Re: [PATCH v2 0/4] Address error and recovery for AER and DPC

[Bjorn Helgaas]

On Fri, Dec 29, 2017 at 12:54:15PM +0530, Oza Pawandeep wrote:
> This patch set brings in support for DPC and AER to co-exist and not to
> race for recovery.
> 
> The current implementation of AER and error message broadcasting to the
> EP driver is tightly coupled and limited to AER service driver.
> It is important to factor out broadcasting and other link handling
> callbacks. So that not only when AER gets triggered, but also when DPC get
> triggered, or both get triggered simultaneously (for e.g. ERR_FATAL),
> callbacks are handled appropriately.
> having modularized the code, the race between AER and DPC is handled
> gracefully.
> for e.g. when DPC is active and kicked in, AER should not attempt to do
> recovery, because DPC takes care of it.

High-level question:

We have some convoluted code in negotiate_os_control() and
aer_service_init() that (I think) essentially disables AER unless the
platform firmware grants us permission to use it.

The last implementation note in PCIe r3.1, sec 6.2.10 says

  DPC may be controlled in some configurations by platform firmware
  and in other configurations by the operating system. DPC
  functionality is strongly linked with the functionality in Advanced
  Error Reporting. To avoid conflicts over whether platform firmware
  or the operating system have control of DPC, it is recommended that
  platform firmware and operating systems always link the control of
  DPC to the control of Advanced Error Reporting.

I read that as suggesting that we should enable DPC support in Linux
if and only if we also enable AER.  But I don't see anything in DPC
that looks like that.  Should there be something there?  Should DPC be
restructured so it's enabled and handled inside the AER driver instead
of being a separate driver?

Bjorn