From mboxrd@z Thu Jan 1 00:00:00 1970 From: Srinivas KANDAGATLA Subject: Re: DT: of_platform_populate Vs of_platform_bus_probe. Date: Thu, 01 Nov 2012 10:10:13 +0000 Message-ID: <50924A85.1080907@st.com> References: <50913BC3.7090103@st.com> <5091420D.8050603@gmail.com> Reply-To: srinivas.kandagatla@st.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <5091420D.8050603@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Rob Herring Cc: Grant Likely , "devicetree-discuss@lists.ozlabs.org" , "linux-kernel@vger.kernel.org" List-Id: devicetree@vger.kernel.org On 31/10/12 15:21, Rob Herring wrote: > On 10/31/2012 09:54 AM, Srinivas KANDAGATLA wrote: >> Hi All, >> I have few queries on of_platform_populate and of_platform_bus_probe functions. >> >> Use-case is, I want to explicitly register platform devices from some nodes at post-core or late-init level(like child@1). >> And I don't want of_platform_populate to register platform devices for that node again, so I pass "simple-bus" in match-table. >> Problem is that exiting code for of_platform_populate probes it. >> >> Looking at the function documentation, which states >> of_platform_bus_probe will only create children of the root which are >> selected by the @matches argument. >> >> of_platform_populate walks the device tree and creates devices from >> nodes. It differs in that it follows the modern convention of requiring >> all device nodes to have a 'compatible' property, and it is suitable for >> creating devices which are children of the root node. >> >> Lets say If we call of_platform_populate(NULL, match_table, NULL, NULL) >> on a device trees like the below with >> struct of_device_id match_table[] = { >> { .compatible = "simple-bus", } >> {} >> }; >> >> parent@0{ >> compatible = "xxx,parent1", "simple-bus"; >> ... >> child@0 { >> compatible = "xxx,child0", "simple-bus"; > Well simple-bus here is generally not right unless you want to create > devices for children of child@0. > >> ... >> }; >> child@1 { >> compatible = "xxx,child1"; >> ... >> }; >> child@2 { >> compatible = "xxx,child2", "simple-bus"; >> ... >> }; >> }; >> >> of_platform_bus_probe would create platform-devices for parent@0, >> child@0 and child@2 >> where as >> of_platform_populate would create platform-devices for parent@0, >> child@0, child@1 and child@2 nodes. >> >> So the question is >> why do we need to have @matches argument to of_platform_populate in the >> first place, if it creates all the devices by walking the dt nodes? > The matches is for matching buses, not child devices. > It is assumed you > want to create devices for all 1st level children. Thankyou Rob, my issue solved with the above understanding. I was creating device nodes without any parent, which is why of_platform_populate is probing them. >> It is bit confusing, As some platforms use of_platform_populate(NULL, >> of_default_bus_match_table, NULL, NULL) assuming that only matching >> nodes will end up having platform device. >> Also >> some platforms use of_platform_bus_probe(NULL, match_table, NULL), >> where match table is of_default_bus_match_table. > There should be no new users of of_platform_bus_probe. It is there for > historical reasons on PPC. > >> Am not 100% sure what is the right solution, but I think lot of platforms would want behavior like of_platform_bus_probe which takes lookups aswell. >> If the suggestion is to use of_platform_bus_probe, Which I can't use as It does not take Auxdata(lookups). > of_platform_populate is what you should use. > > Rob > >