linux-kernel - Re: [PATCH v3 1/1] PCI/ERR: Fix reset logic in pcie_do

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Date:   Mon, 28 Sep 2020 16:41:00 +0800
From:   Ethan Zhao <xerces.zhao@...il.com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Sinan Kaya <okaya@...nel.org>, Bjorn Helgaas <helgaas@...nel.org>,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, ashok.raj@...el.com,
        Jay Vosburgh <jay.vosburgh@...onical.com>
Subject: Re: [PATCH v3 1/1] PCI/ERR: Fix reset logic in pcie_do_recovery() call

Sathyanarayanan,

On Mon, Sep 28, 2020 at 10:44 AM Kuppuswamy, Sathyanarayanan
<sathyanarayanan.kuppuswamy@...ux.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