Hi Philipp, On Friday 14 March 2014 13:19:39 Philipp Zabel wrote: > Am Donnerstag, den 13.03.2014, 18:13 +0100 schrieb Laurent Pinchart: > > On Thursday 13 March 2014 12:08:16 Philipp Zabel wrote: > > > Am Montag, den 10.03.2014, 14:37 +0000 schrieb Grant Likely: > > > > > > Nak. I made comments that haven't been resolved yet. I've replied > > > > > > with more detail tonight. The big issues are how drivers handle > > > > > > the optional 'ports' node and I do not agree to the double-linkage > > > > > > in the binding description. > > > > > > so as I understand it, nobody is against dropping the double-linkage > > > *if* we can agree on a way to recreate the backlinks in the kernel. > > > > I'm not sure about "nobody", but even though it might not be my favorite > > option I'd be OK with that. > > Ok, I make that assumption going by the discussion about link direction that > ensued. > > > > My current suggestion would be to parse the complete device tree into an > > > internal graph structure once, at boot to achieve this. This code could > > > look for the optional 'ports' node if and only if the parent device node > > > contains #address-cells != <1> or #size-cells != <0> properties. > > > > With backlinks in DT we can assume that, if a node is the target of a > > link, it will be compatible with the of-graph bindings, and thus parse > > the node to locate other ports and other links. This allows parsing the > > full graph without help of individual drivers. > > Yes. > > > Without backlinks in DT we need to parse the full DT to reconstruct > > backlinks in the kernel. One possible issue with that is that we can't > > know whether a node implements the of-graph bindings. We can use the > > heuristic you've described above, but I wonder if it could lead to > > problems. Grant pointed out that the compatibility string defines what > > binding a node uses, and that we can't thus look for properties randomly. > > I don't think there's a risk to interpret an unrelated node as part of a > > graph though. > > False positives would just take up a bit of space in the endpoint lists, but > otherwise should be no problem, as they would only be used when either a > driver implementing the bindings is bound, or when they are connected to > other endpoints. Whether or not we scan the whole tree, using this > heuristic, is more a matter of principle. That is my understanding as well, so we should be good there. > > > People completely disagree about the direction the phandle links should > > > point in. I am still of the opinion that the generic binding should > > > describe just the topology, that the endpoint links in the kernel > > > should represent an undirected graph and the direction of links should > > > not matter at all for the generic graph bindings. > > > > I would also not mandate a specific direction at the of-graph level and > > leave it to subsystems (or possibly drivers) to specify the direction. > > Thank you. Can everybody live with this? -- Regards, Laurent Pinchart -- 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
