Hi Grant, On May 26, 2014, at 2:23 PM, Grant Likely wrote: > On Mon, 26 May 2014 12:57:32 +0200, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: >> Hi Grant, >> >> On Mon, May 26, 2014 at 12:48 PM, Grant Likely >> <grant.likely@xxxxxxxxxxxx> wrote: >>> On Tue, 20 May 2014 09:38:49 +0200, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote: >>>> On Tue, May 20, 2014 at 7:50 AM, Grant Likely <grant.likely@xxxxxxxxxxxx> wrote: >>>>>> Why has the overlay system been designed for plugging and unpluging whole >>>>>> overlays? >>>>>> That means the kernel has to remember the full stack, causing issues with >>>>>> e.g. kexec. >>>>> >>>>> Mostly so that drivers don't see any difference in the livetree data >>>>> structure. It also means that userspace sees a single representation of >>>>> the hardware at any given time. >>>> >>>> Sorry, I don't follow the argument about the "single representation of the >>>> hardware". >>> >>> Er, s/of the hardware/of the tree/. Right now the overlay design >>> modifies the live tree which at the same time modifies the tree >>> representation in /sys/firmware/devicetree. If the design was changed to >>> keep the overlay logically separate, then I would think we want to >>> expose that information to usespace also. In fact, I think we would need >>> to for usecases like kexec. >> >> OK, so it does modify the real tree, and doesn't keep the actual overlays. >> >> I was under the impression the overlay stack was also kept in memory, to allow >> reversal, so there was a misunderstanding. >> >> Hence for kexec, the tree in /sys/firmware/devicetree can just be passed >> to the new kernel, as that's the current representation of the hardware? > > Heeheehee. We're back where we started. The original question is whether > or not that is a valid approach. If the overlay represents something > that can be hot plugged/unplugged, then passing it through to the second > kernel would be the wrong thing to do. If it was a permenant addition, > then it probably doesn't need to be removed. > > We do actually keep the overlay info in memory for the purpose of > removal exactly so we can support hot unbinding of devices and drivers > that make use of overlays. > We can support either method. I am not feeling any wiser about which one should be the default TBH, so what about exporting a property and let the platform figure out which is more appropriate? > g. > Regards -- Pantelis > -- > 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 -- 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
