On Thu, 2 Jul 2020 11:06:26 -0700
Sean V Kelley <sean.v.kelley@xxxxxxxxxxxxxxx> wrote:
> On 26 Jun 2020, at 11:41, Jonathan Cameron wrote:
>
> > On Fri, 26 Jun 2020 09:29:34 -0700
> > Sean V Kelley <sean.v.kelley@xxxxxxxxxxxxxxx> wrote:
> >
> >> Hi,
> > Hi,
> >
> > Thanks for taking a look.
> >
> >>
> >>
> >> On 22 Jun 2020, at 4:44, Jonathan Cameron wrote:
> >>
> >>> Was previously: PCI/AER: Add partial initial supprot for RCiEPs
> >>> using
> >>> RCEC or
> >>> firmware first.
> >>>
> >>> Currently the kernel does not handle AER errors for Root Complex
> >>> integrated
> >>> End Points (RCiEPs)[0]. These devices sit on a root bus within the
> >>> Root Complex
> >>> (RC). AER handling is performed by a Root Complex Event Collector
> >>> (RCEC) [1]
> >>> which is a effectively a type of RCiEP on the same root bus.
> >>>
> >>> This code will only perform the correct reset flow for the case
> >>> where
> >>> there
> >>> is no need to take any actions on the RCEC because the firmware is
> >>> responsible for them. This is true where APEI [2] is used to
> >>> report
> >>> the AER
> >>> errors via a GHES[v2] HEST entry [3] and relevant AER CPER record
> >>> [4]
> >>> and Firmware
> >>> First handling is in use.
> >>
> >> Right, in the case of the RCEC one identifies the RCiEPs by the RCiEP
> >> bitmap as a part of the RCEC Associated Endpoint Extended
> >> Capabilities.
> >> This ‘search’ so to speak would make use also of the RCEC
> >> Associated
> >> Bus Numbers Register to associate the devices with an RCEC when not
> >> on
> >> the same bus.
> >
> > Ah. I'm afraid my access to recent specs is a bit limited at the
> > moment.
> > I do have a draft 5.0 spec which has that in though so I now see what
> > you mean.
> >
> > Was introduced in Root Complex Event Collector Endpoint Association
> > Extended
> > Capability version 2 in PCIe 5.0 I think.
> >
>
> Correct.
>
> >>
> >>>
> >>> As there is no current RCEC driver support, it should not be
> >>> possible
> >>> to get
> >>> to this code via any routes other than the one above. Hence
> >>> appropriate RCEC
> >>> handling can be added when the RCEC driver support is ready.
> >>
> >>
> >>>
> >>> The error handling is different from a normal PCIe End Point
> >>> because:
> >>>
> >>> 1) There is no downstream port above an RCiEP as these devices sit
> >>> on
> >>> a root
> >>> bus.
> >>>
> >>> 2) In general, it makes little sense to reset other devices on on
> >>> the
> >>> same
> >>> root bus. For error handling outside the of the root complex
> >>> (RC)
> >>> an AER
> >>> error will indicate that all the topology below the physical
> >>> link,
> >>> which
> >>> the error is related to, will need to be reset as they share a
> >>> common
> >>> path to the host. For an RCiEP there is no such defined shared
> >>> path
> >>> relationship with other elements on the root bus.
> >>>
> >>> A new walk function, similar to pci_bus_walk is provided that takes
> >>> a
> >>> pci_dev
> >>> instead of a bus. If that dev corresponds to a downstream port it
> >>> will walk
> >>> the subordinate bus of that downstream port. If the dev does not
> >>> then
> >>> it
> >>> will call the function on that device alone. This function allows
> >>> us
> >>> to
> >>> avoid adding special cases to the majority of the error handling.
> >>
> >> Then in that case the callback could add the additional checks
> >> specific
> >> to identifying the associated RCiEPs.
> >
> > I am afraid I don't follow what you mean here. Could you give more
> > info?
>
> Sure, a given RCEC can be associated with multiple RCiEPs. As a part of
> the Extended Association Cap it is possible to obtain a bitmap of the
> RCiEP device ids on the same bus number as the RCEC device itself.
> (5.0-1.0 sec 7.9.10.2). With a Cap version of 2h or higher, it is also
> possible to get an additional range of bus numbers containing RCiEPs
> also associated with this RCEC.
>
> So I’m wondering if this function could be used in which passing a
> dev, in this case the RCEC, triggers the call back which makes use of
> the RCiEP bitmap and associated bus ranges to return all identified
> devices in use cases such as in AER for finding sources, etc.
Ah understood.
If we do this we effectively end up with 3 different types of walk and
the meaning of the walk function gets more complex again.
1) Normal bus walk - we pass the downstream port above a bus to which
the device is attached and it walks everthing below that point.
2) Case I care about RCiEP with no visible association with an RCEC as
I don't need to walk devices. In that case just calls the callbacks for
the actual device.
3) Pass in RCiEP with RCEC asociated with it (or do a dance at the caller
to pass in the RCEC itself). Need to walk the devices that the RCEC is
handling errors for. For handling, I'm not all the calls will be generally
applicable to other devices associated with the RCEC as some only make
sense if there is an actual PCIe bus involved and hence we need to reset
other devices on that bus. For RCEC I don't think there is an particular
reason to assume an AER error reported at one RCiEP will have any impact
on other devices associated with the particular RCEC.
I've not found anything in the spec addressing this question but perhaps
I've missed something?
However, if the RCEC doesn't support multiple error records, you may need
to walk the bus to identify multiple simultaneous issues, very carefully
avoiding (or least minimizing) race conditions.
>
> The alternative is to have a separate walk for RCECs that loops through
> the bitmap / ranges (if supported) triggering the callback for each
> device found.
Agreed. We would end up with the same splitting of handling paths that
wasn't liked in my v1 patch. Perhaps we need single pci_walk_aer_affected
function with a pile of documentation for what it is actually doing?
Even then we may need to have a parameter to indicate a particular callback
should be restricted to devices that share a 'real bus' or not.
I guess the proof will as ever be in what the code looks like.
Hmm. It increasingly feels like we may need to have a go at drawing together
some coherent documentation for the different ways of handling
AER errors and specifications / assumptions for each. Would be 'interesting'
to do given I'm fairly sure very few people actually understands all the options and
nasty corner cases!
+CC Lorenzo and James who may also be interested in this topic in general.
Thanks,
Jonathan
>
> Thanks,
>
> Sean
>
> >>
> >>>
> >>> Open questions:
> >>>
> >>> 1. Are we better protecting against link reset for an RCiEP in here
> >>> or
> >>> should we put the check in the link reset functions?
> >>>
> >>> 2. If we were to get a stupid firmware record with the relevant
> >>> reset
> >>> flag
> >>> set to trigger a link reset, what is the correct response? For
> >>> now
> >>> I
> >>> try to report that we haven't done anything and print a warning.
> >>>
> >>> 3. Naming of pci_walk_below_dev is rather unsatisfying. Any better
> >>> ideas?
> >>>
> >>> 4. pci_walk_below_dev is perhaps not of general utility. Shall I
> >>> make
> >>> it local
> >>> in err.c? If not would a precursor patch for that be
> >>> preferred?’
> >>
> >> It depends. Is it intended as a drop in replacement where needed for
> >> pci_walk_bus()? So in that case you are now passing the dev structure
> >> and do the check for subordinate or is it intended as being specific
> >> to
> >> say RCEC? With AER, one could either first check for RC_EC type
> >> before
> >> using this one. Or one could just drop in replace (passing the dev
> >> structure instead) and the call back performs the RCEC specific
> >> checks
> >> when a device is encountered.
> >
> > If it is useful in aer.c that's great. Just seemed such a weird
> > beast
> > I wasn't sure it would be of use anywhere else.
> >
> >>
> >>>
> >>> Testing has been performed via error injection on a QEMU platform as
> >>> that lets
> >>> me create a wide range of topologies and report errors at any chosen
> >>> location.
> >>> Currently I have no plans to upstream this injection support, but am
> >>> happy to
> >>> share if useful to others.
> >>
> >> I’m experimenting with it in my RCEC code in AER and will give you
> >> additional feedback.
> >
> > Great, thanks
> >
> > Jonathan
> >
> >>
> >> Thanks,
> >>
> >> Sean
> >>
> >>
> >>>
> >>> [0] ACPI PCI Express Base Specification 4.0 1.3.2.3 Root Complex
> >>> Integrated
> >>> Endpoint Rules.
> >>> [1] ACPI PCI Express Base Specification 4.0 6.2 Error Signalling and
> >>> Logging
> >>> [2] ACPI Specification 6.3 Chapter 18 ACPI Platform Error Interface
> >>> (APEI)
> >>> [3] ACPI Sepcification 6.3 18.2.3.7 Generic Hardware Error Source
> >>> [4] UEFI Specification 2.8, N.2.7 PCI Express Error Section
> >>>
> >>> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> >>> ---
> >>> Changes since v1:
> >>> * Separated from the largely unrelated fix so the two can move
> >>> forwards separately.
> >>> * Instead of separate path for RCiEP handling use the method
> >>> suggested
> >>> by Bjorn
> >>> and Sathyanarayanan with an adjusted pci_bus_walk.
> >>>
> >>> Thanks all for reviews of V1.
> >>>
> >>> drivers/pci/bus.c | 28 ++++++++++++++++++++++++++++
> >>> drivers/pci/pcie/err.c | 29 +++++++++++++++++++----------
> >>> include/linux/pci.h | 2 ++
> >>> 3 files changed, 49 insertions(+), 10 deletions(-)
> >>>
> >>> diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c
> >>> index 8e40b3e6da77..7cbe1ed2db3d 100644
> >>> --- a/drivers/pci/bus.c
> >>> +++ b/drivers/pci/bus.c
> >>> @@ -411,6 +411,34 @@ void pci_walk_bus(struct pci_bus *top, int
> >>> (*cb)(struct pci_dev *, void *),
> >>> }
> >>> EXPORT_SYMBOL_GPL(pci_walk_bus);
> >>>
> >>> +/** pci_walk_below_dev - walk devices below (or on) another device
> >>> + * @dev device for which we should walk below, include device
> >>> when not a port.
> >>> + * @cb callback to be called for each device found
> >>> + * @userdata arbitrary pointer to be passed to callback.
> >>> + *
> >>> + * If the device provided is a port,
> >>> + * walk the subordinate bus, including any bridged devices
> >>> + * on buses under this bus. Call the provided callback
> >>> + * on each device found.
> >>> + *
> >>> + * If the device provided hs no subordinate bus, call the provided
> >>> + * callback on the device itself.
> >>> + *
> >>> + */
> >>> +void pci_walk_below_dev(struct pci_dev *dev, int (*cb)(struct
> >>> pci_dev
> >>> *, void *),
> >>> + void *userdata)
> >>> +{
> >>> + struct pci_bus *bus;
> >>> +
> >>> + if (dev->subordinate) {
> >>> + bus = dev->subordinate;
> >>> + pci_walk_bus(bus, cb, userdata);
> >>> + } else {
> >>> + cb(dev, userdata);
> >>> + }
> >>> +}
> >>> +EXPORT_SYMBOL_GPL(pci_walk_below_dev);
> >>> +
> >>> struct pci_bus *pci_bus_get(struct pci_bus *bus)
> >>> {
> >>> if (bus)
> >>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
> >>> index 14bb8f54723e..fa08b1cc3d96 100644
> >>> --- a/drivers/pci/pcie/err.c
> >>> +++ b/drivers/pci/pcie/err.c
> >>> @@ -151,33 +151,39 @@ pci_ers_result_t pcie_do_recovery(struct
> >>> pci_dev
> >>> *dev,
> >>> pci_ers_result_t (*reset_link)(struct pci_dev *pdev))
> >>> {
> >>> pci_ers_result_t status = PCI_ERS_RESULT_CAN_RECOVER;
> >>> - struct pci_bus *bus;
> >>>
> >>> /*
> >>> * Error recovery runs on all subordinates of the first downstream
> >>> port.
> >>> * If the downstream port detected the error, it is cleared at the
> >>> end.
> >>> + * For RCiEPs we should reset just the RCiEP itself.
> >>> */
> >>> if (!(pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
> >>> - pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM))
> >>> + pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM ||
> >>> + pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END))
> >>> dev = dev->bus->self;
> >>> - bus = dev->subordinate;
> >>>
> >>> pci_dbg(dev, "broadcast error_detected message\n");
> >>> if (state == pci_channel_io_frozen) {
> >>> - pci_walk_bus(bus, report_frozen_detected, &status);
> >>> + pci_walk_below_dev(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;
> >>> }
> >>> } else {
> >>> - pci_walk_bus(bus, report_normal_detected, &status);
> >>> + pci_walk_below_dev(dev, report_normal_detected, &status);
> >>> }
> >>>
> >>> if (status == PCI_ERS_RESULT_CAN_RECOVER) {
> >>> status = PCI_ERS_RESULT_RECOVERED;
> >>> pci_dbg(dev, "broadcast mmio_enabled message\n");
> >>> - pci_walk_bus(bus, report_mmio_enabled, &status);
> >>> + pci_walk_below_dev(dev, report_mmio_enabled, &status);
> >>> }
> >>>
> >>> if (status == PCI_ERS_RESULT_NEED_RESET) {
> >>> @@ -188,17 +194,20 @@ pci_ers_result_t pcie_do_recovery(struct
> >>> pci_dev
> >>> *dev,
> >>> */
> >>> status = PCI_ERS_RESULT_RECOVERED;
> >>> pci_dbg(dev, "broadcast slot_reset message\n");
> >>> - pci_walk_bus(bus, report_slot_reset, &status);
> >>> + pci_walk_below_dev(dev, report_slot_reset, &status);
> >>> }
> >>>
> >>> if (status != PCI_ERS_RESULT_RECOVERED)
> >>> goto failed;
> >>>
> >>> pci_dbg(dev, "broadcast resume message\n");
> >>> - pci_walk_bus(bus, report_resume, &status);
> >>> + pci_walk_below_dev(dev, report_resume, &status);
> >>>
> >>> - pci_aer_clear_device_status(dev);
> >>> - pci_aer_clear_nonfatal_status(dev);
> >>> + if ((pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT ||
> >>> + pci_pcie_type(dev) == PCI_EXP_TYPE_DOWNSTREAM)) {
> >>> + pci_aer_clear_device_status(dev);
> >>> + pci_aer_clear_nonfatal_status(dev);
> >>> + }
> >>> pci_info(dev, "device recovery successful\n");
> >>> return status;
> >>>
> >>> diff --git a/include/linux/pci.h b/include/linux/pci.h
> >>> index c79d83304e52..538bf0a76d33 100644
> >>> --- a/include/linux/pci.h
> >>> +++ b/include/linux/pci.h
> >>> @@ -1411,6 +1411,8 @@ int pci_scan_bridge(struct pci_bus *bus,
> >>> struct
> >>> pci_dev *dev, int max,
> >>>
> >>> void pci_walk_bus(struct pci_bus *top, int (*cb)(struct pci_dev *,
> >>> void *),
> >>> void *userdata);
> >>> +void pci_walk_below_dev(struct pci_dev *dev, int (*cb)(struct
> >>> pci_dev
> >>> *, void *),
> >>> + void *userdata);
> >>> int pci_cfg_space_size(struct pci_dev *dev);
> >>> unsigned char pci_bus_max_busnr(struct pci_bus *bus);
> >>> void pci_setup_bridge(struct pci_bus *bus);
> >>> --
> >>> 2.19.1
