# RE: \[PATCH v2\] PCI: PM: Move to D0 before calling pci\_legacy\_resume\_early()

- From: Dexuan Cui \<decui@microsoft.com\>
- Date: 2019-09-03 00:34:47 
- List: linux-hyperv
- Page: https://ratatoskr.run/linux-hyperv/2019/09/5706445
- Thread: https://ratatoskr.run/linux-pci/2019/08/5686811/t.md

```text
> From: Dexuan Cui <decui@microsoft.com>
> Sent: Tuesday, August 13, 2019 6:07 PM
> To: <redacted>; bhelgaas@google.com;
> linux-pci@vger.kernel.org
> Cc: Michael Kelley <redacted>; <redacted>;
> linux-kernel@vger.kernel.org; driverdev-devel@linuxdriverproject.org; Sasha
> Levin [ref]; Haiyang Zhang
> [ref]; KY Srinivasan [ref];
> olaf@aepfle.de; apw@canonical.com; jasowang@redhat.com; vkuznets
> [ref]; marcelo.cerri@canonical.com; Stephen Hemminger
> [ref]; jackm@mellanox.com; Dexuan Cui
> [ref]
> Subject: [PATCH v2] PCI: PM: Move to D0 before calling
> pci_legacy_resume_early()
> 
> 
> 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.
> 
> 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.
> 
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> ---
> 
> changes in v2:
> 	Updated the changelog with more details.
> 
>  drivers/pci/pci-driver.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 36dbe960306b..27dfc68db9e7 100644
> --- 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)
> --

Hi, Lorenzo, Bjorn,

Can you please take a look at the v2 ?

Thanks,
-- Dexuan
```