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

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Message-Id: <0d016c77-4e3e-b9df-b131-604ab6f15e4c@linux.vnet.ibm.com>
Date:   Mon, 14 Aug 2017 14:26:20 -0500
From:   Eddie James <eajames@...ux.vnet.ibm.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     robh+dt@...nel.org, jdelvare@...e.com,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        mark.rutland@....com, devicetree@...r.kernel.org, corbet@....net,
        linux-doc@...r.kernel.org, "Edward A. James" <eajames@...ibm.com>
Subject: Re: [PATCH v3 3/3] Documentation: hwmon: Document the IBM CFF power
 supply



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@...ibm.com>
>>
>> Signed-off-by: Edward A. James <eajames@...ibm.com>
>> ---
>>   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@...ibm.com>
>> +
>> +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
>>