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

[Zev Weiss <zev@bewilderbeest.net>]

On Thu, Feb 17, 2022 at 04:02:58PM PST, Guenter Roeck wrote:
>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.
>

That sounds like a good idea -- I'll add it in v2.


Thanks,
Zev