From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <4899DAD5.9050209@firmworks.com> Date: Wed, 06 Aug 2008 07:09:41 -1000 From: Mitch Bradley MIME-Version: 1.0 To: Segher Boessenkool Subject: Re: [RFC/PATCH 2/3] of: add of_lookup_stdout() utility function References: <20080806055214.30717.86092.stgit@trillian.secretlab.ca> <20080806060239.30717.79273.stgit@trillian.secretlab.ca> <20080805.233205.201125898.davem@davemloft.net> <18585.31504.836857.829592@cargo.ozlabs.ibm.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Cc: linuxppc-dev@ozlabs.org, devicetree-discuss@ozlabs.org, David Miller , miltonm@bga.com List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 > > _______________________________________________ > devicetree-discuss mailing list > devicetree-discuss@ozlabs.org > https://ozlabs.org/mailman/listinfo/devicetree-discuss >