On Tue, 17 May 2022 at 14:27, Rob Herring <[email protected]> wrote: > > On Thu, May 5, 2022 at 6:41 AM Leif Lindholm <[email protected]> > wrote: > > > > The sbsa-ref machine is continuously evolving. Some of the changes we > > want to make in the near future, to align with real components (e.g. > > the GIC-700), will break compatibility for existing firmware. > > > > Introduce two new properties to the DT generated on machine generation: > > - machine-version-major > > To be incremented when a platform change makes the machine > > incompatible with existing firmware. > > - machine-version-minor > > To be incremented when functionality is added to the machine > > without causing incompatibility with existing firmware. > > to be reset to 0 when machine-version-major is incremented. > > Where's the binding documentation for this? > > We already have a way to version DTs and that's with compatible. I'm > not completely opposed to a version number though, but I am opposed to > it not being common. We've rejected vendors (QCom in fact) doing their > own thing here. > > > > This versioning scheme is *neither*: > > - A QEMU versioned machine type; a given version of QEMU will emulate > > a given version of the platform. > > - A reflection of level of SBSA (now SystemReady SR) support provided. > > FYI, it's planned to certify the virt machine for SR-IR which will > include DT schema validation. Undocumented properties are a problem > for that.
This isn't the 'virt' machine :-) This dtb fragment is a purely private communication between the QEMU model and the sbsa-ref EL3 firmware. We could in theory equally replace it with a set of hardwired "board revision" registers. There's a comment in the existing sources about this: /* * Firmware on this machine only uses ACPI table to load OS, these limited * device tree nodes are just to let firmware know the info which varies from * command line parameters, so it is not necessary to be fully compatible * with the kernel CPU and NUMA binding rules. */ Kernels running on sbsa-ref won't see a dtb (let alone one with this version information in it), because firmware will always boot them with ACPI. thanks -- PMM
