[PATCH v2] hwmon: (pmbus/ibm-cffps) Add clear_faults debugfs entry

[Brandon Wyman]

On Wed, Mar 16, 2022 at 3:14 PM Guenter Roeck <linux at roeck-us.net> wrote:
>
> On 3/16/22 13:03, Brandon Wyman wrote:
> > On Sun, Mar 13, 2022 at 11:36 PM Guenter Roeck <linux at roeck-us.net> wrote:
> >>
> >> On 3/11/22 10:10, Brandon Wyman wrote:
> >>> Add a clear_faults write-only debugfs entry for the ibm-cffps device
> >>> driver.
> >>>
> >>> Certain IBM power supplies require clearing some latched faults in order
> >>> to indicate that the fault has indeed been observed/noticed.
> >>>
> >>
> >> That is insufficient, sorry. Please provide the affected power supplies as
> >> well as the affected faults, and confirm that the problem still exists
> >> in v5.17-rc6 or later kernels - or, more specifically, in any kernel which
> >> includes commit 35f165f08950 ("hwmon: (pmbus) Clear pmbus fault/warning
> >> bits after read").
> >>
> >> Thanks,
> >> Guenter
> >
> > Sorry for the delay in responding. I did some testing with commit
> > 35f165f08950. I could not get that code to send the CLEAR_FAULTS
> > command to the power supplies.
> >
> > I can update the commit message to be more specific about which power
> > supplies need this CLEAR_FAULTS sent, and which faults. It is observed
> > with the 1600W power supplies (2B1E model). The faults that latch are
> > the VIN_UV and INPUT faults in the STATUS_WORD. The corresponding
> > STATUS_INPUT fault bits are VIN_UV_FAULT and Unit is Off.
> >
>
> The point is that the respective fault bits should be reset when the
> corresponding alarm attributes are read. This isn't about executing
> a CLEAR_FAULTS command, but about selectively resetting fault bits
> while ensuring that faults are reported at least once. Executing
> CLEAR_FAULTS is a big hammer.
>
> With the patch I pointed to in place, input (and other) faults should
> be reset after the corresponding alarm attributes are read, assuming
> that the condition no longer exists. If that does not happen, we should
> fix the problem instead of deploying the big hammer.
>
> Thanks,
> Guenter

Okay, I see what you are pointing out there. I had been mostly looking
at the "files" in the debugfs paths. Those do not end up running
through that pmbus_get_boolean() function, so the individual fault
clearing was not being attempted. The fault I was interested in
appears to be associated with in1_lcrti_alarm. Reading that will give
me a 1 if there is a VIN_UV fault, and then it sends 0x10 to
STATUS_INPUT. That clears out VIN_UV, but the STATUS_INPUT command was
returning 0x18. Nothing appears to handle clearing BIT(3), that 0x08
mask.

Should there be some kind of define for BIT(3) over in pmbus.h?
Something like PB_VOLTAGE_OFF? Somehow we need something using that in
sbit of the attributes. I had a quick hack that just OR'ed BIT(3) with
BIT(4) for that PB_VOLTAGE_UV_FAULT. That resulted in a clear of both
bits in STATUS_INPUT, and the faults clearing in STATUS_WORD.

It is not clear if there should be a separate alarm for that "Unit Off
For Insufficient Input Voltage", or if the one for in1_lcrit_alarm
could just be the two bits OR'ed into one mask. I can send a patch
with a proposal on how to fix this one bit not getting cleared.

>
> >>
> >>> Signed-off-by: Brandon Wyman <bjwyman at gmail.com>
> >>> ---
> >>> V1 -> V2: Explain why this change is needed
> >>>
> >>>    drivers/hwmon/pmbus/ibm-cffps.c | 11 +++++++++++
> >>>    1 file changed, 11 insertions(+)
> >>>
> >>> diff --git a/drivers/hwmon/pmbus/ibm-cffps.c b/drivers/hwmon/pmbus/ibm-cffps.c
> >>> index e3294a1a54bb..3f02dde02a4b 100644
> >>> --- a/drivers/hwmon/pmbus/ibm-cffps.c
> >>> +++ b/drivers/hwmon/pmbus/ibm-cffps.c
> >>> @@ -67,6 +67,7 @@ enum {
> >>>        CFFPS_DEBUGFS_CCIN,
> >>>        CFFPS_DEBUGFS_FW,
> >>>        CFFPS_DEBUGFS_ON_OFF_CONFIG,
> >>> +     CFFPS_DEBUGFS_CLEAR_FAULTS,
> >>>        CFFPS_DEBUGFS_NUM_ENTRIES
> >>>    };
> >>>
> >>> @@ -274,6 +275,13 @@ static ssize_t ibm_cffps_debugfs_write(struct file *file,
> >>>                if (rc)
> >>>                        return rc;
> >>>
> >>> +             rc = 1;
> >>> +             break;
> >>> +     case CFFPS_DEBUGFS_CLEAR_FAULTS:
> >>> +             rc = i2c_smbus_write_byte(psu->client, PMBUS_CLEAR_FAULTS);
> >>> +             if (rc < 0)
> >>> +                     return rc;
> >>> +
> >>>                rc = 1;
> >>>                break;
> >>>        default:
> >>> @@ -607,6 +615,9 @@ static int ibm_cffps_probe(struct i2c_client *client)
> >>>        debugfs_create_file("on_off_config", 0644, ibm_cffps_dir,
> >>>                            &psu->debugfs_entries[CFFPS_DEBUGFS_ON_OFF_CONFIG],
> >>>                            &ibm_cffps_fops);
> >>> +     debugfs_create_file("clear_faults", 0200, ibm_cffps_dir,
> >>> +                         &psu->debugfs_entries[CFFPS_DEBUGFS_CLEAR_FAULTS],
> >>> +                         &ibm_cffps_fops);
> >>>
> >>>        return 0;
> >>>    }
> >>
>