On Mon, 2015-05-04 at 19:41 +0300, Pantelis Antoniou wrote: > > You get all of the corner cases handled for free. Perhaps it works for > your case too. > > Perhaps you can educate me on what you need supported and we can make > sure it’s included. Which corner cases ? IE, what I want is simply "update" the device-tree below a PCIe slot on PCI hotplug. The DT isn't "compiled" from a dts (it's amazing how many people seem to believe this is the only way you get fdt's nowadays). It's dynamically (ie programatically) generated by firmware at boot time and contains whatever PCIe devices happen to be plugged during boot. When doing PCIe hotplug operations, the kernel does various FW calls (among others to control slot power), and during these, the FW re-probes underneath the slot and refreshes its internal representation. So the phandles remain fully consistent, there is no fixup needed. We want the kernel to also update his copy as wee in order to avoid keeping stale nodes that don't match what's there anymore. Also, when plugging specific kind of IO drawers, the FW can provide additional node and properties that will be used to control slots inside the drawers. So what we need is: - On PCIe unplug, remove all old nodes below the slot - On PCIe plug, get all the new nodes from FW Note that there is no need to do anything like platform device probing etc... the PCI layer takes care of that, we will remove the old nodes after the pci_dev are gone and create the new ones before Linux re-probes the PCIe bus subtree. So what we need is very simple: The removal can be handled without FW help, and the plug case is a matter of just transferring all those new nodes to Linux to re-expand. Since the phandle etc... are all consistent with the original tree, there is no fixups required. So the "trivial" way to do it (and the way we have implemented the FW side so far) is to have the FW simply "flatten" the subtree below the slot and pass it to Linux, with the intent of expanding it back below the slot node. This is what Gavin proposed patches do. The overlay mechanism adds all sorts of features that we don't seen to need and would make the above more complex. Cheers, Ben. -- 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
