On Thu, Jul 5, 2018 at 7:18 PM David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > > On Thu, Jul 05, 2018 at 08:43:49AM -0600, Rob Herring wrote: > > On Wed, Jul 4, 2018 at 9:26 PM David Gibson <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > > On Mon, Dec 18, 2017 at 11:20:38AM +0000, Grant Likely wrote: > > > > On Mon, Dec 18, 2017 at 4:34 AM, David Gibson > > > > <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > > > On Tue, Dec 12, 2017 at 12:48:10PM +0000, Grant Likely wrote: > > > > >> On Tue, Dec 12, 2017 at 6:14 AM, David Gibson > > > > >> <david@xxxxxxxxxxxxxxxxxxxxx> wrote: > > > > >> > On Tue, Nov 28, 2017 at 11:57:09AM +0000, Grant Likely wrote: > > > > >> >> The current code throws away all the data type and grouping information > > > > >> >> when parsing the DTS source file, which makes it difficult to > > > > >> >> reconstruct the data format when emitting a format that can express data > > > > >> >> types (ie. dts and yaml). Use the marker list to mark the beginning and > > > > >> >> end of each integer array block (<> and []), the datatype contained in > > > > >> >> each (8, 16, 32 & 64 bit widths), and the start of each string. > > > > >> >> > > > > >> >> At the same time, factor out the heuristic code used to guess a property > > > > >> >> type at emit time. It is a pretty well defined standalone block that > > > > >> >> could be used elsewhere, for instance, when emitting YAML source. Factor > > > > >> >> it out into a separate function so that it can be reused, and also to > > > > >> >> simplify the write_propval() function. > > > > >> >> > > > > >> >> When emitting, group integer output back into the same groups as the > > > > >> >> original source and use the REF_PATH and REF_PHANDLE markers to emit the > > > > >> >> the node reference instead of a raw path or phandle. > > > > >> >> > > > > >> >> Signed-off-by: Grant Likely <grant.likely@xxxxxxx> > > > > >> > > > > > >> > I'm a bit dubious how well forcing the marker mechanism to do all this > > > > >> > stuff it was never intended for can work in the long term. Still, > > > > >> > it's an interesting experiment. > > > > >> > > > > >> As long as the actual data is stored as flat buffer, the markers > > > > >> mechanism works quite well for this. I tried doing something entirely > > > > >> separate, and it turned out to be awful. Another alternative is to > > > > >> break up the flat buffer into a chain of data blocks with attached > > > > >> type information, but that is a very invasive change. > > > > >> > > > > >> This approach has the advantage of being robust on accepting both > > > > >> typed and anonymous data. If the markers are not there then the > > > > >> existing behaviour can be maintained, but otherwise it can emit a > > > > >> higher fidelity of source language. > > > > > > > > > > Hm, true. The approach is growing on me. I guess what I'm still > > > > > dubious about is how much this type annotation can get us to approach > > > > > the YAML model. For example, YAML can distinguish between [ [1, 2], > > > > > [3, 4] ] and [1, 2, 3, 4] which isn't really feasible in dtc. > > > > > > > > To start with I'm constraining what is permissible in the YAML > > > > encoding. So, even though YAML can encode multiple nested lists, I'm > > > > not permitting that in this iteration. To take an example: > > > > > > > > in dts: reg = <0x1000 0x100> <0x4000 0x300>; > > > > In YAML I'm encoding as: reg: [ [0x1000, 0x100], [0x4000, 0x300] ] > > > > > > > > in dts: compatible = "acme,uart9000", "ns16550" > > > > is in YAML: compatible: [ "acme,uart9000", "ns16550"] > > > > > > > > in dts: #size-cells = <1>; > > > > in YAML: "#size-cells": [ [ 1 ] ] > > > > > > > > in dts: uint16-prop = /bits/ 16 <31>; > > > > in YAML: uint16-prop: [ !uint16 [31] ] > > > > > > > > I'm not allowing anything outside that pattern. So, the following are > > > > all disallowed currently: > > > > reg: [0x1000, 0x100, 0x4000, 0x300] /* integers need to be in a list - > > > > maps to <...> in dts */ > > > > compatible: "ns16550" /* not encoded into list */ > > > > reg: [ [ [0x4, 0xffff0000], 0x80000], [ [0x4, 0xfffe0000], 0x40000] ] > > > > /* Triple nesting not allowed*/ > > > > > > Sorry, I meant to make a comment on this months ago, but never got > > > around to it. In terms of the immediate problem here, this seems like > > > a reasonable approach. However, it kind of underscores the lingering > > > worries I have about using YAML as a DT encoding format. In the > > > JSON/YAML world, 1 and [ [ 1 ] ] are different things, and using the > > > later as a way of encoding what's essentially a plain integer would be > > > pretty perverse. > > > > For the schema, I've taken the approach of converting single values to > > arrays/matrices within the validation tools. Otherwise, we end up with > > a lot of boilerplate in schema docs. > > Right, I'm not surprised you needed that. > > > > So, I'm concerned that if we have YAML front-and-centre to the user, > > > it will be pretty misleading as to what is and isn't possible. > > > > I would like to make the YAML encoding just an intermediate format to > > use for validation purposes. > > Yeah, I think that's a safer approach. > > > This would give us some flexibility > > versus having a fixed format that's set in stone. And we wouldn't need > > to figure out support such as includes, /directives/, etc. or support > > YAML input. So how do we support YAML in dtc and not make it > > front-and-centre? > > Right, which I think amounts to not encouraging its use as an actual > source format. Lack of input support in dtc will do that. I'm using it as a source format currently for test cases, but those could easily be converted to dts. > A few things to consider: > * Maybe use plain JSON instead of YAML as our intermediate > validation format - it's intended more for machines than humans It's an easy switch on the validation side since the python representations are the same. It will be more work switching dtc as C libraries don't have a common representation. If the output was completely hidden, then it really wouldn't matter. But for debugging purposes, a human may be looking at the output, so I think it would be better to use YAML everywhere than a mixture. It's not exactly hard to understand JSON, but it is potentially one more thing for people. I've thought some about using JSON already because I also output the processed schema docs to speed up the validation. I thought using JSON may have been a little faster, but I did some tests and didn't find any significant difference. > * Don't put much effort into pretty printing the JSON / YAML, as > long as it's parseable by the validation chain JSON can't have comments. So we wouldn't be able to add source annotations. Though, I don't think libyaml gives us a way to add comments anyways. So, I guess we're not putting any effort into prettying printing. Rob -- To unsubscribe from this list: send the line "unsubscribe devicetree-spec" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
