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Date: Thu, 17 Feb 2022 16:02:58 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Zev Weiss <zev@...ilderbeest.net>
Cc: Jean Delvare <jdelvare@...e.com>, linux-hwmon@...r.kernel.org,
openbmc@...ts.ozlabs.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>,
Liam Girdwood <lgirdwood@...il.com>
Subject: Re: [PATCH 1/4] hwmon: (pmbus) Add get_error_flags support to
regulator ops
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@...ilderbeest.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
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