Subject: Re: [PATCH v7 2/5] PCI/DPC: Run recovery on device that detected the error

From: Jonathan Cameron <[email-masked]>
Date: Wed, 28 Jan 2026 15:02:43 +0000

On Wed, 28 Jan 2026 20:27:31 +0800
Shuai Xue <[email-masked]> wrote:

> On 1/27/26 6:24 PM, Jonathan Cameron wrote:
> > On Sat, 24 Jan 2026 15:45:54 +0800
> > Shuai Xue <[email-masked]> wrote:
> >   
> >> The current implementation of pcie_do_recovery() assumes that the
> >> recovery process is executed for the device that detected the error.
> >> However, the DPC driver currently passes the error port that experienced
> >> the DPC event to pcie_do_recovery().
> >>
> >> Use the SOURCE ID register to correctly identify the device that
> >> detected the error. When passing the error device, the
> >> pcie_do_recovery() will find the upstream bridge and walk bridges
> >> potentially AER affected. And subsequent commits will be able to
> >> accurately access AER status of the error device.
> >>
> >> Should not observe any functional changes.
> >>
> >> Reviewed-by: Kuppuswamy Sathyanarayanan <[email-masked]>
> >> Signed-off-by: Shuai Xue <[email-masked]>
Hi Shuai,

> >> ---
> >>   drivers/pci/pci.h      |  2 +-
> >>   drivers/pci/pcie/dpc.c | 25 +++++++++++++++++++++----
> >>   drivers/pci/pcie/edr.c |  7 ++++---
> >>   3 files changed, 26 insertions(+), 8 deletions(-)
> >>
...

> >> -void dpc_process_error(struct pci_dev *pdev)
> >> +/**
> >> + * dpc_process_error - handle the DPC error status
> >> + * @pdev: the port that experienced the containment event
> >> + *
> >> + * Return: the device that detected the error.
> >> + *
> >> + * NOTE: The device reference count is increased, the caller must decrement
> >> + * the reference count by calling pci_dev_put().
> >> + */
> >> +struct pci_dev *dpc_process_error(struct pci_dev *pdev)  
> > 
> > Maybe it makes sense to carry the err_port naming for the pci_dev
> > in here as well?  Seems stronger than just relying on people
> > reading the documentation you've added.  
> 
> Good point. I think renaming the parameter would improve clarity. However,
> I'd prefer to handle it in a separate patch to keep this change focused on
> the functional modification. Would that work for you?
> 
Sure. Ideal would be a precursor patch, but if it's much easier to
do on top of this I'm fine with that.

You are absolutely correct that it should be a separate patch!

> >     
> >>   {
> >>   	u16 cap = pdev->dpc_cap, status, source, reason, ext_reason;
> >>   	struct aer_err_info info = {};
> >> +	struct pci_dev *err_dev;
> >>   
> >>   	pci_read_config_word(pdev, cap + PCI_EXP_DPC_STATUS, &status);
> >>   
> >> @@ -279,6 +289,7 @@ void dpc_process_error(struct pci_dev *pdev)
> >>   			pci_aer_clear_nonfatal_status(pdev);
> >>   			pci_aer_clear_fatal_status(pdev);
> >>   		}
> >> +		err_dev = pci_dev_get(pdev);
> >>   		break;
> >>   	case PCI_EXP_DPC_STATUS_TRIGGER_RSN_NFE:
> >>   	case PCI_EXP_DPC_STATUS_TRIGGER_RSN_FE:
> >> @@ -290,6 +301,8 @@ void dpc_process_error(struct pci_dev *pdev)
> >>   				"ERR_FATAL" : "ERR_NONFATAL",
> >>   			 pci_domain_nr(pdev->bus), PCI_BUS_NUM(source),
> >>   			 PCI_SLOT(source), PCI_FUNC(source));
> >> +		err_dev = pci_get_domain_bus_and_slot(pci_domain_nr(pdev->bus),
> >> +					    PCI_BUS_NUM(source), source & 0xff);  
> > 
> > Bunch of replication in her with the pci_warn(). Maybe some local variables?
> > Maybe even rebuild the final parameter from PCI_DEVFN(slot, func) just to make the
> > association with the print really obvious?  
> 
> Agreed. Here's the improved version:
> 
> --- a/drivers/pci/pcie/dpc.c
> +++ b/drivers/pci/pcie/dpc.c
> @@ -293,17 +293,28 @@ struct pci_dev *dpc_process_error(struct pci_dev *pdev)
>                  break;
>          case PCI_EXP_DPC_STATUS_TRIGGER_RSN_NFE:
>          case PCI_EXP_DPC_STATUS_TRIGGER_RSN_FE:
> -               pci_read_config_word(pdev, cap + PCI_EXP_DPC_SOURCE_ID,
> -                                    &source);
> +       {
> +               int domain, bus;
> +               u8 slot, func, devfn;
> +               const char *err_type;
> +
> +               pci_read_config_word(pdev, cap + PCI_EXP_DPC_SOURCE_ID, &source);
> +
> +               /* Extract source device location */
> +               domain = pci_domain_nr(pdev->bus);
> +               bus = PCI_BUS_NUM(source);
> +               slot = PCI_SLOT(source);
> +               func = PCI_FUNC(source);
> +               devfn = PCI_DEVFN(slot, func);
> +
> +               err_type = (reason == PCI_EXP_DPC_STATUS_TRIGGER_RSN_FE) ?
> +                          "ERR_FATAL" : "ERR_NONFATAL";
> +
>                  pci_warn(pdev, "containment event, status:%#06x, %s received from %04x:%02x:%02x.%d\n",
> -                        status,
> -                        (reason == PCI_EXP_DPC_STATUS_TRIGGER_RSN_FE) ?
> -                               "ERR_FATAL" : "ERR_NONFATAL",
> -                        pci_domain_nr(pdev->bus), PCI_BUS_NUM(source),
> -                        PCI_SLOT(source), PCI_FUNC(source));
> -               err_dev = pci_get_domain_bus_and_slot(pci_domain_nr(pdev->bus),
> -                                           PCI_BUS_NUM(source), source & 0xff);
> +                        status, err_type, domain, bus, slot, func);
> +               err_dev = pci_get_domain_bus_and_slot(domain, bus, devfn);
Maybe don't bother with local variables for the things only used once.
e.g.

		err_dev = pci_get_domain_bus_and_slot(domain, bus, PCI_DEVFN(slot, func));

and possibly the same for err_type.

I don't mind though if you prefer to use locals for everything.

>                  break;
> +       }
>          case PCI_EXP_DPC_STATUS_TRIGGER_RSN_IN_EXT:
>                  ext_reason = status & PCI_EXP_DPC_STATUS_TRIGGER_RSN_EXT;
>                  pci_warn(pdev, "containment event, status:%#06x: %s detected\n",
> 
> > 
> > Is there any chance that this might return NULL?   Feels like maybe that's
> > only a possibility on a broken setup, but I'm not sure of all the wonderful
> > races around hotplug and DPC occurring before the OS has caught up.  
> 
> Surprise Down events are handled separately in
> dpc_handle_surprise_removal() and won't reach dpc_process_error().
> Please correct me if I missed anything.

Probably fine. I just didn't check particularly closely.  

Jonathan
> 
> Thanks for valuable comments.
> 
> Best Regards,
> Shuai