On 3/28/23 23:48, Matti Vaittinen wrote:
Hi Naresh, all This mail is maybe more of a question so that I can get on the same page with the rest of the world than anything else. I just have to ask this as I am trying to figure out what kind of handling there could be for regulator errors. I added Mark and couple of others to the CC as I am under the impression they have done some work with the regulator error handling lately :) On 3/28/23 18:03, Naresh Solanki wrote:From: Patrick Rudolph <patrick.rudolph@xxxxxxxxxxxxx> Add regulator events corresponding to regulator error in regulator flag map. Also capture the same in pmbus_regulator_get_flags. Signed-off-by: Patrick Rudolph <patrick.rudolph@xxxxxxxxxxxxx> Signed-off-by: Naresh Solanki <Naresh.Solanki@xxxxxxxxxxxxx> --- drivers/hwmon/pmbus/pmbus_core.c | 74 +++++++++++++++++++++----------- 1 file changed, 49 insertions(+), 25 deletions(-) diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c index d93405f1a495..509bc0ef1706 100644 --- a/drivers/hwmon/pmbus/pmbus_core.c +++ b/drivers/hwmon/pmbus/pmbus_core.c @@ -2693,9 +2693,9 @@ static int pmbus_init_common(struct i2c_client *client, struct pmbus_data *data, return 0; } -/* A PMBus status flag and the corresponding REGULATOR_ERROR_* flag */ +/* A PMBus status flag and the corresponding REGULATOR_ERROR_* and REGULATOR_EVENTS_* flag */ struct pmbus_status_assoc { - int pflag, rflag; + int pflag, rflag, eflag; }; /* PMBus->regulator bit mappings for a PMBus status register */ @@ -2710,27 +2710,36 @@ static const struct pmbus_status_category __maybe_unused pmbus_status_flag_map[] .func = PMBUS_HAVE_STATUS_VOUT, .reg = PMBUS_STATUS_VOUT, .bits = (const struct pmbus_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 }, + { PB_VOLTAGE_UV_WARNING, REGULATOR_ERROR_UNDER_VOLTAGE_WARN, + REGULATOR_EVENT_UNDER_VOLTAGE_WARN }, + { PB_VOLTAGE_UV_FAULT, REGULATOR_ERROR_UNDER_VOLTAGE, + REGULATOR_EVENT_UNDER_VOLTAGE }, + { PB_VOLTAGE_OV_WARNING, REGULATOR_ERROR_OVER_VOLTAGE_WARN, + REGULATOR_EVENT_OVER_VOLTAGE_WARN }, + { PB_VOLTAGE_OV_FAULT, REGULATOR_ERROR_REGULATION_OUT, + REGULATOR_EVENT_OVER_VOLTAGE_WARN },The question I have is: Are these mappings to regulator errors/notifications always correct?
No, they are not always "correct", and can not be, because each chip implements the PMBus standard as they see fit.
(I don't know the PMBUS specification in details - and thus I am _asking_ this here, not telling that the mapping is incorrect). Let me explain why I am asking this. What I have gathered is that at least some ICs allow setting for example 'voltage limits' for different PMBUS over-voltage WARNs/FAULTs. I however don't know if for example the "fatality" of errors indicated by FAULTS vs WARNs is mandated by any specification - or if a hw designers have free hands to decide what these events indicate on their board - or what type of action should be taken when certain ERROR/WARN is emitted.
PMBus actually specifies which action can and should be taken on faults, and that action is configurable. That - again - does not mean, however, that each chip implements this the same way, only that they should. Possible (standard) actions for voltages are: - continue operating without interruption - continue operating for a specified amount of time, then shut down if fault still exists and optionally retry - shut down and optionally retry for a configurable number of times - disable output while fault condition is present (e.g. for temperature faults) and re-enable after fault condition no longer exists Similar configuration settings are defined for current faults, with additional support for current limiting.
Then to the handling of regulator errors: In order to be able to create any handling for the regulator errors/notifications, we should be able to classify the errors/notifications at least by the severity. The very fundamental decision is whether to turn-off the regulator - or even the whole system - in order to protect the hardware from damage. There are few other questions related to error handling as well - for example questions like: Who should handle error? (we may have many consumers?) When should consumer use for example forced regulator-off without knowing the other consumers? When should we have in-kernel handling for errors? When should the errors be sent to user-space trusting someone there is taking care of the situation? Following is largely my own pondering - and I would like to gain better understanding while also avoid sending wrong events/errors for detected HW issues so that we could actually implement recovery actions based on regulator errors / notifications. I have been trying to understand how error handling with regulator events should / could work. In my head (and in the regulator fault detection limit setting) we have 3 severity categories: 1. PROTECTION: The most 'severe' type of issue. This is reserved for cases where the hardware shuts down the regulator(s) without any SW interaction. In most cases there is no need for notification or error status because soc is likely to go down when the power is cut off. Border case is when HW autonomously shuts down a regulator which does not deliver power to any critical component. I am unsure if such situation should be indicated by ERROR level notification. 2. ERROR: Situation where system is no longer usable but the hardware does not do error handling. I would like to suggest that the proper handling for this type of events is regulator or system shutdown. I think the errors/notifications: #define REGULATOR_ERROR_UNDER_VOLTAGE BIT(1) #define REGULATOR_ERROR_OVER_CURRENT BIT(2) #define REGULATOR_ERROR_REGULATION_OUT BIT(3) #define REGULATOR_ERROR_FAIL BIT(4) #define REGULATOR_ERROR_OVER_TEMP BIT(5) #define REGULATOR_EVENT_UNDER_VOLTAGE 0x01 #define REGULATOR_EVENT_OVER_CURRENT 0x02 #define REGULATOR_EVENT_REGULATION_OUT 0x04 #define REGULATOR_EVENT_FAIL 0x08 #define REGULATOR_EVENT_OVER_TEMP 0x10 should only be used to indicate errors with this severity. That would allow actually implementing the handling for these errors. If these errors are sent for "less severe" issues, then we will not be able to do any generic error handling. 3. WARNING: Situation where something is off-the-spec, but system is still thought to be usable. Here some - probably board/system (use-case?) specific - handling may be taking place to prevent things getting worse. I added following flags for this purpose: #define REGULATOR_EVENT_UNDER_VOLTAGE_WARN 0x2000 #define REGULATOR_EVENT_OVER_CURRENT_WARN 0x4000 #define REGULATOR_EVENT_OVER_VOLTAGE_WARN 0x8000 #define REGULATOR_EVENT_OVER_TEMP_WARN 0x10000 #define REGULATOR_EVENT_WARN_MASK 0x1E000 #define REGULATOR_ERROR_UNDER_VOLTAGE_WARN BIT(6) #define REGULATOR_ERROR_OVER_CURRENT_WARN BIT(7) #define REGULATOR_ERROR_OVER_VOLTAGE_WARN BIT(8) #define REGULATOR_ERROR_OVER_TEMP_WARN BIT(9) So, my question(s) are: 1) Is this "classification" sensible and is it still possible? 2) does PMBUS *_WARNING status bits always indicate error which maps to severity WARNING above? And more importantly 3) does PMBUS *_FAULT status bits always indicate error which maps to severity ERROR above? Eg, can we assume correct handling for _FAULT is shutting down the regulator/system?
No, as per above, since PMBus chips implement (or are supposed to implement) their own fault handling.
We have something similar in a few (non PMBUS compatible) PMICs. For example the ROHM BD9576 has a PROTECTION level error detection (automatic shutdown by HW) and then another error detection which just generates an IRQ and allows software to decide what should be done. While writing the driver for that PMIC my thinking was that the decision whether IRQ is indicating a fatal error or a warning should be on the board-designer's table. Thus I implemented it so that the severity and limit configuration for this error is given via device-tree - and it is up to board designer to decide whether the fault is ERROR or WARN - and notification sent by the driver for this IRQ will reflect the given severity. I wonder if something like this is needed for PMBUS - or if we can always say the *_FAULT maps to regulator ERROR and _WARNING maps to regulator WARNING no matter how board using the IC is designed?
In summary, I must admit that I don't entirely understand your questions or why they are tied to PMBus regulator implementations, except that you seem to be saying that because reporting faults to the regulator subsystem as errors may result in shutdowns requested by the regulator subsystem, PMBus chips must not report such faults to the regulator subsystem as errors because that would interfer with fault handling implemented by PMBus chips. I am not sure if PMBus is made an example of here, but it seems to me that I don't have a choice. I'll hold up this series until I have a better understanding of the implications. Guenter
