# Re: \[RFC/PATCH 2/3\] of: add of\_lookup\_stdout() utility function

- From: Mitch Bradley \<hidden\>
- Date: 2008-08-06 17:09:41 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2008/08/8049083
- Thread: https://ratatoskr.run/linux-devicetree/2008/08/8049081/t.md

```text


Segher Boessenkool wrote:
>> It's not what we do with flattened device trees blobs though.  In the
>> flattened tree we're not using a /chosen/stdout property, just the
>> linux,stdout-path one.
>>
>> The question that remains is; should there be?  Should the dt blobs
>> use /chosen/stdout also?  (I'm not familiar enough with real OF to
>> know the answer.  I'm assuming that an instance value is not the same
>> as a phandle).

The difference between a phandle and an ihandle is similar to the difference between (the inode of) an executable files on disk and (the process id of) a running process.  A phandle refers to the static information that describes a device, while an ihandle refers to a particular (out of potentially several) active instantiation of the OFW driver for that devices.  An "instance value" is a data item that can have a different value for each of the running instances of a given driver.  In the analogy, an instance value is like a data segment variable.

Given an ihandle, you can get the corresponding phandle with ihandle>phandle.  You can't go from phandle to ihandle, because that direction is one-to-many.

Why you you ever need more than one running instance of a given driver?  For leaf devices, it is pretty rare to have multiple instances.  Multiple instances are more often used for intermediate nodes.  The same intermediate node - for example a usb node - is often the parent of several leaf nodes that are active simultaneously.  When you open a device, its device tree parents up to the root are implicitly opened.  Each such instance can hold dynamic state on behalf of its children.

>
> ihandles and phandles are not the same thing in OF.  Since in the
> "flat world" we cannot have instances, we should use phandles instead
> of ihandles for the things in /chosen.  I thought we agreed on that
> already, perhaps I am wrong?
>
>
> Segher
>
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>
```