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SubjectRe: [PATCH V5 3/3] PCI: Mask and unmask hotplug interrupts during reset
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On 7/3/2018 10:34 AM, Lukas Wunner wrote:
> On Mon, Jul 02, 2018 at 06:52:47PM -0400, Sinan Kaya wrote:
>> @@ -308,8 +310,17 @@ void pcie_do_fatal_recovery(struct pci_dev *dev, u32 service)
>> pci_dev_put(pdev);
>> }
>>
>> + hpsvc = pcie_port_find_service(udev, PCIE_PORT_SERVICE_HP);
>> + hpdev = pcie_port_find_device(udev, PCIE_PORT_SERVICE_HP);
>> +
>> + if (hpdev && hpsvc)
>> + hpsvc->mask_irq(to_pcie_device(hpdev));
>> +
>> result = reset_link(udev, service);
>>
>> + if (hpdev && hpsvc)
>> + hpsvc->unmask_irq(to_pcie_device(hpdev));
>> +
>
> We've already got the ->reset_slot callback in struct hotplug_slot_ops,
> I'm wondering if we really need additional ones for this use case.
>
> If you just do...
>
> if (!pci_probe_reset_slot(dev->slot))
> pci_reset_slot(dev->slot)
> else {
> /* regular code path */
> }
>
> would that not be equivalent?

As I have informed you before on my previous reply, the pdev->slot is
only valid for children objects such as endpoints not for a bridge when
using pciehp.

The pointer is NULL for the host bridge itself.

I reached out to reset_slot() callback in v4 of this implementation.

https://patchwork.kernel.org/patch/10494971/

However, as Oza explained FATAL error handling gets called from two different
paths as AER and DPC.

If the link goes down due to DPC, calling pci_reset_slot() would be a mistake
as DPC has its own recovery mechanism by programming the DPC capabilities.
pci_reset_slot() performs a secondary bus reset following hotplug interrupt
mask.

Issuing a secondary bus reset to a DPC event would be a mistake for recovery.

That's why, I extracted the hotplug mask and unmask IRQ calls into service
layer so that I can mask hotplug interrupts regardless of the source of the
FATAL error whether it is DPC or AER.

If error source is DPC, it still goes to DPC driver's reset_link() callback
for DPC specific clean up.

If error source is AER, it still goes to AER driver's reset_link() callback
for secondary bus reset.

Remember that AER driver completely bypasses pci_reset_slot() today. The lock
mechanism you are putting will not be useful for FATAL error case where
pci_secondary_bus_reset() is called directly.

pci_reset_slot() only gets called from external drivers such as VFIO to initiate
a reset to the slot if hotplug is supported.

>
> (It's worth noting though that pciehp is the only hotplug driver
> implementing the ->reset_slot callback. If hotplug is handled by
> a different driver or by the platform firmware, devices may still
> be removed and re-enumerated twice.)
>
> Thanks,
>
> Lukas
>


--
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

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