On Fri, Aug 28, 2015 at 09:26:17AM -0500, Rob Herring wrote: > On Fri, Aug 28, 2015 at 12:23 AM, Matt Porter <mporter@xxxxxxxxxxxx> wrote: > > During the Device Tree microconference at Linux Plumbers 2015, we had > > a short discussion about how to improve DT Binding Documentation. A > > number of issues were raised (again, as these things have been > > discussed in the past) including: > > > > * Inconsistency between binding documents due to prose text > > format. > > * Inability to reliably machine read bindings for mass update > > or search. > > * Bit rot of bindings as new conventions are agreed upon but > > only new bindings are changed. > > Thanks for pulling this together. > > > Grant Likely probably summed up the issue best with "...as long as > > bindings are human readable, we'll have issues...". The context > > of that comment was, of course, regarding our current documents > > written in very inconsistent prose style. When the topic of needing > > the bindings in a rigid format was raised, there was general head > > nodding that this was needed. It was noted that this has been > > discussed many times before and nothing has been done. > > > > My proposed solution to the problem is to convert all DT bindings > > a rigid text markup format. In choosing a text markup language my > > requirements were: > > > > 1) Human readable > > 2) Well documented > > 3) Easy to translate to other data formats > > 4) Well supported by tools and libraries > > > > After looking at a number of markup options, YAML stood out as the > > one that meets all of these requirements. The YAML syntax is adopted > > in many projects specifically because of the high level of readability. > > A comprehensive spec is at http://www.yaml.org/spec/1.2/spec.html. > > There's a number of tools to convert between YAML and other popular > > data formats such as JSON and XML. XML was cited by Behan Webster > > during the microconference as an important data format as the type > > of developers that may produce comprehensive DTS Binding validation > > tools will want to use XML. Every major scripting language has a > > high level binding to the low level libyaml C library to facilitate > > handling of YAML data files. > > Being markup language novice, this looks good to me. > > > One caveat with YAML is it does not tolerate tabs. Yes, I said it. > > No tabs! This can be managed with proper editor modes and also with > > helper scripts to strip tabs to aid in people passing planned > > checkpatch.pl checks that would run YAML DT Binding specific tag > > validators for new bindings. > > What do parsers do with tabs? Throw an error? Yes, they throw an error. Keep in mind that most of what I used to start are general purpose conversion tools on top of a particular scripting languages's high level binding to libyaml. The error output leaves a bit to be desired for our use case. In any case, when I was developing the skeleton.yaml I used the yaml script from https://github.com/ryo/yamltools to catch all these syntax errors I was inserting..like tabs. the PyYaml binding being used in my PoC dtgendoc does the same thing but I don't gracefully handle those errors like we could. > Beyond tabs, how do we check files can be parsed both generically and > for any binding specific requirements. We now need a schema for > checking the schema. We need some equivalent to compile testing. Right. So, I think what you are touching on is something I should have expanded on in the TODO list. Basically, we need a scripted tool that we run from checkpatch.pl that 1) reads the .yaml and validates the YAML itself (that comes for free in the high level parsers) reporting errors in a sensical manner 2) validates our DT binding specific tags Now, I would caution about trying to do too much on Day 1 or we could end up back at the "never doing anything" stage. It would be an improvement to simply check that the basic tags exist as shown in the [R] or [O] fields in the documentation. One thing I should point out is that I carefully avoided marking some tags as [R] where existing bindings don't have them...even if logically, a description should be required on every binding. The idea here is to avoid updating content at the same time that we are updating the format. Rather, I think it would be better to get the base format updated, then come back with a janitorial team and add descriptions (since now we can generate a worklist of those bindings missing a top-level description) and systematically fix those and review with the appropriate maintainers. > An example such as checking that compatible strings are documented as > checkpatch.pl does would be nice. Roughly, that would be just list all > compatible values. Ok, so my comments above were strictly about a validator for the binding doc submission itself. I can add an example based on your checkpatch.pl to adapt it to the .yaml compatible tags. > > The scope of the initial YAML DT Binding format was specifically > > limited to supporting *only* the content we have in bindings today. > > The idea here is to propose and agree on something that will take > > us just a few steps in the right direction. If we move *all* current > > binding content to a machine parseable format, additional features > > can be added with more automation and scripting. As it stands today, > > because of the inconsistency of the wording of the files, we can't > > add a lot of new features to the content until we convert what we > > have today into a standard format. > > > > With that said, it should be noted that some new features such as > > "type" tags to indicate cell types could be added to support > > additional DTS validation beyond what the current content supports. > > Another possibility is adding "range" type information to validate > > the legal values for a cell. > > > > This series is broken up into three major parts: > > > > 1) The documentation defining the YAML DT binding format > > 2) A skeleton device binding example illustrating use of this format > > 3) Some real binding conversions (eeprom.txt, phy-bindings.txt, and > > ti-phy.txt > > > > As a proof of concept of what can be done with a proper machine > > readable DT binding source file, there's a simple markdown document > > generator at https://github.com/konsulko/dtgendoc. Also, to see > > actual output from the generator, the generated markdown from those > > bindings is viewable at https://github.com/konsulko/dtgendoc/wiki > > Nice. > > > There's a lot of other possibilities for validation tools using > > only the data we have today in the bindings. In addition, Frank > > Rowand covered some DT debug techniques that would benefit from > > the binding documentation being 100% reliably searchable. > > > > I found it useful to see a side-by-side view of a converted doc > > versus the original content, so here's a screenshot of eeprom.txt > > vs. eeprom.yaml: > > https://github.com/konsulko/dtgendoc/wiki#eepromtxt-vs-eepromyaml > > > > When we decide on a text markup format that is acceptable, then the > > next step is to convert all the bindings. That process would start > > with the complete set of generic bindings as they will be referenced > > by the actual device bindings. > > You are going to do that for everyone, right? ;) Let's just say that I'm banking on others helping here once we have a format agreed upon. If we can hold the binding doc schema definition initially to just define tags for content that already exists in our textual binding docs, the effort for conversion is tolerable. To give an example, that phy-bindings.txt, it took 15 minutes to convert and and pass through the yaml parser and dtgendoc. The reason is that it's pure reformatting work. It doesn't take any special knowledge of the hardware and it doesn't involve reviewing dts files to extra additional information. Some of the annoyances can be streamlined like tab stripping and handling the two space indentation to make this process faster. One of my next things is to get a simple tool going that reports problems with conversions, essentially what I said was needed to integrate with checkpatch, so this process of conversion is even faster. Trivial peripheral bindings like eeprom.txt can be done in 5 minutes or so right now. If we decide we must have tags like "type:" in the initial binding doc schema definition *and* we must add that content in each conversion, then this becomes more time consuming to validate that information against working dts files. IMHO, we'd be better off to get the base format straight, addressing missing pieces like all the compatible permutations, and convert them all with just that content. After that, we come back and add new content features like type: tagging. I'm trying to find a reasonable place to do this incrementally since the volume of bindings to convert is enormous. But to answer your question, if we get a format I'll do conversions and hope I'm not alone. > I've got some comments on the specific format as well. Great, thanks. -Matt -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
