On 12/2/2013 5:48 PM, William Hermans wrote: > Charles, where do you get your information from ? Not trying to be rude or > condescending, or anything of that nature. I only ask because I have actual > hands experience with this "feature" and have often wondered if there > could be a potential work around( through code ).
My experience is mostly from beating my head against the wall trying to get this working, along with crawling through some of the device tree "back-story", technical details, and kernel code. Basically, device tree is intended to be a *STATIC* definition of the machine hardware available to the kernel at boot. Pretty much *ALL* device tree does is store a bunch of values that can be retrieved via an identifier (think INI file and you're not too far off). The overlay stuff is all pretty much BeagleBone specific. Loading an overlay works fairly well because it is very similar in concept and process to the kernel initialization...various kernel module code gets run and other kernel modules may or may not already be present or fully loaded. If your driver code can't deal with this, it's going to be buggy in general use, regardless of whether or not you're trying to load overlays. In a sense, loading a device tree overlay is very much like simply extending system initialization for what could be a _long_ time while a bunch of other code runs. :) Unloading an overlay, however, is a minefield of potential problems, particularly since most of the ARM drivers weren't written with hot-plug in mind. I'm not even sure most of the drivers can be unloaded at the kernel level (hmm...I should go off and try to rmmod some of them). Anyway, true hotplug is a big-fat-hairy-can-of-worms, and pretty much _none_ of the ARM ecosystem has been written with hot-plug in mind (except for the bits that carry over from other systems, like USB and PCI). It's not really surprising it crashes, it's just kind of annoying. :) As for a work-around, I believe the saying goes: "There is no problem in computer science which cannot be solved by one more level of indirection." -- Charles Steinkuehler char...@steinkuehler.net -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to beagleboard+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/groups/opt_out.
