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Message-ID: <93D815E0-3100-4AAC-B9EE-AA6736A0419F@intel.com>
Date: Mon, 23 Nov 2020 23:57:35 +0000
From: "Kelley, Sean V" <sean.v.kelley@...el.com>
To: Bjorn Helgaas <helgaas@...nel.org>
CC: "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
"xerces.zhao@...il.com" <xerces.zhao@...il.com>,
"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
"Raj, Ashok" <ashok.raj@...el.com>,
"Luck, Tony" <tony.luck@...el.com>,
"Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@...el.com>,
"Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>,
Linux PCI <linux-pci@...r.kernel.org>,
"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v12 10/15] PCI/ERR: Limit AER resets in pcie_do_recovery()
Hi Bjorn,
> On Nov 23, 2020, at 3:28 PM, Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Fri, Nov 20, 2020 at 04:10:31PM -0800, Sean V Kelley wrote:
>> In some cases a bridge may not exist as the hardware controlling may be
>> handled only by firmware and so is not visible to the OS. This scenario is
>> also possible in future use cases involving non-native use of RCECs by
>> firmware.
>>
>> Explicitly apply conditional logic around these resets by limiting them to
>> Root Ports and Downstream Ports.
>
> Can you help me understand this? The subject says "Limit AER resets"
> and here you say "limit them to RPs and DPs", but it's not completely
> obvious how the resets are being limited, i.e., the patch doesn't add
> anything like:
>
> + if (type == PCI_EXP_TYPE_ROOT_PORT ||
> + type == PCI_EXP_TYPE_DOWNSTREAM)
> reset_subordinates(bridge);
>
> It *does* add checks around pcie_clear_device_status(), but that also
> includes RC_EC. And that's not a reset, so I don't think that's
> explicitly mentioned in the commit log.
The subject should have referred to the clearing of the device status rather than resets.
It originally came from this simpler patch in which I made use of reset instead of clear:
https://lore.kernel.org/linux-pci/20201002184735.1229220-8-seanvk.dev@oregontracks.org/
So a rephrase of clearing in place of resets would be more appropriate.
Then we added the notion of bridges…below
>
> Also see the question below.
>
>> Link: https://lore.kernel.org/r/20201002184735.1229220-8-seanvk.dev@oregontracks.org
>> Signed-off-by: Sean V Kelley <sean.v.kelley@...el.com>
>> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
>> Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
>> ---
>> drivers/pci/pcie/err.c | 31 +++++++++++++++++++++++++------
>> 1 file changed, 25 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>> index 8b53aecdb43d..7883c9791562 100644
>> --- a/drivers/pci/pcie/err.c
>> +++ b/drivers/pci/pcie/err.c
>> @@ -148,13 +148,17 @@ static int report_resume(struct pci_dev *dev, void *data)
>>
>> /**
>> * pci_walk_bridge - walk bridges potentially AER affected
>> - * @bridge: bridge which may be a Port
>> + * @bridge: bridge which may be a Port, an RCEC with associated RCiEPs,
>> + * or an RCiEP associated with an RCEC
>> * @cb: callback to be called for each device found
>> * @userdata: arbitrary pointer to be passed to callback
>> *
>> * If the device provided is a bridge, 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 has no subordinate bus, call the callback on the
>> + * device itself.
>> */
>> static void pci_walk_bridge(struct pci_dev *bridge,
>> int (*cb)(struct pci_dev *, void *),
>> @@ -162,6 +166,8 @@ static void pci_walk_bridge(struct pci_dev *bridge,
>> {
>> if (bridge->subordinate)
>> pci_walk_bus(bridge->subordinate, cb, userdata);
>> + else
>> + cb(bridge, userdata);
>> }
>>
>> pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>> @@ -174,10 +180,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>>
>> /*
>> * Error recovery runs on all subordinates of the bridge. If the
>> - * bridge detected the error, it is cleared at the end.
>> + * bridge detected the error, it is cleared at the end. For RCiEPs
>> + * we should reset just the RCiEP itself.
>> */
>> if (type == PCI_EXP_TYPE_ROOT_PORT ||
>> - type == PCI_EXP_TYPE_DOWNSTREAM)
>> + type == PCI_EXP_TYPE_DOWNSTREAM ||
>> + type == PCI_EXP_TYPE_RC_EC ||
>> + type == PCI_EXP_TYPE_RC_END)
>> bridge = dev;
>> else
>> bridge = pci_upstream_bridge(dev);
>> @@ -185,6 +194,12 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>> pci_dbg(bridge, "broadcast error_detected message\n");
>> if (state == pci_channel_io_frozen) {
>> pci_walk_bridge(bridge, report_frozen_detected, &status);
>> + if (type == PCI_EXP_TYPE_RC_END) {
>> + pci_warn(dev, "subordinate device reset not possible for RCiEP\n");
>> + status = PCI_ERS_RESULT_NONE;
>> + goto failed;
>> + }
>> +
>> status = reset_subordinates(bridge);
>> if (status != PCI_ERS_RESULT_RECOVERED) {
>> pci_warn(bridge, "subordinate device reset failed\n");
>> @@ -217,9 +232,13 @@ pci_ers_result_t pcie_do_recovery(struct pci_dev *dev,
>> pci_dbg(bridge, "broadcast resume message\n");
>> pci_walk_bridge(bridge, report_resume, &status);
>>
>> - if (pcie_aer_is_native(bridge))
>> - pcie_clear_device_status(bridge);
>> - pci_aer_clear_nonfatal_status(bridge);
>> + if (type == PCI_EXP_TYPE_ROOT_PORT ||
>> + type == PCI_EXP_TYPE_DOWNSTREAM ||
>> + type == PCI_EXP_TYPE_RC_EC) {
>> + if (pcie_aer_is_native(bridge))
>> + pcie_clear_device_status(bridge);
>> + pci_aer_clear_nonfatal_status(bridge);
>
> This is hard to understand because "type" is from "dev", but "bridge"
> is not necessarily the same device. Should it be this?
>
> type = pci_pcie_type(bridge);
> if (type == PCI_EXP_TYPE_ROOT_PORT ||
> ...)
Correct, it would be better if the type was based on the ‘bridge’.
Thanks,
Sean
>
>> + }
>> pci_info(bridge, "device recovery successful\n");
>> return status;
>>
>> --
>> 2.29.2
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