linux-kernel - Re: [RFC 04/11] dt-bindings: Add HTE bindings

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Date:   Sun, 27 Jun 2021 12:56:54 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Dipen Patel <dipenp@...dia.com>
Cc:     "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jon Hunter <jonathanh@...dia.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-tegra <linux-tegra@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Kent Gibson <warthog618@...il.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Linux Doc Mailing List <linux-doc@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>
Subject: Re: [RFC 04/11] dt-bindings: Add HTE bindings

Hi Dipen,

thanks a lot for this very interesting patch set!

I'm gonna try to review properly, just pointing out some conceptual
things to begin with. Bindings is a good place to start.

On Sat, Jun 26, 2021 at 1:48 AM Dipen Patel <dipenp@...dia.com> wrote:

> +description: |
> +  HTE properties should be named "htes". The exact meaning of each htes
> +  property must be documented in the device tree binding for each device.
> +  An optional property "hte-names" may contain a list of strings to label
> +  each of the HTE devices listed in the "htes" property.

I think this is a bit over-abbreviated. IIO has:
io-channels =...
io-channel-names =...

Given DT:s infatuation with using english plural I would opt for:
hardware-timestamps = ..
hardware-timestamp-names = ...

The "engine" part is a bit of an nVidia:ism I think and a too generic
term. Could as well be "processor" or "automata" but nVidia just
happened to name it an engine. (DMA engine would be a precedent
though, so no hard preference from my side.)

When reading this it is pretty intuitively evident what is going on.

Other than that it looks really good!

> +++ b/Documentation/devicetree/bindings/hte/hte.yaml

I would name this hardware-timestamp-common.yamp or so.

> +title: HTE providers

Spell this out: Hardware timestamp providers

> +properties:
> +  $nodename:
> +    pattern: "^hte(@.*|-[0-9a-f])*$"

Likewise:
hardware-timestamp@ ...

I think this is good because it is very unambiguous.

> +examples:
> +  - |
> +    tegra_hte_aon: hte@...0000 {
> +              compatible = "nvidia,tegra194-gte-aon";
> +              reg = <0xc1e0000 0x10000>;
> +              interrupts = <0 13 0x4>;
> +              int-threshold = <1>;
> +              slices = <3>;
> +              #hte-cells = <1>;
> +    };

The examples can be kept to the tegra194 bindings I think, this
generic binding doesn't need an example as such.

> +$id: http://devicetree.org/schemas/hte/nvidia,tegra194-hte.yaml#

This one should be named like this, that is great.

> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Tegra194 on chip generic hardware timestamping engine (HTE)

This is clear and nice.

> +  int-threshold:
> +    description:
> +      HTE device generates its interrupt based on this u32 FIFO threshold
> +      value. The recommended value is 1.
> +    minimum: 1
> +    maximum: 256

Does this mean a single timestamp in the FIFO will generate an IRQ?
Then spell that out so it is clear.

> +  slices:
> +   description:
> +    HTE lines are arranged in 32 bit slice where each bit represents different
> +    line/signal that it can enable/configure for the timestamp. It is u32
> +    property and depends on the HTE instance in the chip.
> +   oneOf:
> +    - items:
> +        - const: 3
> +    - items:
> +        - const: 11

Can't you just use
enum: [3, 11]
?

> +  '#hte-cells':
> +    const: 1

So IMO this would be something like
#hardware-timestamp-cells

Other than this it overall looks very nice to me!

Yours,
Linus Walleij