Re: [RFC PATCH 5/9] PCI/AER: Apply function level reset to RCiEP on fatal error

[Sean V Kelley]

On 28 Jul 2020, at 6:27, Zhuo, Qiuxu wrote:

> > From: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> > Sent: Monday, July 27, 2020 7:17 PM
> > To: Kelley, Sean V <sean.v.kelley@xxxxxxxxx>
> > Cc: bhelgaas@xxxxxxxxxx; rjw@xxxxxxxxxxxxx; ashok.raj@xxxxxxxxxx; 
> > Luck,
> > Tony <tony.luck@xxxxxxxxx>;
> > sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx; 
> > linux-pci@xxxxxxxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx; Zhuo, Qiuxu <qiuxu.zhuo@xxxxxxxxx>
> > Subject: Re: [RFC PATCH 5/9] PCI/AER: Apply function level reset to 
> > RCiEP
> > on fatal error
> >
> > On Fri, 24 Jul 2020 10:22:19 -0700
> > Sean V Kelley <sean.v.kelley@xxxxxxxxx> wrote:
> >
> > > From: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>
> > >
> > > Attempt to do function level reset for an RCiEP associated with an
> > > RCEC device on fatal error.
> >
> > I'd like to understand more on your reasoning for flr here.
> > Is it simply that it is all we can do, or is there some basis in a 
> > spec
> > somewhere?
>
> Yes. Though there isn't the link reset for the RCiEP here, I think we 
> should still be able to reset the RCiEP via FLR on fatal error, if the 
> RCiEP supports FLR.
>
> -Qiuxu

Also see PCIe 5.0-1, Sec. 6.6.2 Function Level Reset (FLR)

Implementation of FLR is optional (not required), but is strongly 
recommended. For an example use case consider CXL. Function 0 DVSEC 
instances control for the CXL functionality of the entire CXL device. 
FLR may succeed in recovering from CXL.io domain errors.

Thanks,

Sean

> > > Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@xxxxxxxxx>
> > > ---
> > >  drivers/pci/pcie/err.c | 31 ++++++++++++++++++++++---------
> > >  1 file changed, 22 insertions(+), 9 deletions(-)
> > >
> > > diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c index
> > > 044df004f20b..9b3ec94bdf1d 100644
> > > --- a/drivers/pci/pcie/err.c
> > > +++ b/drivers/pci/pcie/err.c
> > > @@ -170,6 +170,17 @@ static void pci_walk_dev_affected(struct
> > pci_dev *dev, int (*cb)(struct pci_dev
> > >  }
> > >  }
> > >
> > > +static enum pci_channel_state flr_on_rciep(struct pci_dev *dev) {
> > > +if (!pcie_has_flr(dev))
> > > +return PCI_ERS_RESULT_NONE;
> > > +
> > > +if (pcie_flr(dev))
> > > +return PCI_ERS_RESULT_DISCONNECT;
> > > +
> > > +return PCI_ERS_RESULT_RECOVERED;
> > > +}
> > > +
> > >  pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> > >  enum pci_channel_state state,
> > >  pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
> > @@ -191,15
> > > +202,17 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
> > >  if (state == pci_channel_io_frozen) {
> > >  pci_walk_dev_affected(dev, report_frozen_detected,
> > &status);
> > >  if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END) {
> > > -pci_warn(dev, "link reset not possible for RCiEP\n");
> > > -status = PCI_ERS_RESULT_NONE;
> > > -goto failed;
> > > -}
> > > -
> > > -status = reset_link(dev);
> > > -if (status != PCI_ERS_RESULT_RECOVERED) {
> > > -pci_warn(dev, "link reset failed\n");
> > > -goto failed;
> > > +status = flr_on_rciep(dev);
> > > +if (status != PCI_ERS_RESULT_RECOVERED) {
> > > +pci_warn(dev, "function level reset failed\n");
> > > +goto failed;
> > > +}
> > > +} else {
> > > +status = reset_link(dev);
> > > +if (status != PCI_ERS_RESULT_RECOVERED) {
> > > +pci_warn(dev, "link reset failed\n");
> > > +goto failed;
> > > +}
> > >  }
> > >  } else {
> > >  pci_walk_dev_affected(dev, report_normal_detected,
> > &status);