Date:   Tue, 03 Oct 2017 17:13:09 +0300
From:   Pantelis Antoniou <pantelis.antoniou@...sulko.com>
To:     Rob Herring <robherring2@...il.com>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Grant Likely <grant.likely@...retlab.ca>,
        David Gibson <david@...son.dropbear.id.au>,
        Tom Rini <trini@...sulko.com>,
        Franklin S Cooper Jr <fcooper@...com>,
        Matt Porter <mporter@...sulko.com>,
        Simon Glass <sjg@...omium.org>,
        Phil Elwell <philip.j.elwell@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Marek Vasut <marex@...x.de>,
        Devicetree Compiler <devicetree-compiler@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] yamldt v0.5, now a DTS compiler too

Hi Rob,

On Tue, 2017-10-03 at 08:18 -0500, Rob Herring wrote:
> On Mon, Oct 2, 2017 at 2:46 PM, Pantelis Antoniou
> <pantelis.antoniou@...sulko.com> wrote:
> > Hi Rob,
> >
> > On Sun, 2017-10-01 at 17:00 -0500, Rob Herring wrote:
> >> On Thu, Sep 28, 2017 at 2:58 PM, Pantelis Antoniou
> >> <pantelis.antoniou@...sulko.com> wrote:
> >> > Hello again,
> >> >
> >> > Significant progress has been made on yamldt and is now capable of
> >> > not only generating yaml from DTS source but also compiling DTS sources
> >> > and being almost fully compatible with DTC.
> >>
> >> Can you quantify "almost"?
> >>
> >> > Compiling the kernel's DTBs using yamldt is as simple as using a
> >> > DTC=yamldt.
> >>
> >> Good.
> >>
> >> >
> >> > Error reporting is accurate and validation against a YAML based schema
> >> > works as well. In a short while I will begin posting patches with
> >> > fixes on bindings and DTS files in the kernel.
> >>
> >> What I would like to see is the schema format posted for review.
> >>
> >
> > I'm including the skeleton.yaml binding which is the template for
> > the bindings and a board-example.yaml binding for a top level binding.
> >
> >> I would also like to see the bindings for top-level compatible strings
> >> (aka boards) as an example. That's something that's simple enough that
> >> I'd think we could agree on a format and start moving towards defining
> >> board bindings that way.
> >>
> >
> > Note there is some line wrapping I'm including a link
> > to the github repo of the files:
> >
> >
> > The skeleton.yaml
> >
> > https://raw.githubusercontent.com/pantoniou/yamldt/master/validate/bindings/skeleton.yaml
> >
> > %YAML 1.1
> > ---
> > # The name of the binding is first
> > # The anchor is put there for use by others
> > skeleton: &skeleton
> 
> This and "id" seem redundant.
> 

Indeed.

> >   version: 1
> >
> >   id: skel-device
> >
> >   title: >
> >     Skeleton Device
> >
> >   maintainer:
> >     name: Skeleton Person <skel@...nel.org>
> >
> >   description: >
> >     The Skeleton Device binding represents the SK11 device produced by
> >     the Skeleton Corporation. The binding can also support compatible
> >     clones made by second source vendors.
> >
> >   # The class is an optional property that declares this
> >   # binding as part of a larger set
> >   # Multiple definitions are possible
> >   class: [ device, spi-device ]
> >
> >   # This binding inherits property characteristics from the generic
> >   # spi-slave binding
> >   # Note that the notation is standard yaml reference
> >   inherits: *spi-slave
> >
> >   # virtual bindings do not generate checkers
> >   virtual: true
> 
> virtual is an overloaded term.
> 

OK, what term should I use that this binding should not be instantiated
as a checker, only be used by other bindings when inherited?

> >
> >   # each property is defined by each name
> >   properties:
> >
> >     # The compatible property is a reserved name. The type is always
> > "string"
> >     # and should not be repeated device binding.
> >     compatible:
> >       category: required        # required property
> >       type: strseq              # is a sequence of strings
> >
> >       description: >
> >         FX11 is a clone of the original SK11 device
> >
> >       # v is always the name of the value of the property
> >       # np is passed to the checker and is the current
> >       # node pointer. We can access properties and call
> >       # methods that operate on them.
> >       # There can be multiple constraints, just put them
> >       # into a sequence.
> >       # Note that the BASE("skel,sk11") form from the previous
> >       # binding will have to be reworked.
> >       constraint: |
> >         anystreq(v, "skel,sk11") ||
> >         anystreq(v, "faux,fx11")
> 
> Constraints and logic ops were certainly not decided in the last
> attempt and I think will be the hardest part to define. I see you are
> using eBPF in the checker. Is that where anystreq comes from?
> 

Yes. The ebpf environment declares a number of methods that are executed
outside the ebpf sandbox. Check out

https://raw.githubusercontent.com/pantoniou/yamldt/master/validate/schema/codegen.yaml
https://github.com/pantoniou/yamldt/blob/master/ebpf_dt.c

> How would you express the ordering requirement (most significant
> compatible first)?
> 

Err, there might be new bpf API needed there. For the first stab at
the bindings problem I concentrated on getting things working and be as
clear as possible.

You could do something like that:

   orderedstrseq(v, (const char *[]){ "skel,sk11", "faux,fx11", NULL })

Which would check ordering too.

Obviously you'd hide the weird syntax using a macro.

#define ORDEREDSTRSEQ(_v, ...) \
	orderedstrseq(_v, (const char *[]){ __VA_ARGS__ , NULL })


So you'd write the above as:

	ORDEREDSTRSEQ(v, "skel,sk11", "faux,fx11")

> >
> >     # The reg property is a reserved name. The type is always "int" and
> >     # should not be repeated in a device binding. Constraints are
> > defined
> >     # only in the context of the parent node's address, size, and ranges
> >     # cells. The description is inherited from the spi-slave binding.
> >     # Note that if inheriting from a base binding this declaration may
> >     # be omitted.
> >     reg:
> >       category: required        # required property
> >       type: intseq              # is a sequence of integers
> >
> >     # spi-max-frequency needs the device-specific constraint to be
> > supplied
> >     spi-max-frequency:
> >       # this constraint is dependent on the compatible property
> >       # property containing "skel,sk11"
> >       constraint: |
> >         v <= anystreq(get_strseq(np, "compatible"), "skel,sk11") ?
> > 10000000 : 1000000
> >
> >     # This property overrides the generic binding description with
> >     # a device specific description in order to mention the chip's
> >     # h/w cfg strapping pins.
> >     spi-cs-high:
> >       description: >
> >         Set if skeleton device configuration pins are set for chip
> >         select polarity high
> >
> >     # Device specific properties don't inherit characteristic from a
> > generic
> >     # binding so category, type, constraint, and description must be
> > specified
> >     # if needed.
> >     skel,deprecated1:
> >       # note that the category may be declare more than one option
> >       category: [ deprecated, optional ]
> >       type: int
> >       constraint: |
> >         v >= 100000 && v <= 200000
> >       description: >
> >         First of two deprecated properties.
> >
> >     # There are no constraints for properties of empty type
> >     skel,deprecated2:
> >       category: deprecated
> >       type: empty
> >       description: >
> >         Second of two deprecated properties.
> >
> >     # This example could be auto-generated rather than explicitly
> > included
> >     # in the yaml source.
> >     # Note that the YAML example must be validated against this binding
> >     # to be an accepted entry
> >     example:
> >
> >       dts: |
> >         sk11@0 {
> >             compatible = "skel,sk11";
> >             reg = <0>;
> >             spi-max-frequency = <1000000>;
> >             spi-cs-high;
> >         };
> >
> >       yaml: |
> >         sk11@0:
> >           compatible: "skel,sk11"
> >           reg: 0
> >           sip-max-frequency: 1000000
> >           spi-cs-high: true
> >         ---
> > ...
> >
> > And board-example.yaml
> >
> > https://raw.githubusercontent.com/pantoniou/yamldt/master/validate/bindings/board-example.yaml
> >
> > %YAML 1.1
> > ---
> > board-example: &board-example
> >   version: 1
> >
> >   title: A board example using compatible and model properties
> >
> >   maintainer:
> >     name: Skeleton Person <skel@...nel.org>
> >
> >   class: board
> >
> >   # this binding is selected when the compatible property constraint
> > matches
> >   selected: "compatible"
> 
> We need some way to express this must be the root node. More
> generally, we need to express what bindings must be a child of (think
> sub-devices in MFDs). Perhaps that's just a "parent" key with the
> value being the id/name.

> >
> >   description: >
> >     A board binding example. Matches on a top-level compatible string
> > and model.
> >
> >   properties:
> >
> >     compatible:
> >       category: required
> >       type: strseq
> >       description: |
> >         Compatible strings for the board example.
> >         The depth of the node must be zero, i.e. root.
> >
> >       constraint: |
> >         get_depth(np) == 0 && (
> 
> Ahh, I guess this is how you are doing it. I don't think this works
> for any value other than 0. An MFD could be at any level.
> 

Well, I could've used a streq(get_name(get_parent(np)), "/") test but
this is faster. It's up to you what would work best.

> >         anystreq(v, "example,evm") ||
> >         anystreq(v, "example,evm2") ||
> >         anystreq(v, "example,base"))
> >
> >     model:
> >       category: required
> >       type: str
> >       description: models that this board family supports
> >       constraint: |
> >         streq(v, "Example EVM") ||
> >         streq(v, "Example EVM2")
> >
> >   example:
> >     dts: |
> >       / {
> >           compatible = "example,evm", "example,base";
> >           model = "Example EVM";
> >       };
> >     yaml: |
> >       compatible: [ "example,evm", "example,base" ] ;
> >       model: "Example EVM";
> 
> I really don't want to see 2 examples. For now, it's going to be dts
> format. It could be converted by script later if needed.
> 
> Overall, I think this format is a bit long for boards. We have
> something like ~1000 boards in arch/arm last I checked. I want adding
> a board binding to be very short and easy to review. It's often only a
> 1 line change. The main issue I have is it is just each SoC (or SoC
> family) does things their own way.
> 

Well, this is a full featured example; you could declare this a
'virtual' (or what ever you want to call it binding) and use:

board-example-foo:

  inherits: *board-example

  properties:
    compatible: ...

It is not absolutely terse, but it's still YAML. But for what is worth,
those YAML files can be generated using the C preprocessor. You could
define a macro that cuts the churn, albeit you lose the ability to
parse them as normal YAML files.

> > As you see it's almost identical to what you've originally posted.
> 
> I barely remember and no one ever commented on it.
> 

I mentioned that before, I wasn't CCed on it :)

> Rob

Regards

-- Pantelis

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