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

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Date:   Mon, 24 Feb 2020 17:51:33 +1100
From:   "Oliver O'Halloran" <oohall@...il.com>
To:     "Alastair D'Silva" <alastair@....ibm.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        "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 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