Re: powerX_alarm sysfs attribute

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On Thu, 9 Dec 2010 13:26:13 -0800, Ira W. Snyder wrote:
> On Thu, Dec 09, 2010 at 08:58:58AM -0800, Guenter Roeck wrote:
> > Hi all,
> > 
> > I am looking through libsensors and the hwmon sysfs ABI to identify and fix
> > inconsistencies.
> > 
> > One problem I noticed is powerX_alarm, which is defined as "system is drawing
> > more power than the cap allows".
> > 
> > powerX_cap is defined as " ... The *_cap files only appear if the cap is known
> > to be enforced by hardware".
> > 
> > Now there are conditions where power limits are defined and supported,
> > but the hardware does not enforce it. Similar, there are devices reporting power
> > alarms not associated with cap enforcement. Examples are ltc4215 and PMBus devices.
> > powerX_alarm is supported by the ltc4215 driver, but there is no _cap attribute,
> > and the alarm is not associated with a maximum, thus a reported alarm doesn't
> > really reflect the ABI.
> 
> In the ltc4215, the power1_alarm occurs when the output voltage of the
> chip is outside a certain range. This range is specified by external
> resistors, specific to each application. They are not required to be a
> specific value by the hardware.

I am confused. Did you just write _output_ voltage? 

> I guess that the ltc4215 driver's use of powerX_alarm doesn't follow the
> ABI document.

I can confirm that. For one thing, if this has to do with voltage, it's
not a power limit. For another, if it is a voltage _output_ limit, it
has nothing to do with hardware monitoring.

> In essence, the power1_alarm is connected to the chip's power good
> output (negated). Should the ABI have a powerX_good or powerX_fail
> attribute?

-- 
Jean Delvare

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