Re: [PATCH] nvme-pci: Prevent mmio reads if pci channel offline

From: Keith Busch
Date: Thu Feb 28 2019 - 19:30:20 EST

On Thu, Feb 28, 2019 at 11:43:46PM +0000, Austin.Bolen@xxxxxxxx wrote:
> On 2/28/2019 5:20 PM, Keith Busch wrote:
> > SBR and Link Disable are done from the down stream port, though, so the
> > host can still communicate with the function that took the link down.
> > That's entirely different than taking the link down from the end device,
> > so I'm not sure how NVMe can fix that.
> >
> Agreed it is different. Here is one way they could have solved it: host
> writes magic value to NSSRC but device latches this instead of
> resetting. Then require host to do SBR. When device sees SBR with
> magic value in NSSRC it does an NSSR.

For single port drives, yes, but that wouldn't work so well for multi-port
devices connected to different busses, maybe even across multiple hosts.
The equivalent of an FLR across all ports should have been sufficient,