[PATCH V9 1/2] PCI: handle CRS returned by device after FLR

On Tue, Aug 08, 2017 at 08:57:24PM -0400, Sinan Kaya wrote:

Sporadic reset issues have been observed with Intel 750 NVMe drive by
writing to the reset file in sysfs in a loop. The sequence of events
observed is as follows:

- perform a Function Level Reset (FLR)
- sleep up to 1000ms total
- read ~0 from PCI_COMMAND
- warn that the device didn't return from FLR
- touch the device before it's ready

An endpoint is allowed to issue Configuration Request Retry Status (CRS)
following a FLR request to indicate that it is not ready to accept new
requests. CRS is defined in PCIe r3.1, sec 2.3.1. Request Handling Rules
and CRS usage in FLR context is mentioned in PCIe r3.1a, sec 6.6.2.
Function-Level Reset.

Don't we have a similar issue for other types of reset?  I would think
conventional reset, e.g., using secondary bus reset, hotplug slot
power, power management, etc., would have the same situation where a
device might return CRS status.