Mixed types of values inside a single property

Mixed types of values inside a single property

[Andy Shevchenko]

Hi, Rob and Krzysztof!

Today on SO one question [1] was popped up, and I, remembering a bit of
the code of device properties in the Linux kernel, was a bit surprised of it
in a way that reading DT specification (0.4-rc1 as of today) doesn't clarify
that either.

Can the specification be a bit more clear about that? Or is it me and the OP of
that question who missed something in the DT spec?

[1]: https://stackoverflow.com/questions/74517569/reading-tuples-in-a-devicetree

-- 
With Best Regards,
Andy Shevchenko

Re: Mixed types of values inside a single property

[Krzysztof Kozlowski]

On 21/11/2022 13:59, Andy Shevchenko wrote:
> 
> Hi, Rob and Krzysztof!
> 
> Today on SO one question [1] was popped up, and I, remembering a bit of
> the code of device properties in the Linux kernel, was a bit surprised of it
> in a way that reading DT specification (0.4-rc1 as of today) doesn't clarify
> that either.
> 
> Can the specification be a bit more clear about that? Or is it me and the OP of
> that question who missed something in the DT spec?
> 
> [1]: https://stackoverflow.com/questions/74517569/reading-tuples-in-a-devicetree

I saw question on Stackoverflow and I saw there answers, but what is the
question to us?

Best regards,
Krzysztof

Re: Mixed types of values inside a single property

[Andy Shevchenko]

On Mon, Nov 21, 2022 at 02:52:37PM +0100, Krzysztof Kozlowski wrote:
> On 21/11/2022 13:59, Andy Shevchenko wrote:
> > 
> > Hi, Rob and Krzysztof!
> > 
> > Today on SO one question [1] was popped up, and I, remembering a bit of
> > the code of device properties in the Linux kernel, was a bit surprised of it
> > in a way that reading DT specification (0.4-rc1 as of today) doesn't clarify
> > that either.
> > 
> > Can the specification be a bit more clear about that? Or is it me and the OP of
> > that question who missed something in the DT spec?
> > 
> > [1]: https://stackoverflow.com/questions/74517569/reading-tuples-in-a-devicetree
> 
> I saw question on Stackoverflow and I saw there answers, but what is the
> question to us?

Does the specification allows mixed types of the values in the same property?
Because reading it doesn't give a hint.

-- 
With Best Regards,
Andy Shevchenko

Re: Mixed types of values inside a single property

[Krzysztof Kozlowski]

On 21/11/2022 15:11, Andy Shevchenko wrote:
> On Mon, Nov 21, 2022 at 02:52:37PM +0100, Krzysztof Kozlowski wrote:
>> On 21/11/2022 13:59, Andy Shevchenko wrote:
>>>
>>> Hi, Rob and Krzysztof!
>>>
>>> Today on SO one question [1] was popped up, and I, remembering a bit of
>>> the code of device properties in the Linux kernel, was a bit surprised of it
>>> in a way that reading DT specification (0.4-rc1 as of today) doesn't clarify
>>> that either.
>>>
>>> Can the specification be a bit more clear about that? Or is it me and the OP of
>>> that question who missed something in the DT spec?
>>>
>>> [1]: https://stackoverflow.com/questions/74517569/reading-tuples-in-a-devicetree
>>
>> I saw question on Stackoverflow and I saw there answers, but what is the
>> question to us?
> 
> Does the specification allows mixed types of the values in the same property?
> Because reading it doesn't give a hint.

I think DT spec allows it ("Format is specific to the property. See the
property definition.") but DT schema mostly not (finite list of property
types). To some level DT schema accepts mixes, e.g. phandle-array
containing phandle and offsets, but that's because phandle is actually
also a number (dtschema/schemas/types.yaml).

Best regards,
Krzysztof

Re: Mixed types of values inside a single property

[Andy Shevchenko]

On Mon, Nov 21, 2022 at 03:23:53PM +0100, Krzysztof Kozlowski wrote:
> On 21/11/2022 15:11, Andy Shevchenko wrote:
> > On Mon, Nov 21, 2022 at 02:52:37PM +0100, Krzysztof Kozlowski wrote:
> >> On 21/11/2022 13:59, Andy Shevchenko wrote:
> >>>
> >>> Hi, Rob and Krzysztof!
> >>>
> >>> Today on SO one question [1] was popped up, and I, remembering a bit of
> >>> the code of device properties in the Linux kernel, was a bit surprised of it
> >>> in a way that reading DT specification (0.4-rc1 as of today) doesn't clarify
> >>> that either.
> >>>
> >>> Can the specification be a bit more clear about that? Or is it me and the OP of
> >>> that question who missed something in the DT spec?
> >>>
> >>> [1]: https://stackoverflow.com/questions/74517569/reading-tuples-in-a-devicetree
> >>
> >> I saw question on Stackoverflow and I saw there answers, but what is the
> >> question to us?
> > 
> > Does the specification allows mixed types of the values in the same property?
> > Because reading it doesn't give a hint.
> 
> I think DT spec allows it ("Format is specific to the property. See the
> property definition.")

And the quoted sentence confuses me. Is it related to _defined_ only properties
(that are in the same document) or is it to any property, then what does the
second part actually mean in the latter case: "see the property definition".
Where?

It might be though it's lack of my understanding the English language
(not a native speaker).

> but DT schema mostly not (finite list of property
> types). To some level DT schema accepts mixes, e.g. phandle-array
> containing phandle and offsets, but that's because phandle is actually
> also a number (dtschema/schemas/types.yaml).

-- 
With Best Regards,
Andy Shevchenko

Re: Mixed types of values inside a single property

[Rob Herring]

On Mon, Nov 21, 2022 at 9:31 AM Andy Shevchenko
<andriy.shevchenko@intel.com> wrote:
>
> On Mon, Nov 21, 2022 at 03:23:53PM +0100, Krzysztof Kozlowski wrote:
> > On 21/11/2022 15:11, Andy Shevchenko wrote:
> > > On Mon, Nov 21, 2022 at 02:52:37PM +0100, Krzysztof Kozlowski wrote:
> > >> On 21/11/2022 13:59, Andy Shevchenko wrote:
> > >>>
> > >>> Hi, Rob and Krzysztof!
> > >>>
> > >>> Today on SO one question [1] was popped up, and I, remembering a bit of
> > >>> the code of device properties in the Linux kernel, was a bit surprised of it
> > >>> in a way that reading DT specification (0.4-rc1 as of today) doesn't clarify
> > >>> that either.
> > >>>
> > >>> Can the specification be a bit more clear about that? Or is it me and the OP of
> > >>> that question who missed something in the DT spec?

Please use devicetree-spec list for questions like this because it's a
spec question and I only see these on my periodic search for non-patch
emails.

> > >>> [1]: https://stackoverflow.com/questions/74517569/reading-tuples-in-a-devicetree
> > >>
> > >> I saw question on Stackoverflow and I saw there answers, but what is the
> > >> question to us?
> > >
> > > Does the specification allows mixed types of the values in the same property?
> > > Because reading it doesn't give a hint.
> >
> > I think DT spec allows it ("Format is specific to the property. See the
> > property definition.")
>
> And the quoted sentence confuses me. Is it related to _defined_ only properties
> (that are in the same document) or is it to any property, then what does the
> second part actually mean in the latter case: "see the property definition".
> Where?

Any property in the schemas. (I would say if not in the spec, but
everything in the spec should have a schema.)

>
> It might be though it's lack of my understanding the English language
> (not a native speaker).
>
> > but DT schema mostly not (finite list of property
> > types). To some level DT schema accepts mixes, e.g. phandle-array
> > containing phandle and offsets, but that's because phandle is actually
> > also a number (dtschema/schemas/types.yaml).

At the spec level, properties are just byte strings. They can be
anything including a file (i.e. FIT images). In theory, you could make
properties C structs if you wanted.

However, since there is 0 type or field size information in the DT
itself, we don't mix data types or sizes. That's enforced at the
schema level and by what APIs we have to read properties.

Rob

Re: Mixed types of values inside a single property

[Andy Shevchenko]

On Tue, Dec 06, 2022 at 09:31:49AM -0600, Rob Herring wrote:
> On Mon, Nov 21, 2022 at 9:31 AM Andy Shevchenko
> <andriy.shevchenko@intel.com> wrote:
> >
> > On Mon, Nov 21, 2022 at 03:23:53PM +0100, Krzysztof Kozlowski wrote:
> > > On 21/11/2022 15:11, Andy Shevchenko wrote:
> > > > On Mon, Nov 21, 2022 at 02:52:37PM +0100, Krzysztof Kozlowski wrote:
> > > >> On 21/11/2022 13:59, Andy Shevchenko wrote:
> > > >>>
> > > >>> Hi, Rob and Krzysztof!
> > > >>>
> > > >>> Today on SO one question [1] was popped up, and I, remembering a bit of
> > > >>> the code of device properties in the Linux kernel, was a bit surprised of it
> > > >>> in a way that reading DT specification (0.4-rc1 as of today) doesn't clarify
> > > >>> that either.
> > > >>>
> > > >>> Can the specification be a bit more clear about that? Or is it me and the OP of
> > > >>> that question who missed something in the DT spec?
> 
> Please use devicetree-spec list for questions like this because it's a
> spec question and I only see these on my periodic search for non-patch
> emails.

Sure. I will try to not forget this next time I will have a question against DT
spec (I don't expect this will be anytime soon, though).

> > > >>> [1]: https://stackoverflow.com/questions/74517569/reading-tuples-in-a-devicetree
> > > >>
> > > >> I saw question on Stackoverflow and I saw there answers, but what is the
> > > >> question to us?
> > > >
> > > > Does the specification allows mixed types of the values in the same property?
> > > > Because reading it doesn't give a hint.
> > >
> > > I think DT spec allows it ("Format is specific to the property. See the
> > > property definition.")
> >
> > And the quoted sentence confuses me. Is it related to _defined_ only properties
> > (that are in the same document) or is it to any property, then what does the
> > second part actually mean in the latter case: "see the property definition".
> > Where?
> 
> Any property in the schemas. (I would say if not in the spec, but
> everything in the spec should have a schema.)

Maybe we should add these words explicitly there?

> > It might be though it's lack of my understanding the English language
> > (not a native speaker).
> >
> > > but DT schema mostly not (finite list of property
> > > types). To some level DT schema accepts mixes, e.g. phandle-array
> > > containing phandle and offsets, but that's because phandle is actually
> > > also a number (dtschema/schemas/types.yaml).
> 
> At the spec level, properties are just byte strings. They can be
> anything including a file (i.e. FIT images). In theory, you could make
> properties C structs if you wanted.
> 
> However, since there is 0 type or field size information in the DT
> itself, we don't mix data types or sizes. That's enforced at the
> schema level and by what APIs we have to read properties.

Thanks for clarification!

-- 
With Best Regards,
Andy Shevchenko