | Re: [PATCH v2] PCI: PM: Move to D0 before calling pci_legacy_resume_early() | From | "Rafael J. Wysocki" <> | Date | Thu, 10 Oct 2019 18:45:02 +0200 |
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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@kernel.org> >>>> Sent: Monday, October 7, 2019 6:24 AM >>>> To: Dexuan Cui <decui@microsoft.com> >>>> Cc: lorenzo.pieralisi@arm.com; linux-pci@vger.kernel.org; Michael Kelley >>>> <mikelley@microsoft.com>; linux-hyperv@vger.kernel.org; >>>> linux-kernel@vger.kernel.org; driverdev-devel@linuxdriverproject.org; Sasha >>>> Levin <Alexander.Levin@microsoft.com>; Haiyang Zhang >>>> <haiyangz@microsoft.com>; KY Srinivasan <kys@microsoft.com>; >>>> olaf@aepfle.de; apw@canonical.com; jasowang@redhat.com; vkuznets >>>> <vkuznets@redhat.com>; marcelo.cerri@canonical.com; Stephen Hemminger >>>> <sthemmin@microsoft.com>; jackm@mellanox.com >>>> 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@microsoft.com> >>>> 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.
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