Re: [PATCH v8 1/4] dt-bindings: clock: Document external clocks for MSM8998 gcc
From: Jeffrey Hugo
Date: Tue Nov 12 2019 - 17:03:35 EST
On 11/12/2019 2:18 PM, Rob Herring wrote:
On Tue, Nov 12, 2019 at 1:38 PM Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx> wrote:
On 11/12/2019 11:37 AM, Rob Herring wrote:
On Tue, Nov 12, 2019 at 10:25 AM Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx> wrote:
On 11/11/2019 5:44 PM, Rob Herring wrote:
On Fri, Nov 08, 2019 at 04:17:16PM -0700, Jeffrey Hugo wrote:
The global clock controller on MSM8998 can consume a number of external
clocks. Document them.
Signed-off-by: Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx>
---
.../devicetree/bindings/clock/qcom,gcc.yaml | 47 +++++++++++++++-------
1 file changed, 33 insertions(+), 14 deletions(-)
diff --git a/Documentation/devicetree/bindings/clock/qcom,gcc.yaml b/Documentation/devicetree/bindings/clock/qcom,gcc.yaml
index e73a56f..2f3512b 100644
--- a/Documentation/devicetree/bindings/clock/qcom,gcc.yaml
+++ b/Documentation/devicetree/bindings/clock/qcom,gcc.yaml
@@ -40,20 +40,38 @@ properties:
- qcom,gcc-sm8150
clocks:
- minItems: 1
1 or 2 clocks are no longer allowed?
Correct.
The primary reason is that Stephen indicated in previous discussions
that if the hardware exists, it should be indicated in DT, regardless if
the driver uses it. In the 7180 and 8150 case, the hardware exists, so
these should not be optional.
Agreed. The commit message should mention this though.
Fair enough, will do.
The secondary reason is I found that the schema was broken anyways. In
the way it was written, if you implemented sleep, you could not skip
xo_ao, however there is a dts that did exactly that.
If a dts can be updated in a compatible way, we should do that rather
than carry inconsistencies into the schema.
The third reason was that I couldn't find a way to write valid yaml to
preserve the original meaning. when you have an "items" as a subnode of
"oneOf", you no longer have control over the minItems/maxItems, so all 3
became required anyways.
That would be a bug. You're saying something like this doesn't work?:
oneOf:
- minItems: 1
maxItems: 3
items:
- const: a
- const: b
- const: c
Yes. That specifically won't work. "items" would need to have the dash
preceding it, otherwise it won't compile if you have more than one. But
ignoring that, yes, when it compiled, and I saw the output from the
check failing (after adding verbose mode), min and max for the items
list would be 3, and the check would fail.
A '-' before items would make oneOf have 2 separate schemas. That
would pass with any values for 1-3 items except it would fail for 3
items with [a, b, c] because 2 oneOf clauses pass.
What I was trying to do was something like:
oneOf:
-minItems: 1
-maxItems: 3
-items:
-const: a
-const: b
-const: c
-items:
-const: x
-const: y
-const: z
Where you have to have either [x, y, z] xor a set from [a, b, c]. One
of the two items lists, where min/max is applied to the first one. "-"
on both of the items is needed since you can't seem to have the same tag
more than one at the same scope level.
Probably this was a flawed idea from the start.
I find it disappointing that the "version" of
Yaml used for DT bindings is not documented,
Not sure which part you mean? json-schema is the vocabulary which has
a spec. The meta-schema then constrains what the json-schema structure
should look like. That's still evolving a bit as I try to improve it
based on mistakes people make. Then there's the intermediate .dt.yaml
format used internally. That's supposed to stay internal and may go
away when/if we integrate the validation into dtc.
So, this is probably off-topic, but hopefully you'll find this useful.
I'm interested in knowing the pain points.
I'm probably in the minority, but I really haven't used json-schema nor
yaml before. I have experience with other "schema" languages, so I
figured I could pick what I need from the documentation.
Well, json-schema was new to me before this. There's definitely some
things I really don't love about it, but it's better than trying to
define our own language. It's generally been able to handle some of
the more complex cases.
The only documentation I see is writing-schema.md and example-schema.yaml
To me, writing-schema.md is insufficient. Its better than nothing, so
I'm still glad it exists, but I don't have any confidence I can really
write a binding yaml from scratch based on it. It does a good thing by
telling you what are important properties of a binding, so based on that
you can kind of start to understand how existing bindings actually work.
Its great in telling you how to run the validation checks (the Running
checks) section. The dependencies section is awesome from my
perspective - most projects seem to assume you just know what their
dependencies are, and its painful to try to figure them out when you get
cryptic errors during make.
Where it really fails is that I get no sense of the language. As a
minimum a lexigraphic specification that would allow me to write a
compiler (I've done this before). Then I would understand what are the
keywords, and where they are valid. I wouldn't understand what they
mean, but at-least I can look at some implemented examples and
extrapolate from there.
Have you by chance ever looked at the ACPI spec? Maybe not the best
example, but its the one that comes to my mind first. ACPI has ACPI
Source Language (ASL). Its an interpreted hardware description language
that doesn't match yaml, but I think the ACPI spec does a reasonable job
of describing it. You have a lexographic definition which seems to be
really helpful to ACPICA in implementing the intrepreter. It lists all
of the valid operators, types, etc. It provides detailed references of
each keyword - how they are used, what they do, etc. Its not the
greatest at "how to write ASL 101" or "these are common problems that
people face, and how they can be solved", but atleast with what there
is, I could read every keyword that seems to be possibly related to what
I want to do, and hazard a guess if it would work for my problem.
I have not read the ACPI spec.
Perhaps that is outside the scope of the writing-schema.md document,
that is fair. However, I argue that the document does not provide
sufficient references. The document provides a reference to the
json-schema spec, but the spec is kinda useless (atleast I feel that it
is). "minItems" is not defined anywhere in the spec. What does it
mean? How can I use it? Specific to minItems/maxItems, I'll I've
gathered about it is from example-schema.yaml which indicates its a way
to identify mandatory and optional values for a property, but it doesn't
describe the fact that order matters, and you cannot mix/match things -
IE it looks like you need atleast min items, and at most max items, but
even if you have enough items to satisfy min, there cannot be gaps (you
can't pick items 1, 5, 10 from the list). I only found that out from
running the validation checks with trial/error.
I think you looked at the 'Core' spec rather than the 'Validation' spec:
http://json-schema.org/draft/2019-09/json-schema-validation.html
Though that has moved on to a newer version and we're still on draft7
which is here:
https://tools.ietf.org/html/draft-handrews-json-schema-validation-01
Yes, that looks completely different than what I read. Thanks for the
direct link. I'm going to go read it.
I guess a direct link to this with 'Details on json-schema keywords is
here' would be helpful.
Yes please. Or atleast a "Hey, there are actually two specs, 'core' and
'validation'. The 'validation' one is the relevant one. Hopefully that
clarifies any confusion"
minItems/maxItems is the one area we deviate from json-schema
defaults. That's what the 'Property Schema' section calls out.
Order matters for DT too, so that aspect matches up well with
json-schema. That's been a common issue in dts files, so schema
starting to enforce that will be good for new bindings, but somewhat
painful for existing ones.
You are right, order does matter in DT. I think I've gotten used to
just having -names, and assuming if a, b, c, and d are all listed as
optional, that means you could have a and c. However that kind of
breaks the index mapping, so if you have c, you really need a and b as
well. I was attempting to apply that concept to schema, and it wasn't
working. I suspect that concept shouldn't be valid normally.
There is no reference to the yaml spec, despite the document stating
that the bindings are written in yaml.
However, having found the yaml spec, its really not much better than the
json-schema spec, and it doesn't line up because as the document states,
the bindings are not really written in yaml - its a subset of yaml where
a ton of the boilerplate "code" is skipped.
Yeah, there's a lot to YAML that no one uses and I too find the spec
pretty useless (hence why no reference). Like most other uses I've
encountered, we're using a JSON compatible subset which is just lists
and dicts of key/value pairs. The main thing folks need to know and
trip up on are: indentation is important (including no tabs) and pay
attention to '-' or lack of.
What is boilerplate that is skipped? IMO, if you are not strictly
adhering to yaml, then you need to clearly document your own derivative
language so that someone like me whom is being introduced to all of this
for the first time can start to figure out some of it. It would be
helpful to look at other yaml examples, and understand what is
considered to be boilerplate so I can translate that to a DT binding.
We're not skipping any boilerplate. We're not using advanced features
like tags or anchors. You can use any YAML parser including online
ones to read the files.
Ok, so I feel like I've misunderstood this except from writing-schema.md:
"The Devicetree schemas don't exactly match the YAML encoded DT data
produced by dtc. They are simplified to make them more compact and avoid
a bunch of boilerplate."
I thought this meant the bindings were simplified to be more readable,
by skipping boilerplate text. What does it actually mean?
I understand, the majority of the above is complaints and demands which
is really not fair to you, since you are spending what I presume to be
your "non-dayjob" time to make the community better.
It's my day job or part of it, just not enough hours in the day...
However, I don't
really know how to contribute to make the documentation better. I don't
understand enough. As far as this topic is concerned, I'm a dumb monkey
banging on a keyboard hoping to get close enough to Shakespeare to pass
mustard by accident, and maybe learn something along the way so that
next time, I might have an idea of how to do something of what I need.
The challenge is providing enough information to write bindings
without being json-schema experts. My hope is really to build up
enough examples and make the meta-schema good enough to keep folks
within the lines. Maybe that's a flawed approach, but even getting
folks to follow writing-schema.rst and run 'make dt_binding_check' has
been a challenge.
Hopefully you've made it this far - that ended up being a lot more text
that I thought it would be. I really hope this is useful feedback to
you, but let me know if I am still not clear on something. I will try
my best to clarify more. If you feel like I can contribute somehow,
just let me know.
so after several hours of
trial and error, I just gave up since I found this to work (failed cases
just gave me an error with no indication of what was wrong, not even a
line number).
Schema failures or dts failures? It is possible to get line numbers
for either, but that makes validation much slower. In the latter case,
the line numbers aren't too useful either given they are for the
.dt.yaml file and not the .dts source file (dtc integration would
solve that). Adding '-n' to dt-doc-validate or dt-validate will turn
them on though.
Schema compilation failures. I don't recall the exact error message,
but it was something like "no valid schema found, continuing".
Essentially running "dt_binding_check". I tried with -v but wasn't
getting much more in this case. I didn't try -n.
That's before we even validate the schema, so something has gone wrong
pretty early. You may get farther with 'make -k'. I'll have to look
into it. The schemas are actually built twice. They are all built into
processed-schema.yaml. That's supposed to skip any with errors and is
what's used to validate dts files. If that's failing for some reason,
then it's going to be pretty vague. The dt_binding_check rule also
fully validates each binding schema and builds and validates the
examples. It should print more detailed errors (though still sometimes
vague).
Rob
--
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.