From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johan Hovold Subject: Re: [PATCH 1/3] Input: twl4030-vibra: fix sibling-node lookup Date: Sun, 12 Nov 2017 13:12:35 +0100 Message-ID: <20171112121235.GO11226@localhost> References: <20171111154339.16875-1-johan@kernel.org> <20171111175059.lwfhw2wdhlj5yxhc@dtor-ws> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20171111175059.lwfhw2wdhlj5yxhc@dtor-ws> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Dmitry Torokhov Cc: Johan Hovold , linux-input-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, stable , Peter Ujfalusi , Marek Belisko , Lee Jones , Rob Herring , devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-input@vger.kernel.org [ +CC: Lee, Rob and device-tree list ] On Sat, Nov 11, 2017 at 09:50:59AM -0800, Dmitry Torokhov wrote: > On Sat, Nov 11, 2017 at 04:43:37PM +0100, Johan Hovold wrote: > > A helper purported to look up a child node based on its name was using > > the wrong of-helper and ended up prematurely freeing the parent of-node > > while searching the whole device tree depth-first starting at the parent > > node. > > Ugh, this all is pretty ugly business. Can we teach MFD to allow > specifying firmware node to be attached to the platform devices it > creates in mfd_add_device() so that the leaf drivers simply call > device_property_read_XXX() on their own device and not be bothered with > weird OF refcount issues or what node they need to locate and parse? Yeah, that may have helped. You can actually specify a compatible string in struct mfd_cell today which does make mfd_add_device() associate a matching child node. Some best practice regarding how to deal with MFD and device tree would be good to determine and document too. For example, when should of_platform_populate() be used in favour of mfd_add_device()? And how best to deal with sibling nodes, which is part of the problem here (I think the mfd should have provided a flag rather than having subdrivers deal with sibling nodes, for example). That said, driver authors using the wrong of-helper could possibly have been avoided by amending the kernel docs (I'll do that as a follow up), but once these incorrect usages get in, only review can prevent them from being reproduced through copy-paste coding. Johan -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html