On Thu, Jan 04, 2018 at 09:50:54PM -0600, Kyle Evans wrote: > On Thu, Jan 4, 2018 at 9:14 PM, Frank Rowand <frowand.list@xxxxxxxxx> wrote: > > On 01/04/18 18:39, Kyle Evans wrote: > >> On Thu, Jan 4, 2018 at 7:55 PM, Frank Rowand <frowand.list@xxxxxxxxx> wrote: > >>> On 01/04/18 13:47, Kyle Evans wrote: > >>>> On Thu, Jan 4, 2018 at 3:34 PM, Kyle Evans <kevans@xxxxxxxxxxx> wrote: > >>>>> On Thu, Jan 4, 2018 at 2:41 PM, Kyle Evans <kevans@xxxxxxxxxxx> wrote: > >>>>>> On Thu, Jan 4, 2018 at 2:33 PM, Frank Rowand <frowand.list@xxxxxxxxx> wrote: > >>>>>>> [... snip ...] > >>>>>>> > >>>>>>> Does this remove the need for the proposed patch, or am I still > >>>>>>> missing something? > >>>>>> > >>>>>> ... nope. Apparently I never tested this with this particular dtc(1) > >>>>>> and instead just assumed it did the same as ours- allocate phandle > >>>>>> sparsely, even with -@. That certainly removes the need for this > >>>>>> patch, and I'm somewhat upset that I hadn't previously considered > >>>>>> this. > >>>>>> > >>>>>> @David, Jon: Please disregard all of the patches along these lines... > >>>>>> I'll fix this in our dtc, where it should be fixed. > >>>>>> > >>>>>> Thanks, Frank! > >>>>> > >>>>> Actually, I'm kind of torn on whether this is useful or not. With > >>>>> being able to have EFI-provided FDT, it's hard to guarantee whether > >>>>> the FDT we're provided has been compiled with GPL dtc(1) and -@. The > >>>>> above solves this problem for most of my personal use-cases , though, > >>>>> since I can guarantee that our FDT and U-Boot provided FDT is compiled > >>>>> properly. > >>>> > >>>> Apologies for the triple post; I realized that this argument is > >>>> inherently wrong, since we can't reference the node if there's no > >>>> symbol anyways. > >>>> > >>>> The only way this might still be a good idea is to support more > >>>> minimal cases where an implementation might prefer to not create a > >>>> phandle for nodes that haven't been referenced. > >>>> > >>>> In our case, we have a function [1] that walks the tree and generates > >>>> metadata on nodes that have phandles, under the assumption that these > >>>> have been referenced somewhere and provides a way to more quickly > >>>> reference these specifically through a separate linked link. > >>>> Allocating phandles for everything as GPL dtc does adds quite a bit > >>>> more overhead to this. > >>>> > >>>> [1] http://src.illumos.org/source/xref/freebsd-head/sys/dev/ofw/openfirm.c#119 > >>> > >>> The "-@" option does not add a phandle to _every_ node, just to nodes > >>> that have a label: > >>> > >> > >> In practice, this is still a not necessarily close superset of those > >> that are actually going to actually get referenced in a given .dts. I > >> note that a number of nodes will still get labelled that are unlikely > >> to be referenced for any number of reasons. > >> > >> For instance, as an example [1][2][3] of one of the boards I'm working > >> on currently, all of the ehci/ohci/mmc nodes, some set of the pio > >> nodes... almost every single node has a label, and most of them don't > >> need a phandle based on what is currently referenced and actually > >> used. I note that 27 of these nodes seem to be referenced, out of 39 > >> nodes with labels (numbers are approximate), leaving ~30% (12) of > >> labelled nodes unreferenced. > >> > >> For a slightly larger example, [4][5][6][7]; 74 referenced nodes out > >> of 113 labelled nodes, leaving ~35% (39) of labelled nodes > >> unreferenced. > >> > >> This is only bothersome because it starts adding up as these things > >> get bigger, and I don't think it really needs to. The alternative to > >> keep phandles down to the minimum set required doesn't add much in > >> maintenance cost or overhead from the overlay application side; > >> especially for blobs generated by this dtc(1) that make the active > >> decision to allocate liberally rather than conservatively. > > > > This concept relies on a hand coded __symbols__ node instead of > > having dtc generate it. This makes the overlay devicetree source > > more fragile. The example dts file in patch 2/2 is fairly safe, > > but it is legal syntax to specify: > > > > test = "/test-node"; > > > > instead of: > > > > test = &test; > > > > And the fragile syntax is exactly what results from a decompiled > > overlay dtb. > > I think I might be misunderstanding something here- our dtc (BSDL > dtc), with -@, still writes a full /__symbols__ node of all labeled > nodes, given that this is what -@ is expected to do. The difference is > that our dtc allocates phandles conservatively because they're a > concept for cross-referencing nodes. Well, kind of. But traditionally *every* node had a phandle (usually it's the actual pointer to the node structure in a live OF). Omitting them is essentially an fdt size optimization. -- 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
Attachment:
signature.asc
Description: PGP signature
