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

From: Shilpasri G Bhat <[email-masked]>
Date: Mon, 10 Aug 2015 13:21:20 +0530

On 08/10/2015 07:11 AM, Stewart Smith wrote:
> Shilpasri G Bhat <[email-masked]> 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.

No we don't export the throttling status of the cpu via sysfs. Since the
throttling state is common across the chip, the per_cpu export will be
redundant. Did you mean something like one of the below:

1)/sys/devices/system/cpu/cpufreq/chipN_throttle

2)/sys/devices/system/cpu/cpuN/cpufreq/throttle

> 
> 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"
> 

Okay will change the messages.

Thanks and Regards,
Shilpa