On Mon, Jul 29, 2013 at 10:15:12PM -0400, jonsm...@gmail.com wrote: > On Mon, Jul 29, 2013 at 9:44 PM, David Gibson > <da...@gibson.dropbear.id.au> wrote: > > On Sat, Jul 27, 2013 at 10:11:16PM -0700, James Bottomley wrote: > >> On Sat, 2013-07-27 at 21:28 -0600, Grant Likely wrote: > >> > On Sat, Jul 27, 2013 at 2:25 PM, Grant Likely > >> > <grant.lik...@secretlab.ca> wrote: > >> > > On Sat, Jul 27, 2013 at 2:01 PM, jonsm...@gmail.com > >> > > <jonsm...@gmail.com> wrote: > >> > >> On Sat, Jul 27, 2013 at 3:45 PM, Grant Likely > >> > >> <grant.lik...@secretlab.ca> wrote: > >> > >>> On Sat, Jul 27, 2013 at 4:59 AM, Arend van Spriel > >> > >>> <ar...@broadcom.com> wrote: > >> > >>>> Let's see how many people go and scream if I say this: Too bad .dts > >> > >>>> files > >> > >>>> are not done using XML format as DT bindings could be described > >> > >>>> using XML > >> > >>>> Schema. > >> > >>> > >> > >>> Draft an example and show us how it would look! :-) There is > >> > >>> absolutely nothing preventing us from expressing a DT in XML format, > >> > >>> or even using XSLT to define DT schema while still using our current > >> > >>> .dts syntax. It would be trivial to do lossless translation between > >> > >>> .dts syntax and xml. > >> > >>> > >> > >>> The problem that I have with XML and XSLT is that it is very verbose > >> > >>> and not entirely friendly to mere-mortals. However, I'm more than > >> > >>> willing to be proved wrong on this point. > >> > >> > >> > >> I considered this approach a while ago and discarded it. It would work > >> > >> but it is just too much of a Frankenstein monster. > >> > >> > >> > >> Much cleaner to modify dtc to take a schema as part of the compilation > >> > >> process. The schema language itself has no requirement to look like > >> > >> DTS syntax. Whoever wrote dtc probably has a favorite language that > >> > >> would be good for writing schemas in. > >> > > > >> > > Making it part of dtc is a required feature as far as I'm concerned. > >> > > Using XML/XSLT and dtc-integration are not mutually exclusive, but I > >> > > digress. > >> > > >> > Oops, ignore the XSLT bit. XSLT isn't schema and has no bearing on the > >> > discussion of schema. Sorry for the noise. > >> > >> XSLT is a transform language ... you'd use it say to transform xml to > >> dtc, so it would be an integral component of an xml/xslt based schema. > >> > >> If you want actually to describe and have validated the xml schema > >> itself, then you'd use xsd (XML schema description language) and its > >> associated tools. > >> > >> I'm not saying you *should* do this, just that it's possible (plus I've > >> just blown my kernel cred by knowing about xml, sigh). > > > > Heh. So, it was said in jest, but that actually raises an important > > point. > > > > There are basically two criteria to keep in mind for our > > representation of schemas: > > 1) Adequate expressiveness to validate a sufficiently large part, > > of a sufficiently large number of bindings to be useful. > > 2) Ease of use and ease of learning **for the target audience**. > > > > To the best of my knowledge xsd would do well on (1), but I'm not > > convinced it does very well on (2). In an environment where XML was > > already widely used, XSD would make perfect sense. Here, I think it > > would be pretty ugly to wire onto the existing DT tools and > > infrastructure, and unpleasantly unfamiliar for many kernel and board > > developers trying to work with DT schemas. > > > > > > So, by way of investigation, let me propose an alternative expression > > of schemas, that I'm also not convinced we should do, but is possible > > and expressive. It's illustrative, because it's kind of the polar > > opposite approach to XSD: just use C. > > > > dtc already has a (so far limited) "checks" mechanism which verifies > > various aspects of DT content. These are implemented by C functions > > in checks.c. There's obviously ample expressiveness - you can express > > any constraint you want that way. It can be pretty verbose, and > > fiddly. A good library of helper functions can mitigate that, but > > it's not clear how much. On the other hand, a very good fraction of > > people working with this will already be familiar with C, which is a > > big plus. This is, after all, the reason that the dts syntax is > > chiefly C inspired. > > > > Now, in practice, I think we will want a more convenient schema > > language (just as we wanted dts, rather than manually constructing > > FDTs as C structures). But I absolutely do think, that the schema > > handling should be handled as plugins to the checks mechanism - > > basically we'd have a validate_schemas() check function. > > > > I also think we should consider the option of having a simple and > > straightforward schema language which handles, say, 80% of cases with > > a fall back to C for the 20% of curly cases. That might actually be > > simpler to work with in practice than a schema language which can > > express absolutely anything, at the cost of being awkward for simple > > cases or difficult to get your head around. > > Would C++ work? You can use operating overloading and templates to > change the syntax into something that doesn't even resemble C any > more.
Well, in theory. But given that dtc and the kernel are both in plain
C, I don't think it's a good idea.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
pgpYkcYOfCOCN.pgp
Description: PGP signature
