Re: [PATCH v2] PCI: Set up runtime PM on devices that don't support PCI PM

[Bjorn Helgaas <helgaas@kernel.org>]

On Wed, Jun 11, 2025 at 06:31:16PM -0500, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@amd.com>
> 
> commit 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when
> initializing") intended to put PCI devices into D0, but in doing so
> unintentionally changed runtime PM initialization not to occur on
> devices that don't support PCI PM.  This caused a regression in vfio-pci
> due to an imbalance with it's use.
> 
> Adjust the logic in pci_pm_init() so that even if PCI PM isn't supported
> runtime PM is still initialized.
> 
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Reported-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
> Closes: https://lore.kernel.org/linux-pci/20250424043232.1848107-1-superm1@kernel.org/T/#m7e8929d6421690dc8bd6dc639d86c2b4db27cbc4
> Reported-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
> Closes: https://lore.kernel.org/linux-pci/20250424043232.1848107-1-superm1@kernel.org/T/#m40d277dcdb9be64a1609a82412d1aa906263e201
> Tested-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
> Fixes: 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when initializing")
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>

4d4c10f763d7 appeared in v6.16-rc1, so I applied this to pci/for-linus
for v6.16, thanks for the quick resolution!

> ---
> v2:
>  * remove pointless return
> ---
>  drivers/pci/pci.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 3dd44d1ad829b..160a9a482c732 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3222,14 +3222,14 @@ void pci_pm_init(struct pci_dev *dev)
>  	/* find PCI PM capability in list */
>  	pm = pci_find_capability(dev, PCI_CAP_ID_PM);
>  	if (!pm)
> -		return;
> +		goto poweron;
>  	/* Check device's ability to generate PME# */
>  	pci_read_config_word(dev, pm + PCI_PM_PMC, &pmc);
>  
>  	if ((pmc & PCI_PM_CAP_VER_MASK) > 3) {
>  		pci_err(dev, "unsupported PM cap regs version (%u)\n",
>  			pmc & PCI_PM_CAP_VER_MASK);
> -		return;
> +		goto poweron;
>  	}
>  
>  	dev->pm_cap = pm;
> @@ -3274,6 +3274,7 @@ void pci_pm_init(struct pci_dev *dev)
>  	pci_read_config_word(dev, PCI_STATUS, &status);
>  	if (status & PCI_STATUS_IMM_READY)
>  		dev->imm_ready = 1;
> +poweron:
>  	pci_pm_power_up_and_verify_state(dev);
>  	pm_runtime_forbid(&dev->dev);
>  	pm_runtime_set_active(&dev->dev);
> -- 
> 2.43.0
>