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Message-ID: <Yg7cQwA+i5oTYqHJ@hatter.bewilderbeest.net>
Date: Thu, 17 Feb 2022 15:37:39 -0800
From: Zev Weiss <zev@...ilderbeest.net>
To: Guenter Roeck <linux@...ck-us.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 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.
>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.
Thanks for the review,
Zev
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