On Sun, 12 Nov 2017, Johan Hovold wrote: > [ +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? If a child compatible is provided, we already set the child's of_node. It's then up to the driver (set) author(s) to use it in the correct manner. > 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()? When the device supports DT and its entire hierarchical layout, along with all of its attributes can be expressed in DT. > 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). I disagree. The only properties the MFD (parent) driver is interested in is ones which are shared across multiple child devices. *Everything* which pertains to only a single child device should be handled by its accompanying driver. > 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. -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- 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
