On Wed, Oct 18, 2017 at 11:40 AM, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote: > > (WARNING: sort of newbie alert, but you know that, right? :-) > > was perusing online tutorial on customizing device trees here: > > http://developer.toradex.com/device-tree-customization Never seen that one. > and got a bit confused about the part describing how to (as i read it) > "overwrite" entire nodes. > > first, part on "overwriting properties" makes perfect sense -- > here's an example in that piece about overwriting default USB mode: > > &usb0 { > dr_mode = "host"; > }; > > so, as i've always understood it, the above will do one of two things: > > 1) if that property is not set in the node referenced by that label, > it will be *added* to what is already there, or > > 2) if that property is already set (to whatever), it will be > overwritten > > so far, so good? Yes. > as a special example of that right below that, there's a short > paragraph called "Activating/Deactivating Devices" that uses this > example: > > &uart4 { > status = "okay"; > }; > > but, really, that's just a special case of the first example so > there's nothing new here. but it's the next section called > "Overwriting nodes" that seems confusing: > > "Whole nodes can be overwritten by simply redefining them. Like > overwriting properties, latter definitions overwrite earlier > definitions." I don't think that's right. I think you have to use /delete-node/ first. > wait, what? entire nodes can be overwritten by redefining them? the > example given looks like this: > > "E.g. to overwrite the pin configuration of Vybrids UART2 (UART_B) > overwrite the uart2grp node by simply redefining it in your device > tree ..." > > with the device tree content > > &iomuxc { > vf610-colibri { > pinctrl_uart2: uart2grp { > fsl,pins = < > VF610_PAD_PTD0__UART2_TX 0x21a2 > VF610_PAD_PTD1__UART2_RX 0x21a1 > >; > }; > ... > }; > }; > > hang on ... isn't "vf610-colibri" also a "node" in this device tree? > does the above mean that the *entire* vf610-colibri node is being > overwritten? and that i would have to supply the entire new content of > that node, including simply duplicating the rest of the content that > is already there that i want to keep? (is that what the "..." > represents?) No, you should get a merged vf610-colibri node with the original contents and any new or overwritten properties from this chunk. IOW, only properties are overwritten. > that seems bizarre, but it's what that wording seems to suggest. can > someone clarify what would happen in the above, and give perhaps a > link to the part of the DTspec that covers this? i'm sure i must be > misreading this. It's all source syntax which is mostly outside the scope of the spec. Rob -- 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
