[lm-sensors] hwmon sysfs API: power attributes and PMBus devices

[lm-sensors] hwmon sysfs API: power attributes and PMBus devices

[Guenter Roeck]

Hi all,

I am currently trying to match PMBus power related capabilities with the sysfs API.
Unfortunately, the power attributes in the sysfs API don't follow the other attributes,
so there is some degree of mismatch.

PMBus supports the following power limit registers:

PMBUS_POUT_OP_FAULT_LIMIT	Output power fault limit
PMBUS_POUT_OP_WARN_LIMIT	Output power warning limit
PMBUS_PIN_OP_WARN_LIMIT		Input power warning limit

the following status bits:

PB_POUT_OP_WARNING		Output power high warning
PB_POUT_OP_FAULT		Output power fault
PB_PIN_OP_WARNING		Input power high warning

and power usage registers for both input and output (PMBUS_READ_PIN and PMBUS_READ_POUT).

The sysfs API currently provides the following power attributes.

Attribute			Matching PMBus register

powerX_input			PMBUS_READ_PIN, PMBUS_READ_POUT
powerX_cap			PMBUS_POUT_OP_WARN_LIMIT / PMBUS_PIN_OP_WARN_LIMIT ?
				Not an exact match, since the API specifically requires
				that "This file only appears if the cap is known
                                to be enforced by hardware".
powerX_alarm			PB_POUT_OP_WARNING / PB_PIN_OP_WARNING ?
				Again not an exact match, since the API again requires
				that "This file only appears if the cap is known
                                to be enforced by hardware".

There is currently no support for powerX_crit (to reflect PMBUS_POUT_OP_FAULT_LIMIT)
and powerX_fault (to reflect PB_POUT_OP_FAULT).

Questions: 
- Can we remove the limitations of powerX_cap and powerX_alarm, ie no longer require
  that the cap has to be enforced by hardware ?
- If not, can we remove the requirement for powerX_alarm, and introduce powerX_max
  to specify an alarm limit ?
  That would actually be more in line with other "_max" attributes, so it might be
  a better solution.
- Can we add new attributes powerX_crit and powerX_fault ?

Guenter

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Re: [lm-sensors] hwmon sysfs API: power attributes and PMBus devices

[Guenter Roeck]

Turns out there is another PMBus register which matches powerX_cap.
Updated list below.

Guenter

On Sun, Jun 27, 2010 at 03:53:29PM -0700, Guenter Roeck wrote:
> Hi all,
> 
> I am currently trying to match PMBus power related capabilities with the sysfs API.
> Unfortunately, the power attributes in the sysfs API don't follow the other attributes,
> so there is some degree of mismatch.
> 
> PMBus supports the following power limit registers:
> 
> PMBUS_POUT_OP_FAULT_LIMIT	Output power fault limit
> PMBUS_POUT_OP_WARN_LIMIT	Output power warning limit
> PMBUS_PIN_OP_WARN_LIMIT		Input power warning limit
> 
> the following status bits:
> 
> PB_POUT_OP_WARNING		Output power high warning
> PB_POUT_OP_FAULT		Output power fault
> PB_PIN_OP_WARNING		Input power high warning
> 
> and power usage registers for both input and output (PMBUS_READ_PIN and PMBUS_READ_POUT).
> 
> The sysfs API currently provides the following power attributes.
> 
> Attribute			Matching PMBus register
> 
> powerX_input			PMBUS_READ_PIN, PMBUS_READ_POUT
> powerX_cap			PMBUS_POUT_OP_WARN_LIMIT / PMBUS_PIN_OP_WARN_LIMIT ?
> 				Not an exact match, since the API specifically requires
> 				that "This file only appears if the cap is known
>                                 to be enforced by hardware".

	The PMBus POUT_MAX register is an exact match to the API.

> powerX_alarm			PB_POUT_OP_WARNING / PB_PIN_OP_WARNING ?
> 				Again not an exact match, since the API again requires
> 				that "This file only appears if the cap is known
>                                 to be enforced by hardware".

	There is also a POWER_LIMITING flag which indicates that the chip is in
	power limiting mode, enforcing POUT_MAX.

> 
> There is currently no support for powerX_crit (to reflect PMBUS_POUT_OP_FAULT_LIMIT)
> and powerX_fault (to reflect PB_POUT_OP_FAULT).

Given the above, there is also no match for the PMBUS_POUT_OP_WARN_LIMIT and
PMBUS_PIN_OP_WARN_LIMIT registers.

> 
> Questions: 
> - Can we remove the limitations of powerX_cap and powerX_alarm, ie no longer require
>   that the cap has to be enforced by hardware ?
	powerX_cap as defined should be retained and is supportable by PMBus devices.

> - If not, can we remove the requirement for powerX_alarm, and introduce powerX_max
>   to specify an alarm limit ?
	Introducing powerX_max would help to support the PMBUS_POUT_OP_WARN_LIMIT
   	and PMBUS_PIN_OP_WARN_LIMIT registers.
	powerX_alarm might then refer to "powerX_cap or powerX_max limit reached".

>   That would actually be more in line with other "_max" attributes, so it might be
>   a better solution.
> - Can we add new attributes powerX_crit and powerX_fault ?
> 
> Guenter

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