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From:   Tomasz Figa <tomasz.figa@gmail.com>
Date:   Thu, 2 May 2019 15:42:59 +0900
Message-ID: <CA+Ln22H4ua9Zuh4eKaWfHtqh8DieyiS=5s7wS6-TbmA5Dsop4A@mail.gmail.com>
Subject: Re: [PATCH 4/5] dt-binding: mtd: onenand/samsung: Add device tree support
To:     Boris Brezillon <boris.brezillon@collabora.com>
Cc:     Rob Herring <robh@kernel.org>,
        =?UTF-8?Q?Pawe=C5=82_Chmiel?= <pawel.mikolaj.chmiel@gmail.com>,
        Kyungmin Park <kyungmin.park@samsung.com>,
        bbrezillon@kernel.org, miquel.raynal@bootlin.com, richard@nod.at,
        David Woodhouse <dwmw2@infradead.org>,
        computersforpeace@gmail.com, marek.vasut@gmail.com,
        Mark Rutland <mark.rutland@arm.com>,
        linux-mtd@lists.infradead.org,
        linux-kernel <linux-kernel@vger.kernel.org>,
        devicetree <devicetree@vger.kernel.org>
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2019=E5=B9=B45=E6=9C=882=E6=97=A5(=E6=9C=A8) 15:36 Boris Brezillon <boris.b=
rezillon@collabora.com>:
>
> Hi Tomasz,
>
> On Thu, 2 May 2019 15:23:33 +0900
> Tomasz Figa <tomasz.figa@gmail.com> wrote:
>
> > 2019=E5=B9=B45=E6=9C=882=E6=97=A5(=E6=9C=A8) 10:54 Rob Herring <robh@ke=
rnel.org>:
> > >
> > > On Fri, Apr 26, 2019 at 06:42:23PM +0200, Pawe=C5=82 Chmiel wrote:
> > > > From: Tomasz Figa <tomasz.figa@gmail.com>
> > > >
> > > > This patch adds dt-bindings for Samsung OneNAND driver.
> > > >
> > > > Signed-off-by: Tomasz Figa <tomasz.figa@gmail.com>
> > > > Signed-off-by: Pawe=C5=82 Chmiel <pawel.mikolaj.chmiel@gmail.com>
> > > > ---
> > > >  .../bindings/mtd/samsung-onenand.txt          | 46 +++++++++++++++=
++++
> > > >  1 file changed, 46 insertions(+)
> > > >  create mode 100644 Documentation/devicetree/bindings/mtd/samsung-o=
nenand.txt
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/mtd/samsung-onenand.=
txt b/Documentation/devicetree/bindings/mtd/samsung-onenand.txt
> > > > new file mode 100644
> > > > index 000000000000..341d97cc1513
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/mtd/samsung-onenand.txt
> > > > @@ -0,0 +1,46 @@
> > > > +Device tree bindings for Samsung SoC OneNAND controller
> > > > +
> > > > +Required properties:
> > > > + - compatible : value should be either of the following.
> > > > +   (a) "samsung,s3c6400-onenand" - for onenand controller compatib=
le with
> > > > +       S3C6400 SoC,
> > > > +   (b) "samsung,s3c6410-onenand" - for onenand controller compatib=
le with
> > > > +       S3C6410 SoC,
> > > > +   (c) "samsung,s5pc100-onenand" - for onenand controller compatib=
le with
> > > > +       S5PC100 SoC,
> > > > +   (d) "samsung,s5pv210-onenand" - for onenand controller compatib=
le with
> > > > +       S5PC110/S5PV210 SoCs.
> > > > +
> > > > + - reg : two memory mapped register regions:
> > > > +   - first entry: control registers.
> > > > +   - second and next entries: memory windows of particular OneNAND=
 chips;
> > > > +     for variants a), b) and c) only one is allowed, in case of d)=
 up to
> > > > +     two chips can be supported.
> > > > +
> > > > + - interrupt-parent : phandle of interrupt controller to which the=
 OneNAND
> > > > +   controller is wired,
> > >
> > > This is implied and can be removed.
> > >
> > > > + - interrupts : specifier of interrupt signal to which the OneNAND=
 controller
> > > > +   is wired; should contain just one entry.
> > > > + - clock-names : should contain two entries:
> > > > +   - "bus" - bus clock of the controller,
> > > > +   - "onenand" - clock supplied to OneNAND memory.
> > >
> > > If the clock just goes to the OneNAND device, then it should be in th=
e
> > > nand device node rather than the controller node.
> > >
> >
> > (Trying hard to recall the details about this hardware.)
> > AFAIR the clock goes to the controller and the controller then feeds
> > it to the memory chips.
> >
> > Also I don't think we should have any nand device nodes here, since
> > the memory itself is only exposed via the controller, which offers
> > various queries to probe the memory at runtime, so there is no need to
> > describe it in DT.
>
> It's probably true, though not providing this controller/device
> separation for NAND controller/devices has proven to be a mistake for
> raw NAND controllers (some props apply to the controllers and others to
> the NAND device, not to mention that some controllers support
> interacting with several chips), so, if that's a new binding, I'd
> recommend having this separation even if it's not strictly required.
>

Note that OneNAND is a totally different thing than the typical NAND
memory with NAND interface. OneNAND chips have a NOR-like interface,
with internal controller and buffers inside, so technically they can
be even used without any special controller on the SoC, via a generic
parallel host interface and possibly some regular DMA engine for CPU
offload.

The controller design of the SoCs in question further abstracts the
OneNAND's programming interface into a number of high level operations
and attempts to hide the details of the underlying memory, so I don't
see the point of describing the memory in DT here, it would actually
defeat the purpose of this controller.

> >
> > > > + - clock: should contain list of phandles and specifiers for all c=
locks listed
> > > > +   in clock-names property.
> > > > + - #address-cells : must be 1,
> > > > + - #size-cells : must be 1.
> > >
> > > This implies some child nodes. What are the child nodes?
> > >
> >
> > I can't recall the reason for this unfortunately.
>
> Defining partitions I guess, but we ask people to use the new
> representation with a 'partitions' sub-node now, so this should
> probably be dropped.

Ah, that could be it indeed. Thanks!

Best regards,
Tomasz