[PATCH v2 0/1] nvme: Fix problem when booting from NVMe drive was leading to a hang.

[Keith Busch]

On Tue, Mar 05, 2024 at 02:51:00PM +0100, Christoph Hellwig wrote:
> > +	/*
> > +	 * On certain host architectures/HW, DRAM was keeping memory contents over reboot-cycles.
> > +	 * It was observed that certain controllers were accessing host memory after
> > +	 * resetting which led to undefined state preventing proper initialization.
> > +	 */
> 
> Block comments should never span 80 characters.  But more importantly
> I don't even think we need this comment at all, this is a clear bug
> fix and the code is self-describing.

It sounds like a firmware bug. Spec says:

  "The host memory resources are not persistent in the controller across
   a reset event."

Exiting a shutdown state requires a CC.EN transition, which is a reset
event.

It still may be good practice for the host driver to explicitly disable
host memory, but as I said last time, doing this in the shutdown path
deadlocks if the drive fails to produce a response, which is why we
removed it in the first place.