linux-kernel - Re: [PATCH v3 3/6] mtd: rawnand: tegra: add devicetree binding

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Date:   Wed, 6 Jun 2018 12:45:40 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Dmitry Osipenko <digetx@...il.com>, Stefan Agner <stefan@...er.ch>,
        dwmw2@...radead.org, computersforpeace@...il.com,
        marek.vasut@...il.com, robh+dt@...nel.org, mark.rutland@....com,
        benjamin.lindqvist@...ian.se, pgaikwad@...dia.com, dev@...xeye.de,
        mirza.krak@...il.com, richard@....at, pdeschrijver@...dia.com,
        linux-kernel@...r.kernel.org, krzk@...nel.org,
        jonathanh@...dia.com, devicetree@...r.kernel.org,
        linux-mtd@...ts.infradead.org, marcel@...wiler.com,
        miquel.raynal@...tlin.com, linux-tegra@...r.kernel.org
Subject: Re: [PATCH v3 3/6] mtd: rawnand: tegra: add devicetree binding

Hi Thierry,

On Wed, 6 Jun 2018 12:39:03 +0200
Thierry Reding <thierry.reding@...il.com> wrote:

> On Tue, Jun 05, 2018 at 11:19:14PM +0300, Dmitry Osipenko wrote:
> > On 01.06.2018 10:30, Boris Brezillon wrote:  
> > > On Fri,  1 Jun 2018 00:16:34 +0200
> > > Stefan Agner <stefan@...er.ch> wrote:
> > >   
> > >> This adds the devicetree binding for the Tegra 2 NAND flash
> > >> controller.
> > >>
> > >> Signed-off-by: Lucas Stach <dev@...xeye.de>
> > >> Signed-off-by: Stefan Agner <stefan@...er.ch>
> > >> ---
> > >>  .../bindings/mtd/nvidia-tegra20-nand.txt      | 64 +++++++++++++++++++
> > >>  1 file changed, 64 insertions(+)
> > >>  create mode 100644 Documentation/devicetree/bindings/mtd/nvidia-tegra20-nand.txt
> > >>
> > >> diff --git a/Documentation/devicetree/bindings/mtd/nvidia-tegra20-nand.txt b/Documentation/devicetree/bindings/mtd/nvidia-tegra20-nand.txt
> > >> new file mode 100644
> > >> index 000000000000..5cd984ef046b
> > >> --- /dev/null
> > >> +++ b/Documentation/devicetree/bindings/mtd/nvidia-tegra20-nand.txt
> > >> @@ -0,0 +1,64 @@
> > >> +NVIDIA Tegra NAND Flash controller
> > >> +
> > >> +Required properties:
> > >> +- compatible: Must be one of:
> > >> +  - "nvidia,tegra20-nand"  
> > > 
> > > As discussed previously, I prefer "nvidia,tegra20-nand-controller" or
> > > "nvidia,tegra20-nfc".
> > >   
> > >> +- reg: MMIO address range
> > >> +- interrupts: interrupt output of the NFC controller
> > >> +- clocks: Must contain an entry for each entry in clock-names.
> > >> +  See ../clocks/clock-bindings.txt for details.
> > >> +- clock-names: Must include the following entries:
> > >> +  - nand
> > >> +- resets: Must contain an entry for each entry in reset-names.
> > >> +  See ../reset/reset.txt for details.
> > >> +- reset-names: Must include the following entries:
> > >> +  - nand
> > >> +
> > >> +Optional children nodes:
> > >> +Individual NAND chips are children of the NAND controller node. Currently
> > >> +only one NAND chip supported.
> > >> +
> > >> +Required children node properties:
> > >> +- reg: An integer ranging from 1 to 6 representing the CS line to use.
> > >> +
> > >> +Optional children node properties:
> > >> +- nand-ecc-mode: String, operation mode of the NAND ecc mode. Currently only
> > >> +		 "hw" is supported.
> > >> +- nand-ecc-algo: string, algorithm of NAND ECC.
> > >> +		 Supported values with "hw" ECC mode are: "rs", "bch".
> > >> +- nand-bus-width : See nand.txt
> > >> +- nand-on-flash-bbt: See nand.txt
> > >> +- nand-ecc-strength: integer representing the number of bits to correct
> > >> +		     per ECC step (always 512). Supported strength using HW ECC
> > >> +		     modes are:
> > >> +		     - RS: 4, 6, 8
> > >> +		     - BCH: 4, 8, 14, 16
> > >> +- nand-ecc-maximize: See nand.txt
> > >> +- nand-is-boot-medium: Makes sure only ECC strengths supported by the boot ROM
> > >> +		       are choosen.
> > >> +- wp-gpios: GPIO specifier for the write protect pin.
> > >> +
> > >> +Optional child node of NAND chip nodes:
> > >> +Partitions: see partition.txt
> > >> +
> > >> +  Example:
> > >> +	nand@...08000 {  
> > > 
> > > 	nand-controller@...08000 {
> > >   
> > >> +		compatible = "nvidia,tegra20-nand";  
> > > 
> > > 		compatible = "nvidia,tegra20-nand-controller";
> > > 
> > > or
> > > 
> > > 		compatible = "nvidia,tegra20-nfc";
> > >   
> > 
> > Maybe it's just me, but when I'm reading "nfc", my first association is the
> > "Near Field Communication". Probably an explicit
> > "nvidia,tegra20-nand-controller" variant is more preferable.  

I also prefer nvidia,tegra20-nand-controller.

> 
> We don't really use a -controller suffix for any of the other
> controllers because it is kind of implied. "nfc" is also not something
> that is ever referred to in the technical documentation.
> 
> "nvidia,tegra20-nand" would be most consistent with all the rest of
> Tegra (c.f. "nvidia,tegra*-ahci", "nvidia,tegra*-pci",
> "nvidia,tegra*-hda", "nvidia,tegra*-gmi", ...).

People get confused about what this node represents when you just have
"nvidia,tegra20-nand", and then you start seeing NAND related props or
partition nodes being defined under the NAND controller node.
I really prefer to have the "-controller" prefix here to avoid such
confusions.

Regards,

Boris