Re: [PATCH] PCI: vmd: Allow VMD PM to use PCI core PM code

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Vaibhav, Rafael for suspend/resume question]

On Fri, Jul 31, 2020 at 01:15:44PM -0400, Jon Derrick wrote:
> The pci_save_state call in vmd_suspend can be performed by
> pci_pm_suspend_irq. This allows the call to pci_prepare_to_sleep into
> ASPM flow.

Add "()" after function names so they don't look like English words.

What is this "ASPM flow"?  The only ASPM-related code should be
configuration (enable/disable ASPM) (which happens at
enumeration-time, not suspend/resume time) and save/restore if we turn
the device off and we have to reconfigure it when we turn it on again.

> The pci_restore_state call in vmd_resume was restoring state after
> pci_pm_resume->pci_restore_standard_config had already restored state.
> It's also been suspected that the config state should be restored before
> re-requesting IRQs.
> 
> Remove the pci_{save,restore}_state calls in vmd_{suspend,resume} in
> order to allow proper flow through PCI core power management ASPM code.
> 
> Cc: Kai-Heng Feng <kai.heng.feng@canonical.com>
> Cc: You-Sheng Yang <vicamo.yang@canonical.com>
> Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
> ---
>  drivers/pci/controller/vmd.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
> index 76d8acbee7d5..15c1d85d8780 100644
> --- a/drivers/pci/controller/vmd.c
> +++ b/drivers/pci/controller/vmd.c
> @@ -719,7 +719,6 @@ static int vmd_suspend(struct device *dev)
>  	for (i = 0; i < vmd->msix_count; i++)
>  		devm_free_irq(dev, pci_irq_vector(pdev, i), &vmd->irqs[i]);
>  
> -	pci_save_state(pdev);

The VMD driver uses generic PM, not legacy PCI PM, so I think removing
the save/restore state from your suspend/resume functions is the right
thing to do.  You should only need to do VMD-specific things there.

I'm not even sure you need to free/request the IRQs in your
suspend/resume.  Maybe Rafael or Vaibhav know.

I just think the justification in the commit log is wrong.

>  	return 0;
>  }
>  
> @@ -737,7 +736,6 @@ static int vmd_resume(struct device *dev)
>  			return err;
>  	}
>  
> -	pci_restore_state(pdev);
>  	return 0;
>  }
>  #endif
> -- 
> 2.18.1
>