Re: [Qemu-ppc] [PATCH v5 1/6] ppc: spapr: Register and handle HCALL to receive updated RTAS region

[Nikunj A Dadhania]

David Gibson <address@hidden> writes:

> On Thu, Sep 28, 2017 at 04:07:38PM +0530, Aravinda Prasad wrote:
>> Receive updates from SLOF about the updated rtas-base.
>> A separate patch for SLOF [1] (commit f9a60de3) adds
>> functionality to invoke a private HCALL whenever OS
>> issues instantiate-rtas with a new rtas-base.
>> 
>> This is required as QEMU needs to know the updated rtas-base
>> as it allocates error reporting structure in RTAS space upon
>> a machine check exception.
>> 
>> [1] https://lists.ozlabs.org/pipermail/linuxppc-dev/2014-August/120386.html
>> 
>> Signed-off-by: Aravinda Prasad <address@hidden>
>> Reviewed-by: David Gibson <address@hidden>
>
> Ao I acked this earlier, but I've now realized there might be some
> connection between this and discussions taking place elsewhere about
> qemu not knowing what SLOF does with the device tree.
>
> At what point will SLOF call the UPDATE_RTAS hcall?  I'm guessing at
> the time of instantiate-rtas, is that right?

The call happens from
arch/powerpc/kernel/prom_init.c:prom_instantiate_rtas() and after that
linux kernel makes two entries in the DT

....
       if (call_prom_ret("call-method", 3, 2, &entry,
                          ADDR("instantiate-rtas"),
                          rtas_inst, base) != 0
            || entry == 0) {
                prom_printf(" failed\n");
                return;
        }
        prom_printf(" done\n");

        reserve_mem(base, size);

        val = cpu_to_be32(base);
        prom_setprop(rtas_node, "/rtas", "linux,rtas-base",
                     &val, sizeof(val));
        val = cpu_to_be32(entry);
        prom_setprop(rtas_node, "/rtas", "linux,rtas-entry",
                     &val, sizeof(val));
....

Quiesce is called after this. 

> Does SLOF put the RTAS blob address in its internal device tree, or
> does it only pass it to the guest via the return parameters from
> instantiate-rtas?

Entry was made to the DT by linux kernel prom_init code, will this be
visible to QEMU?

Regards,
Nikunj