Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for non-hotplug capable devices

[Kuppuswamy, Sathyanarayanan]

Hi,

On 5/26/20 8:00 PM, Oliver O'Halloran wrote:
> On Wed, May 27, 2020 at 12:00 PM Kuppuswamy, Sathyanarayanan
> <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx> wrote:
> > Hi,
> >
> > On 5/21/20 7:56 PM, Yicong Yang wrote:
> > > On 2020/5/22 3:31, Kuppuswamy, Sathyanarayanan wrote:
> > > >
> > > Not exactly. In pci_bus_error_reset(), we call pci_slot_reset() only if it's
> > > hotpluggable. But we always call pci_bus_reset() to perform a secondary bus
> > > reset for the bridge. That's what I think is unnecessary for a normal link,
> > > and that's what reset link indicates us to do. The slot reset is introduced
> > > in the process only to solve side effects. (c4eed62a2143, PCI/ERR: Use slot reset if available)
> >
> > IIUC, pci_bus_reset() will do slot reset if its supported (hot-plug
> > capable slots). If its not supported then it will attempt secondary
> > bus reset. So secondary bus reset will be attempted only if slot
> > reset is not supported.
> >
> > Since reported_error_detected() requests us to do reset, we will have
> > to attempt some kind of reset before we call ->slot_reset() right?
>
> Yes, the driver returns PCI_ERS_RESULT_NEED_RESET from
> ->error_detected() to indicate that it doesn't know how to recover
> from the error. How that reset is performed doesn't really matter, but
> it does need to happen.
>
>
> > > PCI_ERS_RESULT_NEED_RESET indicates that the driver
> > > wants a platform-dependent slot reset and its ->slot_reset() method to be called then.
> > > I don't think it's same as slot reset mentioned above, which is only for hotpluggable
> > > ones.
> > What you think is the correct reset implementation ? Is it something
> > like this?
> >
> > if (hotplug capable)
> >      try_slot_reset()
> > else
> >      do_nothing()
>
> Looks broken to me, but all the reset handling is a rat's nest so
> maybe I'm missing something. In the case of a DPC trip the link is
> disabled which has the side-effect of hot-resetting the downstream
> device. Maybe it's fine?
Yes, in case of DPC (Fatal errors) link is already reset. So we
don't need any special handling. This reset logic is mainly for
non-fatal errors.
> As an aside, why do we have both ->slot_reset() and ->reset_done() in
> the error handling callbacks? Seems like their roles are almost
> identical.
Not sure.I think reset_done() is final cleanup.
> Oliver