Re: [PATCH v3] PCI/PM: Restore BARs after powering up during enumeration

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Oct 15, 2026 at 10:08:11AM +0800, Keng-Yu Lin wrote:
> Commit 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when
> initializing") added pci_pm_power_up_and_verify_state() to pci_pm_init().
> The helper ignores pci_power_up()'s return value indicating that BARs
> need restoring. Its resume callers restore saved configuration
> afterwards; pci_pm_init() does not.
> 
> D3hot-to-D0 may reset a device and lose its BARs (PCI PM 1.2, sec 5.4.1).
> After enumeration powers it up, pci_enable_device() reads D0 and skips
> the full power-up path. Previously, a device still in D3hot at enable
> time took that path, including BAR restoration.
> 
> On AMD Venice SP7, two AMD xHCI controllers [1022:17d2] are in runtime
> D3hot with No_Soft_Reset clear before kdump. Diagnostic reads on
> v7.3-rc6-37 show the following for 0000:01:00.4 in the crash kernel:
> 
>                                    PMCSR      BAR0
>   before the platform power call   0003       f4100004
>   after the platform power call    0003       f4100004
>   after native D0 power-up         0000       00000004
> 
> The upper BAR DWORD stays zero. pci_power_up() returns 1, but the BAR
> address remains zero while dev->resource[0] still contains 0xf4100000.
> Without BAR restoration, the crash kernel hangs during boot. The
> last console output includes:
> 
>   pci 0000:01:00.4: enabling device (0000 -> 0002)
> 
> Restoring both controllers' BARs gives matching readbacks and allows
> kdump to save a vmcore and reboot. An AMD Turin xHCI [1022:1557] shows
> the same BAR loss; restoring its BAR also allows kdump to complete.
> 
> Read the initial power state first. Otherwise, pci_power_up() may
> request a BAR restore based on a cached PCI_UNKNOWN state, even
> when the device is already in D0.
> 
> For devices already in D0, only synchronize the platform state so
> that ACPI calls such as _REG still run. For other states, use
> pci_set_full_power_state() to power up the device and restore BARs
> when needed.
> 
> Suggested-by: Mario Limonciello <mario.limonciello@amd.com>
> Suggested-by: Rafael J. Wysocki <rafael@kernel.org>
> Fixes: 4d4c10f763d7 ("PCI: Explicitly put devices into D0 when initializing")
> Link: https://lore.kernel.org/r/CAJZ5v0ie2AvCbdv8-zkpYzHLcTwUPUj+=WWOQjDAPmSepSAQPg@mail.gmail.com/
> Cc: stable@vger.kernel.org
> Signed-off-by: Keng-Yu Lin <keng-yu.lin@hpe.com>

Applied to pci/pm for v7.4, thanks!

> ---
> 
> Changes in v3:
> - Use Rafael's sequence: sync only the platform state for devices
>   already in D0, and use pci_set_full_power_state() otherwise.
> - The D0 path no longer runs the full helper's ASPM update.
> 
> Tested with diagnostic prints on AMD Venice SP7 and Turin. Normal
> boots made no BAR writes from this path. The crash kernels restored
> only the cleared xHCI BARs (two on Venice, one on Turin), with matching
> readbacks. Both systems saved a vmcore and rebooted.
> 
> v2: https://lore.kernel.org/r/20261012104645.975190-1-keng-yu.lin@hpe.com/
> 
>  drivers/pci/pci.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 8cc6a89130b5..895969fe4520 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3255,7 +3255,15 @@ void pci_pm_init(struct pci_dev *dev)
>  	}
>  
>  poweron:
> -	pci_pm_power_up_and_verify_state(dev);
> +	pci_update_current_state(dev, PCI_UNKNOWN);
> +	if (dev->current_state == PCI_D0) {
> +		/* No need to do a full power-up, just sync-up the platform state. */
> +		platform_pci_set_power_state(dev, PCI_D0);
> +	} else {
> +		/* Power up the device and restore BARs if necessary. */
> +		pci_set_full_power_state(dev, false);
> +	}
> +	pci_update_current_state(dev, PCI_D0);
>  	pm_runtime_forbid(&dev->dev);
>  
>  	/*
> 
> base-commit: 7b63ef2d55f24519e7e9e5f4d15dbea03f126e40
> -- 
> 2.43.0