Re: [PATCH v3 1/1] PCI/ERR: Fix reset logic in pcie_do_recovery() call

Ethan Zhao
2020-09-28T08:41:14Z

Sathyanarayanan,

On Mon, Sep 28, 2020 at 10:44 AM Kuppuswamy, Sathyanarayanan
<sathyanarayanan.kuppuswamy@linux.intel.com> wrote:
>
> Hi,
>
> On 9/25/20 11:30 AM, Sinan Kaya wrote:
> > On 9/25/2020 2:16 PM, Kuppuswamy, Sathyanarayanan wrote:
> >>>
> >>> If this is a too involved change, DPC driver should restore state
> >>> when hotplug is not supported.
> >> Yes. we can add a condition for hotplug capability check.
> >>>
> >>> DPC driver should be self-sufficient by itself.
> >>>
> >
> > Sounds good.
> >
> >>>> Also for non-fatal errors, if reset is requested then we still need
> >>>> some kind of bus reset call here
> >>>
> >>> DPC should handle both fatal and non-fatal cases
> >> Currently DPC is only triggered for FATAL errors.
> >> and cause a bus reset
> >
> > Thanks for the heads up.
> > This seems to have changed since I looked at the DPC code.
> >
> >>> in hardware already before triggering an interrupt.
> >> Error recovery is not triggered only DPC driver. AER also uses the
> >> same error recovery code. If DPC is not supported, then we still need
> >> reset logic.
> >
> > It sounds like we are cross-talking two issues.
> >
> > 1. no state restore on DPC after FATAL error.
> > Let's fix this.
> Agree. Few more detail about the above issue is,
>
> There are two cases under FATAL error.
>
> FATAL + hotplug - In this case, link will be reseted. And hotplug handler
> will remove the driver state. This case works well with current code.
>
> FATAL + no-hotplug - In this case, link will still be reseted. But
> currently driver state is not properly restored. So I attempted
> to restore it using pci_reset_bus().

Seems you should fix something at device driver side, not do double-reset in
DPC driver, one reset is done by hardware, and you want to do another by
DPC driver ?

Why hardware initiated reset is not enough for you ?

Thanks,
Ethan

> status = reset_link(dev);
> - if (status != PCI_ERS_RESULT_RECOVERED) {
> + if (status == PCI_ERS_RESULT_RECOVERED) {
> + status = PCI_ERS_RESULT_NEED_RESET;
>
> ...
>
> if (status == PCI_ERS_RESULT_NEED_RESET) {
> /*
> - * TODO: Should call platform-specific
> - * functions to reset slot before calling
> - * drivers' slot_reset callbacks?
> + * TODO: Optimize the call to pci_reset_bus()
> + *
> + * There are two components to pci_reset_bus().
> + *
> + * 1. Do platform specific slot/bus reset.
> + * 2. Save/Restore all devices in the bus.
> + *
> + * For hotplug capable devices and fatal errors,
> + * device is already in reset state due to link
> + * reset. So repeating platform specific slot/bus
> + * reset via pci_reset_bus() call is redundant. So
> + * can optimize this logic and conditionally call
> + * pci_reset_bus().
> */
> + pci_reset_bus(dev);
>
> >
> > 2. no bus reset on NON_FATAL error through AER driver path.
> > This already tells me that you need to split your change into
> > multiple patches.
> >
> > Let's talk about this too. bus reset should be triggered via
> > AER driver before informing the recovery.
> But as per error recovery documentation, any call to
> ->error_detected() or ->mmio_enabled() can request
> PCI_ERS_RESULT_NEED_RESET. So we need to add code
> to do the actual reset before calling ->slot_reset()
> callback. So call to pci_reset_bus() fixes this
> issue.
>
> if (status == PCI_ERS_RESULT_NEED_RESET) {
> + pci_reset_bus(dev);
>
>
> >
> > if (status == PCI_ERS_RESULT_NEED_RESET) {
> > /*
> > * TODO: Should call platform-specific
> > * functions to reset slot before calling
> > * drivers' slot_reset callbacks?
> > */
> > status = PCI_ERS_RESULT_RECOVERED;
> > pci_dbg(dev, "broadcast slot_reset message\n");
> > pci_walk_bus(bus, report_slot_reset, &status);
> > }
> >
>
> --
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer