Alexey Kardashevskiy <a...@ozlabs.ru> writes:
> The PAPR+ specification defines a ibm,client-architecture-support (CAS)
> RTAS call which purpose is to provide a negotiation mechanism for
> the guest and the hypervisor to work out the best compatibility parameters.
> During the negotiation process, the guest provides an array of various
> options and capabilities which it supports, the hypervisor adjusts
> the device tree and (optionally) reboots the guest.
>
> At the moment the Linux guest calls CAS method at early boot so SLOF
> gets called. SLOF allocates a memory buffer for the device tree changes
> and calls a custom KVMPPC_H_CAS hypercall. QEMU parses the options,
> composes a diff for the device tree, copies it to the buffer provided
> by SLOF and returns to SLOF. SLOF updates the device tree and returns
> control to the guest kernel. Only then the Linux guest parses the device
> tree so it is possible to avoid unnecessary reboot in most cases.
>
> The device tree diff is a header with the update format version
> (defined as 0 in this patch)
That is 1 in the code.
> @@ -562,6 +563,31 @@ static void *spapr_create_fdt_skel(hwaddr initrd_base,
> return fdt;
> }
>
> +int spapr_h_cas_compose_response(target_ulong addr, target_ulong size)
> +{
> + void *fdt;
> + sPAPRDeviceTreeUpdateHeader hdr = { .version_id = 1 };
> +
Regards
Nikunj
