linux-kernel - Re: [PATCH 2/2] PCI: NVMe device specific reset quirk

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Message-ID: <20180723170812.177a7161@t450s.home>
Date:   Mon, 23 Jul 2018 17:08:12 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Keith Busch <keith.busch@...el.com>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org
Subject: Re: [PATCH 2/2] PCI: NVMe device specific reset quirk

On Mon, 23 Jul 2018 16:45:08 -0600
Keith Busch <keith.busch@...el.com> wrote:

> On Mon, Jul 23, 2018 at 04:24:31PM -0600, Alex Williamson wrote:
> > Take advantage of NVMe devices using a standard interface to quiesce
> > the controller prior to reset, including device specific delays before
> > and after that reset.  This resolves several NVMe device assignment
> > scenarios with two different vendors.  The Intel DC P3700 controller
> > has been shown to only work as a VM boot device on the initial VM
> > startup, failing after reset or reboot, and also fails to initialize
> > after hot-plug into a VM.  Adding a delay after FLR resolves these
> > cases.  The Samsung SM961/PM961 (960 EVO) sometimes fails to return
> > from FLR with the PCI config space reading back as -1.  A reproducible
> > instance of this behavior is resolved by clearing the enable bit in
> > the configuration register and waiting for the ready status to clear
> > (disabling the NVMe controller) prior to FLR.
> > 
> > As all NVMe devices make use of this standard interface and the NVMe
> > specification also requires PCIe FLR support, we can apply this quirk
> > to all devices with matching class code.  
> 
> Shouldn't this go in the nvme driver's reset_prepare/reset_done callbacks?

The scenario I'm trying to fix is device assignment, the nvme driver
isn't in play there.  The device is bound to the vfio-pci driver at the
time of these resets.  Thanks,

Alex