On Mon, Jul 17, 2017 at 06:37:47PM -0700, Cyril Novikov wrote: > On 7/15/2017 10:35 PM, David Gibson wrote: > > > But.. I'm very uneasy about the idea. > > > > The first thing, is that this relies on the dts file containing the > > &whatever phandle reference syntax wherever there should be a phandle > > reference. That's normal, but nothing stops a user from simply > > putting an actual number there, manually assigning that number to > > another node's phandle and generating a valid dtb that way. > > > > More importantly, it won't detect phandles if the tree comes from a > > source other than a dts - for example if you flatten /proc/device-tree > > with -I fs, or have code which flattens a tree presented by real Open > > Firmware it won't have that phandle metadata, just integer values. > > Yeah, so the metadata does not contain full information. That's fine because > it's still better than nothing. Hm, ok. > > Now those might not be something that happens in your use case, but > > I'm pretty concerned that if I added this functionality, people are > > going to forget that properties are all, fundamentally, bytestrings > > and get surprised when tools don't magically know where the phandles > > are in some cases. > > > > That said, I'm open to persuasion if a good enough case is made for > > this functionality. > > So, what we need fundamentally is a way to detect dependencies in the > devicetree. Mark is arguing that we cannot *automate* the assignment of > dependent devices to the same VM. However, just detecting that there is a > missing dependency goes a long way. What we have now is guest drivers > failing in various manners, but what they cannot do is point the user to the > specific device that they need, because they don't have the host FDT in > their VM. Makes sense. > For example, a driver may print something like > > [ 2.035071] xuartps ff000000.serial: pclk clock not found. > > To resolve this, the user needs to be proficient with the device tree. Of > course, "pclk" is not a node name in the host FDT. However, if configuration > software could detect this at the time the set of the VM's assigned physical > devices was created, it could give the user the name of the device that > *probably* also needs to be assigned to the same VM. The user wouldn't need > to learn anything about devicetree, they would just need to do a few mouse > clicks to assign the dependent device. And now it's the software's concern > if that assignment is not trivial, as Mark warns us. > > To summarize, full automation is unfeasible and it is understood, but just > the dependency information is very helpful too. Ok, sounds plausible. > > But then, as Mark Rutland says in his other replies, locating phandles > > is far from the only problem in trying to passthrough random DT nodes > > to a guest. > -- 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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