Re: [PATCH v3 3/3] Documentation: hwmon: Document the IBM CFF power supply

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On 08/14/2017 01:53 PM, Guenter Roeck wrote:
On Mon, Aug 14, 2017 at 10:26:30AM -0500, Eddie James wrote:
From: "Edward A. James" <eajames@xxxxxxxxxx>

Signed-off-by: Edward A. James <eajames@xxxxxxxxxx>
---
  Documentation/hwmon/ibm-cffps | 54 +++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 54 insertions(+)
  create mode 100644 Documentation/hwmon/ibm-cffps

diff --git a/Documentation/hwmon/ibm-cffps b/Documentation/hwmon/ibm-cffps
new file mode 100644
index 0000000..e091ff2
--- /dev/null
+++ b/Documentation/hwmon/ibm-cffps
@@ -0,0 +1,54 @@
+Kernel driver ibm-cffps
+=======================
+
+Supported chips:
+  * IBM Common Form Factor power supply
+
+Author: Eddie James <eajames@xxxxxxxxxx>
+
+Description
+-----------
+
+This driver supports IBM Common Form Factor (CFF) power supplies. This driver
+is a client to the core PMBus driver.
+
+Usage Notes
+-----------
+
+This driver does not auto-detect devices. You will have to instantiate the
+devices explicitly. Please see Documentation/i2c/instantiating-devices for
+details.
+
+Sysfs entries
+-------------
+
+The following attributes are supported:
+
+curr1_alarm		Output current over-current fault.
+curr1_input		Measured output current in mA.
+curr1_label		"iout1"
+
+fan1_alarm		Fan 1 warning.
+fan1_fault		Fan 1 fault.
+fan1_input		Fan 1 speed in RPM.
+fan2_alarm		Fan 2 warning.
+fan2_fault		Fan 2 fault.
+fan2_input		Fan 2 speed in RPM.
+
+in1_alarm		Input voltage under-voltage fault.
Just noticed. Are you sure you mean 'fault' here and below ?
'alarm' attributes normally report an over- or under- condition,
but not a fault. Faults should be reported with 'fault' attributes.
In PMBus lingo (which doesn't distinguish a real 'fault' from
a critical over- or under- condition), the "FAULT" condition
usually maps with the 'crit_alarm' or 'lcrit_alarm' attributes.
Also, under-voltages would normally be reported as min_alarm
or clrit_alarm, not in_alarm.

Thanks, I better change this doc to "alarm." The spec reports all these as "faults" but many of them are merely over-temp or over-voltage, etc, and should be "alarm" to be consistent with PMBus.

The problem with this power supply is that it doesn't report any "limits." So unless I set up my read_byte function to return some limits, we can't get any lower or upper limits and therefore won't get the crit_alarm, lcrit_alarm, etc. Do you think I should "fake" the limits in the driver?


+in1_input		Measured input voltage in mV.
+in1_label		"vin"
+in2_alarm		Output voltage over-voltage fault.
+in2_input		Measured output voltage in mV.
+in2_label		"vout1"
+
+power1_alarm		Input fault.
Another example; this maps to PMBUS_PIN_OP_WARN_LIMIT which is an
input power alarm, not an indication of a fault condition.

Hm, with my latest changes to look at the higher byte of STATUS_WORD, it looks like we now have the same name for both the pin generic alarm attribute and the pin_limit_attr... So in this device's case, it would map to PB_STATUS_INPUT bit of STATUS_WORD. Didn't think about that... any suggestions? Can't really change the name of the limit one without breaking people's code...


+power1_input		Measured input power in uW.
+power1_label		"pin"
+
+temp1_alarm		PSU inlet ambient temperature over-temperature fault.
+temp1_input		Measured PSU inlet ambient temp in millidegrees C.
+temp2_alarm		Secondary rectifier temp over-temperature fault.
Interestingly, PMBus does not distinguish between a critical temperature
alarm and an actual "fault". Makes me wonder if the IBM PS reports
CFFPS_MFR_THERMAL_FAULT if there is an actual fault (chip or sensor failure),
or if it has the same meaning as PB_TEMP_OT_FAULT, ie an excessively high
temperature.

Will change these to "alarm" in the doc too.


If it is a real fault (a detected sensor failure), we should possibly
consider adding a respective "virtual" temperature status flag. The same
is true for other status bits reported in the manufacturer status
register if any of those reflect a "real" fault, ie a chip failure.

Yea, that would probably be helpful. The CFFPS_MFR_THERMAL_FAULT bit is a fault (so the spec says), but I'm not sure what is triggering it.

Thanks,
Eddie


+temp2_input		Measured secondary rectifier temp in millidegrees C.
+temp3_alarm		ORing FET temperature over-temperature fault.
+temp3_input		Measured ORing FET temperature in millidegrees C.
--
1.8.3.1


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