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SubjectRe: [PATCH v12 05/15] PCI/ERR: Simplify by using pci_upstream_bridge()
On Thu, Dec 03, 2020 at 06:45:00PM +0000, Kelley, Sean V wrote:
> Just confirming that when switched from dev->bus->self to
> pci_upstream_bridge() we’re okay with the NULL case:
>
> > On Nov 20, 2020, at 4:10 PM, Sean V Kelley <sean.v.kelley@intel.com> wrote:
> >
> > Use pci_upstream_bridge() in place of dev->bus->self. No functional change
> > intended.
> >
> > [bhelgaas: split to separate patch]
> > Link: https://lore.kernel.org/r/20201002184735.1229220-6-seanvk.dev@oregontracks.org
> > Signed-off-by: Sean V Kelley <sean.v.kelley@intel.com>
> > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> > Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> > ---
> > drivers/pci/pcie/err.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> > index db149c6ce4fb..05f61da5ed9d 100644
> > --- a/drivers/pci/pcie/err.c
> > +++ b/drivers/pci/pcie/err.c
> > @@ -159,7 +159,7 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> > */
> > if (!(pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
> > pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM))
> > - dev = dev->bus->self;
> > + dev = pci_upstream_bridge(dev);
>
> The only case where pci_upstream_bridge(dev) could be NULL is if
> dev->bus is the root bus and we are being selective based on the
> type.

Yes, pci_upstream_bridge(dev) returns NULL if dev is on a root bus.
I think bus->self is NULL for root buses anyway, so I think this patch
is OK at least at this point in the series.

> Even later in this series when we actually add in RC_EC/RC_END we
> maintain the conditional checks:
>
> https://lore.kernel.org/linux-pci/20201121001036.8560-11-sean.v.kelley@intel.com/
>
> pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>
> @@ -174,10 +180,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>
>
> /*
> * Error recovery runs on all subordinates of the bridge. If the
> - * bridge detected the error, it is cleared at the end.
> + * bridge detected the error, it is cleared at the end. For RCiEPs
> + * we should reset just the RCiEP itself.
>
> */
> if (type == PCI_EXP_TYPE_ROOT_PORT ||
> - type == PCI_EXP_TYPE_DOWNSTREAM)
> + type == PCI_EXP_TYPE_DOWNSTREAM ||
> + type == PCI_EXP_TYPE_RC_EC ||
> + type == PCI_EXP_TYPE_RC_END)
> bridge = dev;
> else
> bridge = pci_upstream_bridge(dev);
>
> I believe we are okay here.

Well, I think we're at least no worse than today. Today we keep
"bridge == dev" for Root Ports and Downstream Ports, and use
"bridge = dev->bus->self" for everything else.

After this series we keep "bridge == dev" for RCEC and RCiEPs in
addition.

I'm not sure about PCI_EXP_TYPE_PCI_BRIDGE, which is a PCIe-to-PCI
bridge. According to the ancient "PCI Express to PCI/PCI-X Bridge
Specification" r1.0 of July 14, 2003, sec 5.23, these bridges can have
an AER Capability (with different format that I don't see mentioned
elsewhere).

But this AER Capability doesn't have the Root registers, so I assume
it would have to be below a Root Port in order to actually signal the
errors, which would mean it could not be on a root bus.

So I don't really *love* the fact that we use pci_upstream_bridge()
and rely on these assumptions that the result will not be NULL, but I
guess it's OK for now.

> > bus = dev->subordinate;
> >
> > pci_dbg(dev, "broadcast error_detected message\n");
> > --
> > 2.29.2
> >
> >
>

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