[PATCH v2 4/4] PCI/AER: Dont do recovery when DPC is enabled

quoted

Whether the AER driver reads ~0 or not really depends on timing. The
link may come up from the DPC driver by the time AER driver reaches
here as an example.

Bad things do happen. We have seen this with e1000e driver.

I don't doubt that bad things happen.  I'm just trying to understand
exactly *what* bad things happen and how, so we can fix them cleanly.

This was random crashes in the e1000e drivers accompanied with stack
traces coming from WARN and msi allocation routines.

I don't know exactly what you mean by "DPC stops the drivers
immediately".  Since the DPC hardware disables the Link, I *think*
you probably mean that driver accesses to the device start failing
(whether the driver notices this is a whole different question).

Sorry for not being clear.

I was talking about the pci_stop_and_remove_bus_device() call in DPC's
interrupt_event_handler() function as the "stop command".

When the DPC hardware disables the Link, it causes a hot reset for
downstream components.  The DPC interrupt_event_handler() doesn't do
much except remove the device (which detaches the driver) and clear
the DPC Trigger Status bit (which allows hardware to try to retrain
the Link).

That's true.

So the "stop" and "recover" commands you mention must be related to
AER.  

I was talking about pci_stop_and_remove_bus_device() vs. error_detected()
as "stop" and "recover"

I guess these would be some of the driver callbacks
(error_detected(), mmio_enabled(), slot_reset(), reset_prepare(),
reset_done(), resume())?

In any case, I agree that it probably doesn't make sense to call any
of these callbacks if the DPC driver has already detached the driver
and re-attached it.  The device state is gone because of the hot reset
and the driver state is gone because of the detach/re-attach.

However, I'm not so sure about the period *before* the DPC driver
detaches the driver.  The description of error_detected() says it
cannot assume the device is accessible, so I think there might be an
argument that AER *should* call this for DPC events so the driver has
a chance to clean up before being unceremoniously detached.

Makes sense. Let us work on this.

I suspect this all probably requires tighter integration between DPC
and AER, and I'm totally fine with that.  I think the current
separation as separate "drivers" is pretty artificial anyway.

Got it. We will try to plumb DPC error handling into AER driver's error
handling mechanism.

Another question:

What do you think about the rescan following link up? The only entity
that does rescan today is hotplug after DPC recovery. There could be
a platform with DPC support but no hotplug support. 

How should we handle it?

We can call rescan from DPC all the time.

-- 
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.