Re: [PATCH 1/4] hwmon: (pmbus) Add get_error_flags support to regulator ops

[Guenter Roeck <linux@roeck-us.net>]

On 2/17/22 15:37, Zev Weiss wrote:
> On Thu, Feb 17, 2022 at 10:11:32AM PST, Guenter Roeck wrote:
>> On 2/17/22 02:44, Zev Weiss wrote:
>>> The various PMBus status bits don't all map perfectly to the more
>>> limited set of REGULATOR_ERROR_* flags, but there's a reasonable
>>> number where they correspond well enough.
>>>
>>> Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
>>> ---
>>>  drivers/hwmon/pmbus/pmbus_core.c | 97 ++++++++++++++++++++++++++++++++
>>>  1 file changed, 97 insertions(+)
>>>
>>> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
>>> index 776ee2237be2..a274e8e524a5 100644
>>> --- a/drivers/hwmon/pmbus/pmbus_core.c
>>> +++ b/drivers/hwmon/pmbus/pmbus_core.c
>>> @@ -2417,10 +2417,107 @@ static int pmbus_regulator_disable(struct regulator_dev *rdev)
>>>      return _pmbus_regulator_on_off(rdev, 0);
>>>  }
>>> +/* A PMBus status flag and the corresponding REGULATOR_ERROR_* flag */
>>> +struct pmbus_regulator_status_assoc {
>>> +    int pflag, rflag;
>>> +};
>>> +
>>> +/* PMBus->regulator bit mappings for a PMBus status register */
>>> +struct pmbus_regulator_status_category {
>>> +    int func;
>>> +    int reg;
>>> +    const struct pmbus_regulator_status_assoc *bits; /* zero-terminated */
>>> +};
>>> +
>>> +static const struct pmbus_regulator_status_category pmbus_regulator_flag_map[] = {
>>> +    {
>>> +        .func = PMBUS_HAVE_STATUS_VOUT,
>>> +        .reg = PMBUS_STATUS_VOUT,
>>> +        .bits = (const struct pmbus_regulator_status_assoc[]) {
>>> +            { PB_VOLTAGE_UV_WARNING, REGULATOR_ERROR_UNDER_VOLTAGE_WARN },
>>> +            { PB_VOLTAGE_UV_FAULT,   REGULATOR_ERROR_UNDER_VOLTAGE },
>>> +            { PB_VOLTAGE_OV_WARNING, REGULATOR_ERROR_OVER_VOLTAGE_WARN },
>>> +            { PB_VOLTAGE_OV_FAULT,   REGULATOR_ERROR_REGULATION_OUT },
>>> +            { },
>>> +        },
>>> +    }, {
>>> +        .func = PMBUS_HAVE_STATUS_IOUT,
>>> +        .reg = PMBUS_STATUS_IOUT,
>>> +        .bits = (const struct pmbus_regulator_status_assoc[]) {
>>> +            { PB_IOUT_OC_WARNING,    REGULATOR_ERROR_OVER_CURRENT_WARN },
>>> +            { PB_IOUT_OC_FAULT,      REGULATOR_ERROR_OVER_CURRENT },
>>> +            { PB_IOUT_OC_LV_FAULT,   REGULATOR_ERROR_OVER_CURRENT },
>>> +            { },
>>> +        },
>>> +    }, {
>>> +        .func = PMBUS_HAVE_STATUS_TEMP,
>>> +        .reg = PMBUS_STATUS_TEMPERATURE,
>>> +        .bits = (const struct pmbus_regulator_status_assoc[]) {
>>> +            { PB_TEMP_OT_WARNING,    REGULATOR_ERROR_OVER_TEMP_WARN },
>>> +            { PB_TEMP_OT_FAULT,      REGULATOR_ERROR_OVER_TEMP },
>>> +            { },
>>> +        },
>>> +    },
>>> +};
>>> +
>>> +static int pmbus_regulator_get_error_flags(struct regulator_dev *rdev, unsigned int *flags)
>>> +{
>>> +    int i, status, statusreg;
>>> +    const struct pmbus_regulator_status_category *cat;
>>> +    const struct pmbus_regulator_status_assoc *bit;
>>> +    struct device *dev = rdev_get_dev(rdev);
>>> +    struct i2c_client *client = to_i2c_client(dev->parent);
>>> +    struct pmbus_data *data = i2c_get_clientdata(client);
>>> +    u8 page = rdev_get_id(rdev);
>>> +    int func = data->info->func[page];
>>> +
>>> +    *flags = 0;
>>> +
>>> +    for (i = 0; i < ARRAY_SIZE(pmbus_regulator_flag_map); i++) {
>>> +        cat = &pmbus_regulator_flag_map[i];
>>> +        if (!(func & cat->func))
>>> +            continue;
>>> +
>>> +        status = pmbus_read_byte_data(client, page, cat->reg);
>>> +        if (status < 0)
>>> +            return status;
>>> +
>>> +        for (bit = cat->bits; bit->pflag; bit++) {
>>> +            if (status & bit->pflag)
>>> +                *flags |= bit->rflag;
>>> +        }
>>> +    }
>>> +
>>> +    /*
>>> +     * Map what bits of STATUS_{WORD,BYTE} we can to REGULATOR_ERROR_*
>>> +     * bits.  Some of the other bits are tempting (especially for cases
>>> +     * where we don't have the relevant PMBUS_HAVE_STATUS_*
>>> +     * functionality), but there's an unfortunate ambiguity in that
>>> +     * they're defined as indicating a fault *or* a warning, so we can't
>>> +     * easily determine whether to report REGULATOR_ERROR_<foo> or
>>> +     * REGULATOR_ERROR_<foo>_WARN.
>>> +     */
>>> +    statusreg = data->has_status_word ? PMBUS_STATUS_WORD : PMBUS_STATUS_BYTE;
>>> +    status = pmbus_get_status(client, page, statusreg);
>>> +
>>
>> pmbus_get_status() calls data->read_status if PMBUS_STATUS_WORD is provided
>> as parameter, and data->read_status is set to pmbus_read_status_byte()
>> if reading the word status is not supported. Given that, why not just call
>> pmbus_get_status(client, page, PMBUS_STATUS_WORD) ?
> 
> Good point, I'll change it to do that instead.  (And send v2 separately from the power-efuse driver patches.)
> 
>>
>>> +    if (status < 0)
>>> +        return status;
>>> +
>>> +    if (pmbus_regulator_is_enabled(rdev) && (status & PB_STATUS_OFF))
>>> +        *flags |= REGULATOR_ERROR_FAIL;
>>> +    if (status & PB_STATUS_IOUT_OC)
>>> +        *flags |= REGULATOR_ERROR_OVER_CURRENT;
>>
>> If the current status register is supported, this effectively means that
>> an overcurrent warning is always reported as both REGULATOR_ERROR_OVER_CURRENT
>> and REGULATOR_ERROR_OVER_CURRENT_WARN. Is that intentional ?
>>
> 
> No, but I don't think (by my reading of the spec) that's what would happen?
> 
> I'm looking at table 16 ("STATUS_WORD Message Contents") in section 17.2 ("STATUS_WORD") of Part II of revision 1.3.1 of the PMBus spec, which says that bit 4 of the low byte (PB_STATUS_IOUT_OC) indicates an output overcurrent fault, not a warning (in contrast to most of the other bits, which may indicate either).
> 
>>
>>> +    if (status & PB_STATUS_VOUT_OV)
>>> +        *flags |= REGULATOR_ERROR_REGULATION_OUT;
>>
>> Same for voltage.
> 
> Likewise, PB_STATUS_VOUT_OV is specified as indicating a fault, not a warning.
> 

Ok, that makes sense.

>> On the other side, temperature limit violations are not
>> reported at all unless the temperature status register exists.
>> That seems to be a bit inconsistent to me.
>>
> 
> Right -- that's because PB_STATUS_TEMPERATURE is one of the "fault or warning" bits (unlike VOUT_OV and IOUT_OC), and hence it's an ambiguous case as described in the comment before the pmbus_get_status() call.
> 
> It's certainly not ideal, but it seemed like the best approach I could see given the semantics of the available flags -- I'm open to other possibilities though if there's something else that would work better.
> 

My approach would be to report a warning if no temperature warning/fault
is set from PMBUS_STATUS_TEMPERATURE but PB_STATUS_TEMPERATURE is set
in the status register.

Something like

	if (!(*flags & (REGULATOR_ERROR_OVER_TEMP | REGULATOR_ERROR_OVER_TEMP_WARN))
	    && (status & PB_STATUS_TEMPERATURE))
		*flags |= REGULATOR_ERROR_OVER_TEMP_WARN;

While not perfect, it would be better than reporting nothing.

Guenter