Adding critical/fault limits to hwmon sysfs API

Adding critical/fault limits to hwmon sysfs API

[Guenter Roeck]

Hi,

the current hwmon sysfs API does not specify critical or fault limits for voltage
and current readings.

Many recent power controller/monitoring chips have support for such limits in addition
to alarm limits. Typical action, when a the critical or fault limit is reached,
may be a board reset or power shutdown, or to report the fault condition.

Examples for chips supporting critical/fault limits are SMM665 and variants as well
as many PMBus devices, such as MAX8688, MAX16064, LTC2978, and others.

I think it would make sense to add critical/fault limits to the hwmon sysfs API,
to be able to report those limits if supported by a chip.

Any thoughts on this ?

Thanks,
Guenter

Re: [lm-sensors] Adding critical/fault limits to hwmon sysfs API

[Jean Delvare]

Hi Guenter,

On Sun, 20 Jun 2010 09:37:59 -0700, Guenter Roeck wrote:
> the current hwmon sysfs API does not specify critical or fault limits for voltage
> and current readings.
> 
> Many recent power controller/monitoring chips have support for such limits in addition
> to alarm limits. Typical action, when a the critical or fault limit is reached,
> may be a board reset or power shutdown, or to report the fault condition.
> 
> Examples for chips supporting critical/fault limits are SMM665 and variants as well
> as many PMBus devices, such as MAX8688, MAX16064, LTC2978, and others.
> 
> I think it would make sense to add critical/fault limits to the hwmon sysfs API,
> to be able to report those limits if supported by a chip.
> 
> Any thoughts on this ?

I agree it would be good to have standard names (and libsensors
support) if these features are popular. It might be a little difficult
to come up with the right attribute names though.

For temperatures, we have temp[1-*]_crit, for the critical limit on the
high end. We don't have a name for the critical limit on the low end,
because no chip ever implemented that. The name we chose doesn't offer
much possibilities for a nice name while staying consistent. Maybe
"lcrit" would be acceptable for the low end critical limit, and we keep
"crit" for the high end critical limit?

-- 
Jean Delvare

Re: [lm-sensors] Adding critical/fault limits to hwmon sysfs API

[Guenter Roeck]

On Wed, Jun 23, 2010 at 08:43:46AM -0400, Jean Delvare wrote:
> Hi Guenter,
> 
> On Sun, 20 Jun 2010 09:37:59 -0700, Guenter Roeck wrote:
> > the current hwmon sysfs API does not specify critical or fault limits for voltage
> > and current readings.
> > 
> > Many recent power controller/monitoring chips have support for such limits in addition
> > to alarm limits. Typical action, when a the critical or fault limit is reached,
> > may be a board reset or power shutdown, or to report the fault condition.
> > 
> > Examples for chips supporting critical/fault limits are SMM665 and variants as well
> > as many PMBus devices, such as MAX8688, MAX16064, LTC2978, and others.
> > 
> > I think it would make sense to add critical/fault limits to the hwmon sysfs API,
> > to be able to report those limits if supported by a chip.
> > 
> > Any thoughts on this ?
> 
> I agree it would be good to have standard names (and libsensors
> support) if these features are popular. It might be a little difficult
> to come up with the right attribute names though.
> 
> For temperatures, we have temp[1-*]_crit, for the critical limit on the
> high end. We don't have a name for the critical limit on the low end,
> because no chip ever implemented that. The name we chose doesn't offer
> much possibilities for a nice name while staying consistent. Maybe
> "lcrit" would be acceptable for the low end critical limit, and we keep
> "crit" for the high end critical limit?
> 
How about {curr|in|temp}[1-*]_[min_]crit ?

In other words, keep _crit for the upper limit and introduce min_crit for the lower limit.
This would be a bit better aligned with the existing _min while maintaining _crit for the 
upper limit.

Guenter

Re: [lm-sensors] Adding critical/fault limits to hwmon sysfs API

[Jean Delvare]

On Wed, 23 Jun 2010 06:31:47 -0700, Guenter Roeck wrote:
> On Wed, Jun 23, 2010 at 08:43:46AM -0400, Jean Delvare wrote:
> > Hi Guenter,
> > 
> > On Sun, 20 Jun 2010 09:37:59 -0700, Guenter Roeck wrote:
> > > the current hwmon sysfs API does not specify critical or fault limits for voltage
> > > and current readings.
> > > 
> > > Many recent power controller/monitoring chips have support for such limits in addition
> > > to alarm limits. Typical action, when a the critical or fault limit is reached,
> > > may be a board reset or power shutdown, or to report the fault condition.
> > > 
> > > Examples for chips supporting critical/fault limits are SMM665 and variants as well
> > > as many PMBus devices, such as MAX8688, MAX16064, LTC2978, and others.
> > > 
> > > I think it would make sense to add critical/fault limits to the hwmon sysfs API,
> > > to be able to report those limits if supported by a chip.
> > > 
> > > Any thoughts on this ?
> > 
> > I agree it would be good to have standard names (and libsensors
> > support) if these features are popular. It might be a little difficult
> > to come up with the right attribute names though.
> > 
> > For temperatures, we have temp[1-*]_crit, for the critical limit on the
> > high end. We don't have a name for the critical limit on the low end,
> > because no chip ever implemented that. The name we chose doesn't offer
> > much possibilities for a nice name while staying consistent. Maybe
> > "lcrit" would be acceptable for the low end critical limit, and we keep
> > "crit" for the high end critical limit?
> > 
> How about {curr|in|temp}[1-*]_[min_]crit ?
> 
> In other words, keep _crit for the upper limit and introduce min_crit for the lower limit.
> This would be a bit better aligned with the existing _min while maintaining _crit for the 
> upper limit.

I expected a counter-proposal of this kind. The problem I see is that
the new limit we are adding is unrelated to _min. However, the other
_min_* file we have (_min_alarm) expresses something which is relative
to _min. Same as _max_hyst and _crit_hyst, which are relative to _max
and _critn respectively. So I have the feeling that _min_crit sends the
wrong signal to the reader. Especially if we keep _crit for the high
bound, the asymmetry raises questions.

This is my rationale for suggesting _crit and _lcrit. Now, I won't
argue forever if others disagree, these is really only a naming
convention and everything will be fine as long as the drivers and
libsensors agree.

-- 
Jean Delvare

Re: [lm-sensors] Adding critical/fault limits to hwmon sysfs API

[Guenter Roeck]

On Wed, Jun 23, 2010 at 10:29:11AM -0400, Jean Delvare wrote:
> On Wed, 23 Jun 2010 06:31:47 -0700, Guenter Roeck wrote:
> > On Wed, Jun 23, 2010 at 08:43:46AM -0400, Jean Delvare wrote:
> > > Hi Guenter,
> > > 
> > > On Sun, 20 Jun 2010 09:37:59 -0700, Guenter Roeck wrote:
> > > > the current hwmon sysfs API does not specify critical or fault limits for voltage
> > > > and current readings.
> > > > 
> > > > Many recent power controller/monitoring chips have support for such limits in addition
> > > > to alarm limits. Typical action, when a the critical or fault limit is reached,
> > > > may be a board reset or power shutdown, or to report the fault condition.
> > > > 
> > > > Examples for chips supporting critical/fault limits are SMM665 and variants as well
> > > > as many PMBus devices, such as MAX8688, MAX16064, LTC2978, and others.
> > > > 
> > > > I think it would make sense to add critical/fault limits to the hwmon sysfs API,
> > > > to be able to report those limits if supported by a chip.
> > > > 
> > > > Any thoughts on this ?
> > > 
> > > I agree it would be good to have standard names (and libsensors
> > > support) if these features are popular. It might be a little difficult
> > > to come up with the right attribute names though.
> > > 
> > > For temperatures, we have temp[1-*]_crit, for the critical limit on the
> > > high end. We don't have a name for the critical limit on the low end,
> > > because no chip ever implemented that. The name we chose doesn't offer
> > > much possibilities for a nice name while staying consistent. Maybe
> > > "lcrit" would be acceptable for the low end critical limit, and we keep
> > > "crit" for the high end critical limit?
> > > 
> > How about {curr|in|temp}[1-*]_[min_]crit ?
> > 
> > In other words, keep _crit for the upper limit and introduce min_crit for the lower limit.
> > This would be a bit better aligned with the existing _min while maintaining _crit for the 
> > upper limit.
> 
> I expected a counter-proposal of this kind. The problem I see is that
> the new limit we are adding is unrelated to _min. However, the other
> _min_* file we have (_min_alarm) expresses something which is relative
> to _min. Same as _max_hyst and _crit_hyst, which are relative to _max
> and _critn respectively. So I have the feeling that _min_crit sends the
> wrong signal to the reader. Especially if we keep _crit for the high
> bound, the asymmetry raises questions.
> 
> This is my rationale for suggesting _crit and _lcrit. Now, I won't
> argue forever if others disagree, these is really only a naming
> convention and everything will be fine as long as the drivers and
> libsensors agree.

Makes sense. No strong opinion on my side, really. Using crit/lcrit is fine for me as well.
Maybe we should wait if there is input from others and go with lcrit if there is none.

On a side note, libsensors does not support inX_fault today, even though 
it is mentioned in the API, and there is no currX_fault. Likewise, libsensors supports 
currX_alarm but it is not mentioned in hwmon/sysfs-interface.
Unless there are objections, I'll clean that up when I add support for the _[l]crit objects.

Also, lib/sensors.conf.5 has a comment "Likewise, tempX_crit often comes with tempX_max_crit".
Since tempX_max_crit does not exist, it might make sense to remove that comment.

Guenter

Re: [lm-sensors] Adding critical/fault limits to hwmon sysfs API

[Jean Delvare]

Hi Guenter,

On Wed, 23 Jun 2010 08:03:25 -0700, Guenter Roeck wrote:
> On Wed, Jun 23, 2010 at 10:29:11AM -0400, Jean Delvare wrote:
> > I expected a counter-proposal of this kind. The problem I see is that
> > the new limit we are adding is unrelated to _min. However, the other
> > _min_* file we have (_min_alarm) expresses something which is relative
> > to _min. Same as _max_hyst and _crit_hyst, which are relative to _max
> > and _critn respectively. So I have the feeling that _min_crit sends the
> > wrong signal to the reader. Especially if we keep _crit for the high
> > bound, the asymmetry raises questions.
> > 
> > This is my rationale for suggesting _crit and _lcrit. Now, I won't
> > argue forever if others disagree, these is really only a naming
> > convention and everything will be fine as long as the drivers and
> > libsensors agree.
> 
> Makes sense. No strong opinion on my side, really. Using crit/lcrit is fine for me as well.
> Maybe we should wait if there is input from others and go with lcrit if there is none.

OK, fine with me.

> On a side note, libsensors does not support inX_fault today, even though 
> it is mentioned in the API, and there is no currX_fault. Likewise, libsensors supports 
> currX_alarm but it is not mentioned in hwmon/sysfs-interface.
> Unless there are objections, I'll clean that up when I add support for the _[l]crit objects.

Yes, please!

> Also, lib/sensors.conf.5 has a comment "Likewise, tempX_crit often comes with tempX_max_crit".
> Since tempX_max_crit does not exist, it might make sense to remove that comment.

Does the sentence make sense if you replace tempX_max_crit with
tempX_crit_hyst? Looks like a copy-paste-edit mistake (that would be
from me.)

-- 
Jean Delvare

Re: [lm-sensors] Adding critical/fault limits to hwmon sysfs API

[Guenter Roeck]

On Wed, Jun 23, 2010 at 12:34:37PM -0400, Jean Delvare wrote:
> Hi Guenter,
> 
> On Wed, 23 Jun 2010 08:03:25 -0700, Guenter Roeck wrote:
> > On Wed, Jun 23, 2010 at 10:29:11AM -0400, Jean Delvare wrote:
> > > I expected a counter-proposal of this kind. The problem I see is that
> > > the new limit we are adding is unrelated to _min. However, the other
> > > _min_* file we have (_min_alarm) expresses something which is relative
> > > to _min. Same as _max_hyst and _crit_hyst, which are relative to _max
> > > and _critn respectively. So I have the feeling that _min_crit sends the
> > > wrong signal to the reader. Especially if we keep _crit for the high
> > > bound, the asymmetry raises questions.
> > > 
> > > This is my rationale for suggesting _crit and _lcrit. Now, I won't
> > > argue forever if others disagree, these is really only a naming
> > > convention and everything will be fine as long as the drivers and
> > > libsensors agree.
> > 
> > Makes sense. No strong opinion on my side, really. Using crit/lcrit is fine for me as well.
> > Maybe we should wait if there is input from others and go with lcrit if there is none.
> 
> OK, fine with me.
> 
> > On a side note, libsensors does not support inX_fault today, even though 
> > it is mentioned in the API, and there is no currX_fault. Likewise, libsensors supports 
> > currX_alarm but it is not mentioned in hwmon/sysfs-interface.
> > Unless there are objections, I'll clean that up when I add support for the _[l]crit objects.
> 
> Yes, please!
> 
> > Also, lib/sensors.conf.5 has a comment "Likewise, tempX_crit often comes with tempX_max_crit".
> > Since tempX_max_crit does not exist, it might make sense to remove that comment.
> 
> Does the sentence make sense if you replace tempX_max_crit with
> tempX_crit_hyst? Looks like a copy-paste-edit mistake (that would be
> from me.)

Yes, I think that is the problem. I'll fix that together with the other changes.

Guenter

Re: [lm-sensors] Adding critical/fault limits to hwmon sysfs API

[Mark Brown]

On Wed, Jun 23, 2010 at 02:43:46PM +0200, Jean Delvare wrote:

> For temperatures, we have temp[1-*]_crit, for the critical limit on the
> high end. We don't have a name for the critical limit on the low end,
> because no chip ever implemented that. The name we chose doesn't offer

FWIW battery monitoring chips are likely to implement under temperature
warnings - the Wolfson chargers do, for example.  Low temperature can be
as problematic as high temperature for the chemistry.

Re: [lm-sensors] Adding critical/fault limits to hwmon sysfs API

[Jean Delvare]

On Thu, 24 Jun 2010 01:09:17 +0100, Mark Brown wrote:
> On Wed, Jun 23, 2010 at 02:43:46PM +0200, Jean Delvare wrote:
> 
> > For temperatures, we have temp[1-*]_crit, for the critical limit on the
> > high end. We don't have a name for the critical limit on the low end,
> > because no chip ever implemented that. The name we chose doesn't offer
> 
> FWIW battery monitoring chips are likely to implement under temperature
> warnings - the Wolfson chargers do, for example.  Low temperature can be
> as problematic as high temperature for the chemistry.

We already have temp[1-*]_min. We would have to add temp[1-*]_lcrit
only if a chip has 2 lower limits, one which is only a warning and one
which is critical.

-- 
Jean Delvare