[Skiboot] [PATCH v8 07/10] skiboot: Add opal call to enable/disable Nest IMC

[Michael Ellerman]

Madhavan Srinivasan <maddy at linux.vnet.ibm.com> writes:

> diff --git a/hw/imc.c b/hw/imc.c
> index 76b9659b752d..8436fa3933f6 100644
> --- a/hw/imc.c
> +++ b/hw/imc.c
> @@ -255,3 +255,58 @@ err:
>  	prerror("IMC Devices not added\n");
>  	free(buf);
>  }
> +
> +/*
> + * opal_nest_imc_counters_control : This call controls the nest IMC microcode.
> + *
> + * mode      : For now, this call supports only OPAL_NEST_IMC_PRODUCTION_MODE.
> + *             This mode can start/stop the Nest IMC Microcode for nest
> + *             instrumentation from Host OS.
> + * operation : Start(0x0) or Stop(0x1) the engine.
> + *
> + * This call can be extended to include more operations to use the multiple
> + * debug modes provided by the nest IMC microcode and the parameters value_1
> + * and value_2 for the same purpose.
> + */
> +static int64_t opal_nest_imc_counters_control(uint64_t mode,
> +					      uint64_t operation,
> +					      uint64_t value_1,
> +					      uint64_t value_2)
> +{

Sorry but I don't like this API at all.

Am I counting right that this gives us 73,786,976,294,838,206,464
possible combinations of parameters? :)

There's also no good way for Linux to know what values of mode,
operation, value1 or value2 are supported by the currently running OPAL.

I don't see why we wouldn't just have two OPAL calls, start and stop.

If we want to add another mode in future, that can be a new OPAL call.
Linux can detect a new OPAL call easily & cleanly with OPAL_CHECK_TOKEN.

cheers