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

[Boris Brezillon <boris.brezillon@bootlin.com>]

On Wed, 06 Jun 2018 14:14:23 +0200
Stefan Agner <stefan@agner.ch> wrote:

> On 06.06.2018 13:07, Thierry Reding wrote:
> > 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".  
> 
> The reference manual states:
> "16.0 NAND FLASH CONTROLLER
> 
> The NAND flash controller allows Tegra 2 Processor to access NAND flash
> memories for mass storage."
> 
> So I guess "nvidia,tegra20-nand-flash-controller" would be most
> explicit. But the manual also has "GPIO controller" and we use
> "nvidia,tegra20-gpio" as compatible string.
> 
> I dislike nfc since it is an increasingly less known abbreviation and
> not used in the reference manual at all.
> 
> "nvidia,tegra20-nand" or "nvidia,tegra20-nand-flash-controller" is fine
> for me...

Enough bikeshedding, let's go for "nvidia,tegra20-nand" :-). As long as
the representation clearly differentiate the NAND controller and the
NAND chips I'm fine with it.