Re: [PATCH 2/5] ppc/pnv: Add support for NMI interface

[Nicholas Piggin <npiggin@gmail.com>]

Cédric Le Goater's on March 26, 2020 2:38 am:
> [ Please use clg@kaod.org ! ]
> 
> On 3/25/20 3:41 PM, Nicholas Piggin wrote:
>> This implements the NMI interface for the PNV machine, similarly to
>> commit 3431648272d ("spapr: Add support for new NMI interface") for
>> SPAPR.
>> 
>> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> 
> one minor comment,
> 
> Reviewed-by: Cédric Le Goater <clg@kaod.org>
> 
>> ---
>>  hw/ppc/pnv.c | 30 +++++++++++++++++++++++++++++-
>>  1 file changed, 29 insertions(+), 1 deletion(-)
>> 
>> diff --git a/hw/ppc/pnv.c b/hw/ppc/pnv.c
>> index b75ad06390..671535ebe6 100644
>> --- a/hw/ppc/pnv.c
>> +++ b/hw/ppc/pnv.c
>> @@ -27,6 +27,7 @@
>>  #include "sysemu/runstate.h"
>>  #include "sysemu/cpus.h"
>>  #include "sysemu/device_tree.h"
>> +#include "sysemu/hw_accel.h"
>>  #include "target/ppc/cpu.h"
>>  #include "qemu/log.h"
>>  #include "hw/ppc/fdt.h"
>> @@ -34,6 +35,7 @@
>>  #include "hw/ppc/pnv.h"
>>  #include "hw/ppc/pnv_core.h"
>>  #include "hw/loader.h"
>> +#include "hw/nmi.h"
>>  #include "exec/address-spaces.h"
>>  #include "qapi/visitor.h"
>>  #include "monitor/monitor.h"
>> @@ -1955,10 +1957,35 @@ static void pnv_machine_set_hb(Object *obj, bool value, Error **errp)
>>      }
>>  }
>> 
>> +static void pnv_cpu_do_nmi_on_cpu(CPUState *cs, run_on_cpu_data arg)
>> +{
>> +    PowerPCCPU *cpu = POWERPC_CPU(cs);
>> +    CPUPPCState *env = &cpu->env;
>> +
>> +    cpu_synchronize_state(cs);
>> +    ppc_cpu_do_system_reset(cs);
>> +    /*
>> +     * SRR1[42:45] is set to 0100 which the ISA defines as implementation
> 
> I see 'System Reset' in ISA 3.0
>> +     * dependent. POWER processors use this for xscom triggered interrupts,
>> +     * which come from the BMC or NMI IPIs.
>> +     */
>> +    env->spr[SPR_SRR1] |= PPC_BIT(43);
> 
> So we could have used the skiboot SPR_SRR1_PM_WAKE_SRESET define ? 

Ah, that's only for power-saving wakeup. But you got me to dig further
and I think I've got a few things wrong here.

The architectural power save wakeup due to sreset bit 43 needs to be
set, probably in excp_helper.c if (msr_pow) test.

    case POWERPC_EXCP_RESET:     /* System reset exception                   */
        /* A power-saving exception sets ME, otherwise it is unchanged */
        if (msr_pow) {
            /* indicate that we resumed from power save mode */
            msr |= 0x10000;
            new_msr |= ((target_ulong)1 << MSR_ME);
        }

For non-power save wakeup, it's all implementation defined. POWER9 UM 
has the table, but I got the damn bit wrong, I was probably looking in
the ISA table by mistake. It's bit 44 for that case. Linux doesn't tend 
to care about that case, but it does care about the power save wakeup
case, so this patch seems to generally "work", but I'll have to fix it.

Thanks,
Nick