Re: [PATCH v7 3/9] PCI: Avoid saving config space state if inaccessible

[Niklas Schnelle <schnelle@linux.ibm.com>]

On Wed, 2026-01-07 at 10:32 -0800, Farhan Ali wrote:
> The current reset process saves the device's config space state before reset
> and restores it afterward. However errors may occur unexpectedly and it may
> then be impossible to save config space because the device may be inaccessible
> (e.g. DPC) or config space may be corrupted. This results in saving corrupted
> values that get written back to the device during state restoration.
> 
> With a reset we want to recover/restore the device into a functional
> state. So avoid saving the state of the config space when the device config
> space is inaccessible.
> 
> Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
> ---
>  drivers/pci/pci.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index c105e285cff8..74d21c97654d 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -4960,6 +4960,7 @@ EXPORT_SYMBOL_GPL(pci_dev_unlock);
>  
>  static void pci_dev_save_and_disable(struct pci_dev *dev)
>  {
> +	u32 val;
>  	const struct pci_error_handlers *err_handler =
>  			dev->driver ? dev->driver->err_handler : NULL;
>  
> @@ -4980,6 +4981,12 @@ static void pci_dev_save_and_disable(struct pci_dev *dev)
>  	 */
>  	pci_set_power_state(dev, PCI_D0);
>  
> +	pci_read_config_dword(dev, PCI_COMMAND, &val);

Since the PCI_COMMAND field is only 16 bits I think it warrants a
comment that you're reading both PCI_COMMAND and PCI_STATUS and that
both together should never be 0xffffffff and why. I think at least
PCI_STATUS_PARITY should never be set in a config space we want to
restore.

> +	if (PCI_POSSIBLE_ERROR(val)) {
> +		pci_warn(dev, "Device config space inaccessible\n");
> +		return;
> +	}
> +
>  	pci_save_state(dev);
>  	/*
>  	 * Disable the device by clearing the Command register, except for

Functionally this looks good to me and I agree that with both DPC and
s390x PCI error state behavior this makes sense.

Thanks,
Niklas