Re: [PATCH v5 3/6] cpufreq: powernv: Register for OCC related opal_message notification

[Stewart Smith <stewart@linux.vnet.ibm.com>]

Shilpasri G Bhat <shilpa.bhat@linux.vnet.ibm.com> writes:
> diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c
> index d0c18c9..a634199 100644
> --- a/drivers/cpufreq/powernv-cpufreq.c
> +++ b/drivers/cpufreq/powernv-cpufreq.c
> @@ -33,6 +33,7 @@
>  #include <asm/firmware.h>
>  #include <asm/reg.h>
>  #include <asm/smp.h> /* Required for cpu_sibling_mask() in UP configs */
> +#include <asm/opal.h>
>  
>  #define POWERNV_MAX_PSTATES	256
>  #define PMSR_PSAFE_ENABLE	(1UL << 30)
> @@ -41,7 +42,7 @@
>  #define PMSR_LP(x)		((x >> 48) & 0xFF)
>  
>  static struct cpufreq_frequency_table powernv_freqs[POWERNV_MAX_PSTATES+1];
> -static bool rebooting, throttled;
> +static bool rebooting, throttled, occ_reset;
>  
>  static struct chip {
>  	unsigned int id;
> @@ -414,6 +415,74 @@ static struct notifier_block powernv_cpufreq_reboot_nb = {
>  	.notifier_call = powernv_cpufreq_reboot_notifier,
>  };
>  
> +static char throttle_reason[][30] = {
> +					"No throttling",
> +					"Power Cap",
> +					"Processor Over Temperature",
> +					"Power Supply Failure",
> +					"Over Current",
> +					"OCC Reset"
> +				     };
> +
> +static int powernv_cpufreq_occ_msg(struct notifier_block *nb,
> +				   unsigned long msg_type, void *_msg)
> +{
> +	struct opal_msg *msg = _msg;
> +	struct opal_occ_msg omsg;
> +
> +	if (msg_type != OPAL_MSG_OCC)
> +		return 0;
> +
> +	omsg.type = be64_to_cpu(msg->params[0]);
> +
> +	switch (omsg.type) {
> +	case OCC_RESET:
> +		occ_reset = true;
> +		/*
> +		 * powernv_cpufreq_throttle_check() is called in
> +		 * target() callback which can detect the throttle state
> +		 * for governors like ondemand.
> +		 * But static governors will not call target() often thus
> +		 * report throttling here.
> +		 */
> +		if (!throttled) {
> +			throttled = true;
> +			pr_crit("CPU Frequency is throttled\n");
> +		}
> +		pr_info("OCC: Reset\n");
> +		break;
> +	case OCC_LOAD:
> +		pr_info("OCC: Loaded\n");
> +		break;

I wonder if we could have the log messages be a bit clearer here, odds
are, unless you're one of the people reading this code, you have no idea
what an OCC is or what on earth "OCC: Loaded" means and why this
*doesn't* mean that your CPUs are no longer throttled so that your
computer doesn't catch fire/break/add 1+1 and get 4.

Also, do we export this information via sysfs somewhere? It would seem
to want to go along with other cpufreq/cpu info there.

It feels like we could do much better at informing users as to what is
going on.... maybe something like:

"OCC (On Chip Controller - enforces hard thermal/power limits) Resetting: CPU frequency throttled for duration"
"OCC Loading, CPU frequency throttled until OCC started"
"OCC Active, CPU frequency no longer throttled"