linux-kernel - Re: [PATCH v2] PCI/EDR: Clear PCIe Device Status errors after EDR error recovery

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Message-ID: <20230407224142.GA3829056@bhelgaas>
Date:   Fri, 7 Apr 2023 17:41:42 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     "Natu, Mahesh" <mahesh.natu@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI/EDR: Clear PCIe Device Status errors after EDR
 error recovery

On Fri, Apr 07, 2023 at 03:19:32PM -0700, Sathyanarayanan Kuppuswamy wrote:
> On 4/7/23 9:46 AM, Bjorn Helgaas wrote:
> > On Thu, Apr 06, 2023 at 10:31:20PM -0700, Sathyanarayanan Kuppuswamy wrote:
> >> On 4/6/23 3:21 PM, Bjorn Helgaas wrote:
> >>> On Thu, Apr 06, 2023 at 02:52:02PM -0700, Sathyanarayanan Kuppuswamy wrote:
> >>>> On 4/6/23 2:07 PM, Bjorn Helgaas wrote:
> >>>>> On Wed, Mar 15, 2023 at 04:54:49PM -0700, Kuppuswamy Sathyanarayanan wrote:
> >>>>>> Commit 068c29a248b6 ("PCI/ERR: Clear PCIe Device Status errors only if
> >>>>>> OS owns AER") adds support to clear error status in the Device Status
> >>>>>> Register(DEVSTA) only if OS owns the AER support. But this change
> >>>>>> breaks the requirement of the EDR feature which requires OS to cleanup
> >>>>>> the error registers even if firmware owns the control of AER support.

> ...
> > An EDR notification is issued on a bus device that is still present,
> > i.e., a DPC port or parent, but child devices have been disconnected
> > (ACPI v6.3, sec 5.6.6).
> 
> IMO, instead of bus device, we can call it as root port or down stream
> port. Please check the PCI firmware specification, r3.3, section 4.3.13.

Yeah, that makes sense.  I just used the "bus device" language because
that's what's in the ACPI spec.  But I think the PCI terms would
probably be more helpful here.  And I'll cite the r6.5 spec instead of
v6.3.

> Firmware may wish to issue Error Disconnect Recover notification on a port
> that is parent of the port that experienced the containment event.
> 
> So it is either a downstream port or a root port.

Right.

> > That box *does* suggest clearing the port error status before bringing
> > the port out of DPC, and we're doing it in the opposite order:
> > 
> >   edr_handle_event(pdev)
> >     edev = acpi_dpc_port_get(pdev)
> >     # Both pdev and edev are present; pdev is same as edev or a
> >     # parent of edev; children of edev are disconnected
> >     dpc_process_error(edev)
> >     pcie_do_recovery(edev, dpc_reset_link)
> >       if (state == pci_channel_io_frozen)
> >         dpc_reset_link                  # (reset_subordinates)
> >           pci_write_config_word(PCI_EXP_DPC_STATUS_TRIGGER) # exit DPC
> >       if (AER native)
> >         pcie_clear_device_status(edev)
> >           clear PCI_EXP_DEVSTA          # doesn't happen
> >     if (PCI_ERS_RESULT_RECOVERED)
> >       pcie_clear_device_status
> >         clear PCI_EXP_DEVSTA            # added by this patch
> > 
> > Does it matter?  I dunno, but I don't *think* so.  We really don't
> > care about the value of PCI_EXP_DEVSTA anywhere except
> > pci_wait_for_pending_transaction(), which isn't applicable here.  And
> > I don't think the fact that it probably has an Error Detected bit set
> > when exiting DPC is a problem.
> 
> Agree that it is not a fatal issue. But leaving the stale error state
> is something that needs to be fixed.

Definitely agree we should clear the stale state.  I just meant that I
don't think it matters that we clear the status *after* exiting DPC,
instead of clearing it before exiting DPC as shown in the flowchart.

Bjorn