[Skiboot] [PATCH] hw/imc: pause imc ucode at boot

Stewart Smith stewart at linux.vnet.ibm.com
Tue Oct 10 13:35:35 AEDT 2017


Madhavan Srinivasan <maddy at linux.vnet.ibm.com> writes:
> IMC nest counters has both in-band (ucode) and out of
> band access to it. Since not all nest counter configurations
> are supported by ucode, out of band tools are used to
> characterize other configuration.
>
> So it is prefer to pause the nest microcode at boot to aid the
> out of band tools. If the ucode not paused and OS does not
> have IMC driver support, then out to band tools will race with
> ucode and end up getting undesirable values. Patch to check and
> pause the ucode at boot.

Please also mention how this works with the OPAL API as the API is that
OPAL_IMC_COUNTERS_INIT and START must be called for any counters that the OS
wants to use.

So, really, we were allowing buggy OSs to work as we were starting with
some counters running.

> Signed-off-by: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>
> ---
> Currently only Linux driver support In-Memory Collection counter
> hardware, which do pause the nest imc counters during driver
> initialisation. So this change should not have any impact.
>
>  hw/imc.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
>
> diff --git a/hw/imc.c b/hw/imc.c
> index 10505f69d4bd..6f92c60d285d 100644
> --- a/hw/imc.c
> +++ b/hw/imc.c
> @@ -128,6 +128,18 @@ static bool is_nest_mem_initialized(struct imc_chip_cb *ptr)
>  	return true;
>  }
>
> +static void pause_microcode_at_boot(void)
> +{
> +	struct proc_chip *chip;
> +	struct imc_chip_cb *cb;
> +
> +	for_each_chip(chip) {
> +		cb = (struct imc_chip_cb *)(chip->homer_base + P9_CB_STRUCT_OFFSET);
> +		if (is_nest_mem_initialized(cb))
> +			cb->imc_chip_command =  cpu_to_be64(NEST_IMC_DISABLE);
> +	}
> +}

get_imc_cb() does all of this logic.

The command here doesn't have the mambo quirk that
opal_imc_counters_stop() has.

> +
>  /*
>   * A Quad contains 4 cores in Power 9, and there are 4 addresses for
>   * the Core Hardware Trace Macro (CHTM) attached to each core.
> @@ -543,6 +555,18 @@ imc_mambo:
>  		return;
>
>  	/*
> +	 * IMC nest counters has both in-band (ucode access) and out of band
> +	 * access to it. Since not all nest counter configurations are supported
> +	 * by ucode, out of band tools are used to characterize other
> +	 * configuration.
> +	 *
> +	 * If the ucode not paused and OS does not have IMC driver support,
> +	 * then out to band tools will race with ucode and end up getting
> +	 * undesirable values. Hence pause the ucode if it is already running.
> +	 */
> +	pause_microcode_at_boot();
> +
> +	/*
>  	 * If the dt_attach_root() fails, "imc-counters" node will not be
>  	 * seen in the device-tree and hence OS should not make any
>  	 * OPAL_IMC_* calls.
> -- 
> 2.7.4
>

-- 
Stewart Smith
OPAL Architect, IBM.



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