linux-kernel - RE: [PATCH v3 00/27] Add support for OpenCAPI Persistent Memory devices

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Date:   Wed, 26 Feb 2020 11:35:25 +1100
From:   "Alastair D'Silva" <alastair@....ibm.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     "Oliver O'Halloran" <oohall@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Frederic Barrat <fbarrat@...ux.ibm.com>,
        Andrew Donnellan <ajd@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>,
        Anton Blanchard <anton@...abs.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
        Cédric Le Goater <clg@...d.org>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kurz <groug@...d.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux MM <linux-mm@...ck.org>
Subject: RE: [PATCH v3 00/27] Add support for OpenCAPI Persistent Memory devices

On Tue, 2020-02-25 at 16:32 -0800, Dan Williams wrote:
> On Tue, Feb 25, 2020 at 4:14 PM Alastair D'Silva <
> alastair@....ibm.com> wrote:
> > On Mon, 2020-02-24 at 17:51 +1100, Oliver O'Halloran wrote:
> > > On Mon, Feb 24, 2020 at 3:43 PM Alastair D'Silva <
> > > alastair@....ibm.com> wrote:
> > > > On Sun, 2020-02-23 at 20:37 -0800, Matthew Wilcox wrote:
> > > > > On Mon, Feb 24, 2020 at 03:34:07PM +1100, Alastair D'Silva
> > > > > wrote:
> > > > > > V3:
> > > > > >   - Rebase against next/next-20200220
> > > > > >   - Move driver to arch/powerpc/platforms/powernv, we now
> > > > > > expect
> > > > > > this
> > > > > >     driver to go upstream via the powerpc tree
> > > > > 
> > > > > That's rather the opposite direction of normal; mostly
> > > > > drivers
> > > > > live
> > > > > under
> > > > > drivers/ and not in arch/.  It's easier for drivers to get
> > > > > overlooked
> > > > > when doing tree-wide changes if they're hiding.
> > > > 
> > > > This is true, however, given that it was not all that desirable
> > > > to
> > > > have
> > > > it under drivers/nvdimm, it's sister driver (for the same
> > > > hardware)
> > > > is
> > > > also under arch, and that we don't expect this driver to be
> > > > used on
> > > > any
> > > > platform other than powernv, we think this was the most
> > > > reasonable
> > > > place to put it.
> > > 
> > > Historically powernv specific platform drivers go in their
> > > respective
> > > subsystem trees rather than in arch/ and I'd prefer we kept it
> > > that
> > > way. When I added the papr_scm driver I put it in the pseries
> > > platform
> > > directory because most of the pseries paravirt code lives there
> > > for
> > > some reason; I don't know why. Luckily for me that followed the
> > > same
> > > model that Dan used when he put the NFIT driver in drivers/acpi/
> > > and
> > > the libnvdimm core in drivers/nvdimm/ so we didn't have anything
> > > to
> > > argue about. However, as Matthew pointed out, it is at odds with
> > > how
> > > most subsystems operate. Is there any particular reason we're
> > > doing
> > > things this way or should we think about moving libnvdimm users
> > > to
> > > drivers/nvdimm/?
> > > 
> > > Oliver
> > 
> > I'm not too fussed where it ends up, as long as it ends up
> > somewhere :)
> > 
> > From what I can tell, the issue is that we have both
> > "infrastructure"
> > drivers, and end-device drivers. To me, it feels like
> > drivers/nvdimm
> > should contain both, and I think this feels like the right
> > approach.
> > 
> > I could move it back to drivers/nvdimm/ocxl, but I felt that it was
> > only tolerated there, not desired. This could be cleared up with a
> > response from Dan Williams, and if it is indeed dersired, this is
> > my
> > preferred location.
> 
> Apologies if I gave the impression it was only tolerated. I'm ok with
> drivers/nvdimm/ocxl/, and to the larger point I'd also be ok with a
> drivers/{acpi => nvdimm}/nfit and {arch/powerpc/platforms/pseries =>
> drivers/nvdimm}/papr_scm.c move as well to keep all the consumers of
> the nvdimm related code together with the core.

Great, thanks for clarifying, text is so imprecise when it comes to
nuance :)

I'll move ti back to drivers/nvdimm/ocxl then.

-- 
Alastair D'Silva
Open Source Developer
Linux Technology Centre, IBM Australia
mob: 0423 762 819