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

[Michael Kropaczek]

Thank you, Keith, Christoph,

The comment will be removed in the next version,

   Michael

-----Original Message-----
From: Keith Busch <kbusch at kernel.org> 
Sent: Tuesday, March 5, 2024 7:18 AM
To: Christoph Hellwig <hch at lst.de>
Cc: Michael Kropaczek <Michael.Kropaczek at solidigm.com>; linux-nvme at lists.infradead.org; Jens Axboe <axboe at fb.com>; Sagi Grimberg <sagi at grimberg.me>
Subject: Re: [PATCH v2 0/1] nvme: Fix problem when booting from NVMe drive was leading to a hang.

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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.