Hi Guenter,
On 4/5/23 16:15, Guenter Roeck wrote:
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,
At the moment, no. I don't think the regulator subsystem itself requests
shut-down for the system.
As far as I know, the handling of regulator errors is currently done by
regulator consumers. If the only consumers for PMBus regulators are
PMBus specific drivers - then the in-kernel error handling is in the
hands of PMBus specific drivers.
Furthermore, I don't think we have in-tree handling for the regulator
events. Hence, even if there were 'non PMBus specific' consumers for
these regulators - there will probably be no catastrophic things
happening as of now - but if these notifications can leak to non PMBus
regulator consumers, then we place a restriction on handling of these
errors. (Eg, other but PMBus specific regulator consumers must not
handle these).
The one thing to consider is that (as far as I understand) some work has
been done to get these events visible to user-space. I am unsure how the
user-space should know what to do upon these events if these may be
generated for 'different severity' issues.
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 sorry for making the noise here. As I said above, if the only
consumers for these regulators are PMBus devices - then I guess this
does not cause problems. Yet, I wonder if this means that not all of the
regulator notifications should be sent to user-land.
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.
Please, don't block the series if no-one else but me is concerned. It is
highly possible it is me who does not understand the purpose of these
notifications or how they are thought to be handled.
Yours,
-- Matti
--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland
~~ When things go utterly wrong vim users can always type :help! ~~
