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

[Thierry Reding <thierry.reding@gmail.com>]

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On Wed, Jun 06, 2018 at 12:45:40PM +0200, Boris Brezillon wrote:
> Hi Thierry,
> 
> On Wed, 6 Jun 2018 12:39:03 +0200
> Thierry Reding <thierry.reding@gmail.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@agner.ch> wrote:
> > > >   
> > > >> This adds the devicetree binding for the Tegra 2 NAND flash
> > > >> controller.
> > > >>
> > > >> Signed-off-by: Lucas Stach <dev@lynxeye.de>
> > > >> Signed-off-by: Stefan Agner <stefan@agner.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@70008000 {  
> > > > 
> > > > 	nand-controller@70008000 {
> > > >   
> > > >> +		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.

Hmm... odd. I mean, the node is already called nand-controller@...,
which makes it pretty obvious to me that this represents a controller
rather than a NAND chip. Also, the placement of this in the DT hierarchy
should make it pretty obvious that it is a controller since you can't
just put a NAND chip directly on the CPU's address bus.

In addition I think the nvidia,tegra* part already pretty strongly
suggests that this is part of an SoC, so further implies "controller".

Thierry

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