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Date:   Mon, 7 Oct 2019 08:24:14 -0500
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Dexuan Cui <decui@microsoft.com>
Cc:     "lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        Michael Kelley <mikelley@microsoft.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "driverdev-devel@linuxdriverproject.org" 
        <driverdev-devel@linuxdriverproject.org>,
        Sasha Levin <Alexander.Levin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        "olaf@aepfle.de" <olaf@aepfle.de>,
        "apw@canonical.com" <apw@canonical.com>,
        "jasowang@redhat.com" <jasowang@redhat.com>,
        vkuznets <vkuznets@redhat.com>,
        "marcelo.cerri@canonical.com" <marcelo.cerri@canonical.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        "jackm@mellanox.com" <jackm@mellanox.com>
Subject: Re: [PATCH v2] PCI: PM: Move to D0 before calling
 pci_legacy_resume_early()
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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.
> 
> 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>

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?

> ---
> 
> 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)
> -- 
> 2.19.1
>