linux-kernel - RE: [PATCH v2 00/13] mpt3sas driver NVMe support:

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Date:   Mon, 7 Aug 2017 19:26:34 +0530
From:   Kashyap Desai <kashyap.desai@...adcom.com>
To:     James Bottomley <James.Bottomley@...senpartnership.com>,
        Christoph Hellwig <hch@...radead.org>,
        Hannes Reinecke <hare@...e.de>
Cc:     Suganath Prabu Subramani <suganath-prabu.subramani@...adcom.com>,
        martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        Sathya Prakash Veerichetty <sathya.prakash@...adcom.com>,
        linux-kernel@...r.kernel.org,
        Chaitra Basappa <chaitra.basappa@...adcom.com>,
        Sreekanth Reddy <sreekanth.reddy@...adcom.com>,
        linux-nvme@...ts.infradead.org
Subject: RE: [PATCH v2 00/13] mpt3sas driver NVMe support:

> -----Original Message-----
> From: James Bottomley [mailto:James.Bottomley@...senPartnership.com]
> Sent: Saturday, August 05, 2017 8:12 PM
> To: Christoph Hellwig; Hannes Reinecke
> Cc: Suganath Prabu S; martin.petersen@...cle.com; linux-
> scsi@...r.kernel.org; Sathya.Prakash@...adcom.com;
> kashyap.desai@...adcom.com; linux-kernel@...r.kernel.org;
> chaitra.basappa@...adcom.com; sreekanth.reddy@...adcom.com; linux-
> nvme@...ts.infradead.org
> Subject: Re: [PATCH v2 00/13] mpt3sas driver NVMe support:
>
> On Sat, 2017-08-05 at 06:53 -0700, Christoph Hellwig wrote:
> > On Wed, Aug 02, 2017 at 10:14:40AM +0200, Hannes Reinecke wrote:
> > >
> > > I'm not happy with this approach.
> > > NVMe devices should _not_ appear as SCSI devices; this will just
> > > confuse matters _and_ will be incompatible with 'normal' NVMe
> > > devices.
> > >
> > > Rather I would like to see the driver to hook into the existing NVMe
> > > framework (which essentially means to treat the mpt3sas as a weird
> > > NVMe-over-Fabrics HBA), and expose the NVMe devices like any other
> > > NVMe HBA.
> >
> > That doesn't make any sense.  The devices behind the mpt adapter don't
> > look like NVMe devices at all for the hosts - there are no NVMe
> > commands or queues involved at all, they hide behind the same somewhat
> > leaky scsi abstraction as other devices behind the mpt controller.
>
> You might think about what we did for SAS: split the generic handler into
> two
> pieces, libsas for driving the devices, which mpt didn't need because of
> the fat
> firmware and the SAS transport class so mpt could at least show the same
> sysfs
> files as everything else for SAS devices.

 Ventura generation of controllers are adding connectivity of NVME
 drives seamlessly and protocol handling is in Firmware.
 Same as SCSI to ATA translation done in firmware, Ventura controller
 is doing SCSI to NVME translation and for end user protocol handling
 is abstracted.

 This product handles new Transport protocol (NVME) same as ATA and
 transport is abstracted for end user.

NVME pass-through related driver code, it is just a big tunnel for user
space application.
It is just a basic framework like SATA PASS-Through in existing mpt3sas
driver.

>
> Fortunately for NVMe it's very simple at the moment its just a couple of
> host
> files and wwid on the devices.
>
> James
>
>
> > The only additional leak is that the controller now supports NVMe-
> > like PRPs in additions to its existing two SGL formats.
> >