Re: [PATCH v9 12/15] PCI/RCEC: Add RCiEP's linked RCEC to AER/ERR

Kuppuswamy, Sathyanarayanan
2020-10-17T05:31:59Z

On 10/16/20 3:29 PM, Bjorn Helgaas wrote:
> [+cc Christoph, Ethan, Sinan, Keith; sorry should have cc'd you to
> begin with since you're looking at this code too. Particularly
> interested in your thoughts about whether we should be touching
> PCI_ERR_ROOT_COMMAND and PCI_ERR_ROOT_STATUS when we don't own AER.]
This part is not very clear in ACPI spec or PCI firmware spec.

IMO, since AEPI notifies the OS about the error, then I guess
we are allowed to clear the PCI_ERR_ROOT_STATUS register
after handling the error.

>
> On Fri, Oct 16, 2020 at 03:30:37PM -0500, Bjorn Helgaas wrote:
>> [+to Jonathan]
>>
>> On Thu, Oct 15, 2020 at 05:11:10PM -0700, Sean V Kelley wrote:
>>> From: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
>>>
>>> When attempting error recovery for an RCiEP associated with an RCEC device,
>>> there needs to be a way to update the Root Error Status, the Uncorrectable
>>> Error Status and the Uncorrectable Error Severity of the parent RCEC. In
>>> some non-native cases in which there is no OS-visible device associated
>>> with the RCiEP, there is nothing to act upon as the firmware is acting
>>> before the OS.
>>>
>>> Add handling for the linked RCEC in AER/ERR while taking into account
>>> non-native cases.
>>>
>>> Co-developed-by: Sean V Kelley <sean.v.kelley@intel.com>
>>> Link: https://lore.kernel.org/r/20201002184735.1229220-12-seanvk.dev@oregontracks.org
>>> Signed-off-by: Sean V Kelley <sean.v.kelley@intel.com>
>>> Signed-off-by: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
>>> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
>>> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>>> ---
>>> drivers/pci/pcie/aer.c | 53 ++++++++++++++++++++++++++++++------------
>>> drivers/pci/pcie/err.c | 20 ++++++++--------
>>> 2 files changed, 48 insertions(+), 25 deletions(-)
>>>
>>> diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
>>> index 65dff5f3457a..083f69b67bfd 100644
>>> --- a/drivers/pci/pcie/aer.c
>>> +++ b/drivers/pci/pcie/aer.c
>>> @@ -1357,27 +1357,50 @@ static int aer_probe(struct pcie_device *dev)
>>> */
>>> static pci_ers_result_t aer_root_reset(struct pci_dev *dev)
>>> {
>>> - int aer = dev->aer_cap;
>>> + int type = pci_pcie_type(dev);
>>> + struct pci_dev *root;
>>> + int aer = 0;
>>> + int rc = 0;
>>> u32 reg32;
>>> - int rc;
>>>
>>> + if (pci_pcie_type(dev) == PCI_EXP_TYPE_RC_END)
>> "type == PCI_EXP_TYPE_RC_END"
>>
>>> + /*
>>> + * The reset should only clear the Root Error Status
>>> + * of the RCEC. Only perform this for the
>>> + * native case, i.e., an RCEC is present.
>>> + */
>>> + root = dev->rcec;
>>> + else
>>> + root = dev;
>>>
>>> - /* Disable Root's interrupt in response to error messages */
>>> - pci_read_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, &reg32);
>>> - reg32 &= ~ROOT_PORT_INTR_ON_MESG_MASK;
>>> - pci_write_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, reg32);
>>> + if (root)
>>> + aer = dev->aer_cap;
>>>
>>> - rc = pci_bus_error_reset(dev);
>>> - pci_info(dev, "Root Port link has been reset\n");
>>> + if (aer) {
>>> + /* Disable Root's interrupt in response to error messages */
>>> + pci_read_config_dword(root, aer + PCI_ERR_ROOT_COMMAND, &reg32);
>>> + reg32 &= ~ROOT_PORT_INTR_ON_MESG_MASK;
>>> + pci_write_config_dword(root, aer + PCI_ERR_ROOT_COMMAND, reg32);
>> Not directly related to *this* patch, but my assumption was that in
>> the APEI case, the firmware should retain ownership of the AER
>> Capability, so the OS should not touch PCI_ERR_ROOT_COMMAND and
>> PCI_ERR_ROOT_STATUS.
>>
>> But this code appears to ignore that ownership. Jonathan, you must
>> have looked at this recently for 068c29a248b6 ("PCI/ERR: Clear PCIe
>> Device Status errors only if OS owns AER"). Do you have any insight
>> about this?
>>
>>> - /* Clear Root Error Status */
>>> - pci_read_config_dword(dev, aer + PCI_ERR_ROOT_STATUS, &reg32);
>>> - pci_write_config_dword(dev, aer + PCI_ERR_ROOT_STATUS, reg32);
>>> + /* Clear Root Error Status */
>>> + pci_read_config_dword(root, aer + PCI_ERR_ROOT_STATUS, &reg32);
>>> + pci_write_config_dword(root, aer + PCI_ERR_ROOT_STATUS, reg32);
>>>
>>> - /* Enable Root Port's interrupt in response to error messages */
>>> - pci_read_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, &reg32);
>>> - reg32 |= ROOT_PORT_INTR_ON_MESG_MASK;
>>> - pci_write_config_dword(dev, aer + PCI_ERR_ROOT_COMMAND, reg32);
>>> + /* Enable Root Port's interrupt in response to error messages */
>>> + pci_read_config_dword(root, aer + PCI_ERR_ROOT_COMMAND, &reg32);
>>> + reg32 |= ROOT_PORT_INTR_ON_MESG_MASK;
>>> + pci_write_config_dword(root, aer + PCI_ERR_ROOT_COMMAND, reg32);
>>> + }
>>> +
>>> + if ((type == PCI_EXP_TYPE_RC_EC) || (type == PCI_EXP_TYPE_RC_END)) {
>>> + if (pcie_has_flr(root)) {
>>> + rc = pcie_flr(root);
>>> + pci_info(dev, "has been reset (%d)\n", rc);
>>> + }
>>> + } else {
>>> + rc = pci_bus_error_reset(root);
>> Don't we want "dev" for both the FLR and pci_bus_error_reset()? I
>> think "root == dev" except when dev is an RCiEP. When dev is an
>> RCiEP, "root" is the RCEC (if present), and we want to reset the
>> RCiEP, not the RCEC.
>>
>>> + pci_info(dev, "Root Port link has been reset (%d)\n", rc);
>>> + }
>> There are a couple changes here that I think should be split out.
>>
>> Based on my theory that when firmware retains control of AER, the OS
>> should not touch PCI_ERR_ROOT_COMMAND and PCI_ERR_ROOT_STATUS, and any
>> updates to them would have to be done by firmware before we get here,
>> I suggested reordering this:
>>
>> - clear PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK
>> - do reset
>> - clear PCI_ERR_ROOT_STATUS (for APEI, presumably done by firmware?)
>> - enable PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK
>>
>> to this:
>>
>> - clear PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK
>> - clear PCI_ERR_ROOT_STATUS
>> - enable PCI_ERR_ROOT_COMMAND ROOT_PORT_INTR_ON_MESG_MASK
>> - do reset
>>
>> If my theory is correct, I think we should still reorder this, but:
>>
>> - It's a significant behavior change that deserves its own patch so
>> we can document/bisect/revert.
>>
>> - I'm not sure why we clear the PCI_ERR_ROOT_COMMAND error reporting
>> bits. In the new "clear COMMAND, clear STATUS, enable COMMAND"
>> order, it looks superfluous. There's no reason to disable error
>> reporting while clearing the status bits.
>>
>> The current "clear, reset, enable" order suggests that the reset
>> might cause errors that we should ignore. I don't know whether
>> that's the case or not. It dates from 6c2b374d7485 ("PCI-Express
>> AER implemetation: AER core and aerdriver"), which doesn't
>> elaborate.
>>
>> - Should we also test for OS ownership of AER before touching
>> PCI_ERR_ROOT_STATUS?
>>
>> - If we remove the PCI_ERR_ROOT_COMMAND fiddling (and I tentatively
>> think we *should* unless we can justify it), that would also
>> deserve its own patch. Possibly (1) remove PCI_ERR_ROOT_COMMAND
>> fiddling, (2) reorder PCI_ERR_ROOT_STATUS clearing and reset, (3)
>> test for OS ownership of AER (?), (4) the rest of this patch.
>>
>>> return rc ? PCI_ERS_RESULT_DISCONNECT : PCI_ERS_RESULT_RECOVERED;
>>> }
>>> diff --git a/drivers/pci/pcie/err.c b/drivers/pci/pcie/err.c
>>> index 7883c9791562..cbc5abfe767b 100644
>>> --- a/drivers/pci/pcie/err.c
>>> +++ b/drivers/pci/pcie/err.c
>>> @@ -148,10 +148,10 @@ 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, 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
>>> + * @bridge bridge which may be an RCEC with associated RCiEPs,
>>> + * or 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 bridge, walk the subordinate bus, including
>>> * any bridged devices on buses under this bus. Call the provided callback
>>> @@ -164,8 +164,14 @@ static void pci_walk_bridge(struct pci_dev *bridge,
>>> int (*cb)(struct pci_dev *, void *),
>>> void *userdata)
>>> {
>>> + /*
>>> + * In a non-native case where there is no OS-visible reporting
>>> + * device the bridge will be NULL, i.e., no RCEC, no Downstream Port.
>>> + */
>>> if (bridge->subordinate)
>>> pci_walk_bus(bridge->subordinate, cb, userdata);
>>> + else if (bridge->rcec)
>>> + cb(bridge->rcec, userdata);
>>> else
>>> cb(bridge, userdata);
>>> }
>>> @@ -194,12 +200,6 @@ 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");
>>> --
>>> 2.28.0
>>>
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer