On Fri, Oct 8, 2021 at 5:31 AM Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx> wrote: > > On Thu, 2021-09-16 at 16:10 +0200, Matthias Schiffer wrote: > > There are situations where it is desirable to use the same base Device > > Tree for devices with a different number of CPUs: There may be CPU > > variants with different numbers of cores that can be used interchangably > > on the same mainboard, or there are multiple CPU sockets. Not needing to > > explicitly build a device tree for each such variant can make > > maintenance significantly easier. > > > > For this to work, a system firmware / bootloader needs to adjust the > > Device Tree by removing or disabling the excess CPU nodes. However, this > > is currently not easily possible due to the special meaning of the > > "disabled" status for CPU nodes: > > > > - A "disabled" CPU node is interpreted as inactive, but existent. The > > Linux kernel will attempt to enable such CPUs on boot, which will > > obviously fail for non-existent CPUs > > - Removing the CPU node altogether from a Device Tree is much more > > complex than setting a single property, as it may leave dangling > > phandle references, often requiring specific knowledge of other nodes' > > structure to deal with them. > > > > In the discussion [1] it was suggested to introduce a new status value > > for CPUs that should really not be used at all. Rob proposed to use the > > value "fail", which already exists in the generic definitions of the > > status property. > > > > [1] https://www.lkml.org/lkml/2020/8/26/1237 > > Hi, > I haven't received any feedback regarding this spec update yet. Should > I also send a kernel patch that actually implements this behaviour? Looks fine to me, just hadn't gotten around to applying. > Do properties described in the spec also need to be documented in the > kernel's Documentation/devicetree/bindings? It seems that there is no > generic "cpu" binding documentation at the moment, only arch-specific > variants. https://github.com/devicetree-org/dt-schema/blob/main/schemas/cpus.yaml Rob
