linux-kernel - Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for non-hotplug capable devices

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Message-ID: <7b15ffd4-ac9b-6753-63a7-dc6e2bfa30c8@linux.intel.com>
Date:   Wed, 27 May 2020 20:57:23 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Yicong Yang <yangyicong@...ilicon.com>, bhelgaas@...gle.com
Cc:     jay.vosburgh@...onical.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, ashok.raj@...el.com
Subject: Re: [PATCH v1 1/1] PCI/ERR: Handle fatal error recovery for
 non-hotplug capable devices



On 5/26/20 11:41 PM, Yicong Yang wrote:
>>> We should do slot reset if driver required, but it's different from the `slot reset` in pci_bus_error_reset().
>>> Previously we don't do a slot reset and call ->slot_reset() directly, I don't know the certain reason.
>> IIUC, your concern is whether it is correct to trigger reset for
>> pci_channel_io_normal case right ? Please correct me if my
>> assumption is incorrect.
> right.
> 
>> If its true, then why would report_error_detected() will return
>> PCI_ERS_*_NEED_RESET for pci_channel_io_normal case ? If
>> report_error_detected() requests reset in pci_channel_io_normal
>> case then I think we should give preference to it.
> If we get PCI_ERS_*_NEED_RESET, we should do slot reset, no matter it's a
> hotpluggable slot or not.

pci_slot_reset() function itself has dependency on hotplug ops. So
what kind of slot reset is needed for non-hotplug case?

static int pci_slot_reset(struct pci_slot *slot, int probe)
{
	int rc;

	if (!slot || !pci_slot_resetable(slot))
		return -ENOTTY;

	if (!probe)
		pci_slot_lock(slot);

	might_sleep();

	rc = pci_reset_hotplug_slot(slot->hotplug, probe);

	if (!probe)
		pci_slot_unlock(slot);

	return rc;
}

static int pci_reset_hotplug_slot(struct hotplug_slot *hotplug, int probe)
{
	int rc = -ENOTTY;

	if (!hotplug || !try_module_get(hotplug->owner))
		return rc;

	if (hotplug->ops->reset_slot)
		rc = hotplug->ops->reset_slot(hotplug, probe);

	module_put(hotplug->owner);

	return rc;
}
   And we shouldn't do it here in reset_link(), that's
> two separate things.  The `slot reset` done in aer_root_reset() is only for *link
> reset*, as there may have some side effects to perform secondary bus reset directly
> for hotpluggable slot, as mentioned in commit c4eed62a2143, so it use slot reset
> to do the reset link things.
> 
> As for slot reset required by the driver, we should perform it later just before the
> ->slot_reset(). I noticed the TODO comments there and we should implement
> it if it's necessary.
I agree.
> 
> It lies in line 183, drivers/pcie/err.c:
> 
>      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);
>      }
> 
>