On Thu, Jul 27, 2017 at 01:58:09PM -0700, Frank Rowand wrote:
> On 07/25/17 00:50, David Gibson wrote:
> > On Mon, Jul 24, 2017 at 10:09:48AM -0700, Frank Rowand wrote:
> >> Hi David,
> >>
> >> (Adding Pantelis and Tom, since I'm going somewhat off-topic from
> >> the original thread, and they are impacted by what I am asking.)
> >>
> >> On 07/15/17 22:35, David Gibson wrote:
> >>> On Thu, Jul 13, 2017 at 09:47:01AM -0700, Florian Fainelli wrote:
> >>>> On 07/12/2017 09:23 PM, Cyril Novikov wrote:
> >>>>> On 7/12/2017 10:10 AM, Florian Fainelli wrote:
> >>>>>> On 07/11/2017 11:15 PM, Cyril Novikov wrote:
> >>>>>>> Hi, all!
> >>>>>>>
> >>
> >> < snip >
> >>
> >>> The
> >>> phandle fixup information goes into the special __local_fixups__ and
> >>> __fixups__ nodes (which have gratuitiously different format, but
> >>> that's a rant for elsewhere).
> >>
> >> < snip >
> >>
> >> And in another email, David describes the __local_fixups__ format
> >> nicely, so I'll just copy that here instead of re-inventing it:
> >>
> >>
> >>> Well, I don't want to invent a new encoding if we can possibly avoid
> >>> it. The current encoding used for overlay generation looks like this
> >>>
> >>> / {
> >>> target: node@0 {
> >>> };
> >>> node@1 {
> >>> ref = <&target>;
> >>> };
> >>> __local_fixups__ = {
> >>> node@1 {
> >>> ref = <0>;
> >>> };
> >>> };
> >>> };
> >>>
> >>> Basically, __local_fixups__ has a subtree which paralells the main
> >>> tree. Each property found under __local_fixups__ is a list of offsets
> >>> at which phandle references appear in the corresponding property in
> >>> the main tree.
> >>
> >> I share your desire to rant about the different formats between
> >> __local_fixups__ and __fixups__. But I have not come up with an
> >> alternate format for __local_fixups__ that makes me happy. The
> >> best format that I have come up with so far would be:
> >
> > Well to fix it minimally, I'd go the other way - make __fixups__ look
> > like __local_fixups__ but augmented with labels. Strings that need
> > parsing aren't a normal thing in the DT.
>
> On the string parsing issue, I agree that string parsing is not normal
> in the DT. If changing format in other ways, I would maybe also change
> the __fixups__ format so that (for an example with two tuples), instead
> of
>
> "A:B:C", "D:E:F"
>
> the format would be
>
> "A", "B", <C>, "D", "E", <F>.
>
> Or a more concrete example, change:
>
> i2c1 = "/fragment@1:target:0";
>
> to
>
> i2c1 = "/fragment@1", "target", <0>;
>
> or (to bikeshed) even change the order to:
>
> i2c1 = <0>, "/fragment@1", "target">;
Right, but by re-using the parallel paths encoding from
__local_fixups__ you can also drop the path element, simplifying this
a bit further.
>
> This may look a little awkward in source form, but in my version
> of what the world should look like, this would not be hand coded
> in a DTS source file, but instead created by dtc in a DTB. Of
> course it could still be viewed as DTS format by de-compiling
> the DTB.
>
> I admit this may be a really bad idea from a human usability
> standpoint, because the source fragment (for example):
>
> __fixups__ {
> i2c1 = <0>, "/fragment@1", "target";
> i2c2 = <8>, "/fragment@1", "target";
> i2c3 = "/fragment@1", "target", <0>;
> i2c4 = "/fragment@1", "target", <8>;
> };
>
> decompiles (via 'dtc -O dts') somewhat cryptically as:
>
> __fixups__ {
> i2c1 = "", "", "", "", "/fragment@1", "target";
> i2c2 = "", "", "", "\b/fragment@1", "target";
> i2c3 = "/fragment@1", "target", "", "", "", "";
> i2c4 = [2f 66 72 61 67 6d 65 6e 74 40 31 00 74 61 72 67 65 74 00 00 00 00 08];
> };
>
>
> -Frank
>
> >
> >> / {
> >> target: node@0 {
> >> };
> >> node@1 {
> >> ref = <&target>;
> >> ref2 = <&target 42 &target_2>;
> >> };
> >> target_2: node@2 {
> >> };
> >> __local_fixups__ = {
> >> x1 = <"node@1/ref" 0>;
> >> x2 = <"node@1/ref2" 0 8>;
> >> };
> >> };
> >> };
> >>
> >> x1 and x2 are abitrary property names.
> >> The format of each __local_fixups__ property is
> >> - path of property referencing a phandle
> >> - list of offsets of the phandle in the property
> >>
> >> As another alternative, Grant was thinking about adding
> >> a new block to the FDT format to contain the phandle
> >> information. That would remove the need to come up
> >> with a convoluted dts syntax, but adds in the problem
> >> of bootloaders corrupting the new block if they were
> >> not aware of it. He had thoughts about versioning
> >> and checksums to detect the corruption it if did
> >> occur.
> >>
> >> If we were starting from scratch, do you have any other
> >> approach that might be fruitful? It seems like maybe
> >> I am missing something that requires thinking outside
> >> the box.
> >
> > I thought about this the other day a bit. If going from scratch, I
> > think the way to do it would be to add a new FDT_REF tag to the
> > structure block stream. After the FDT_PROP tag and its contents,
> > you'd have an arbitrary number of FDT_REF tags, each giving an offset
> > in the preceding property and a label to fix it up to match. Not
> > sure if you'd want separate FDT_REF and FDT_LOCAL_REF or just use an
> > empty label to describe a local ref.
> >
> > This would also allow for extension to say FDT_PATH_REF to insert
> > paths rather than phandles (i.e. a runtime equivalent of prop = &foo;
> > rather than prop = < &foo >;).
> >
> > For encoding the fragments of an overlay, I'd suggest giving them
> > simply as separate subtrees in the structure block, all before the
> > FDT_END tag. At the moment there has to be only a single subtree
> > before the FDT_END, and the top-level FDT_BEGIN is expected to have an
> > empty name. We can extend that to overlays by allowing multiple
> > subtrees, and making the top-level "name" the target label instead.
> >
> > Incidentally, I'd take "label" in all the above to be represented as
> > an old-style OF path. That is, either an absolute path /foo/bar/baz,
> > or a path relative to an alias, alias/foo/bar/baz. That means we can
> > just use the existing defined /aliases, rather than re-inventing it as
> > __symbols__.
> >
>
--
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
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