[PATCH] hwmon: (pmbus) delta-ahe50dc-fan: work around hardware quirk

Zev Weiss
2022-04-27T03:51:40Z

CLEAR_FAULTS commands can apparently sometimes trigger catastrophic
power output glitches on the ahe-50dc, so block them from being sent
at all.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Cc: stable@vger.kernel.org
---
drivers/hwmon/pmbus/delta-ahe50dc-fan.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/drivers/hwmon/pmbus/delta-ahe50dc-fan.c b/drivers/hwmon/pmbus/delta-ahe50dc-fan.c
index 40dffd9c4cbf..f546f0c12497 100644
--- a/drivers/hwmon/pmbus/delta-ahe50dc-fan.c
+++ b/drivers/hwmon/pmbus/delta-ahe50dc-fan.c
@@ -14,6 +14,21 @@

#define AHE50DC_PMBUS_READ_TEMP4 0xd0

+static int ahe50dc_fan_write_byte(struct i2c_client *client, int page, u8 value)
+{
+ /*
+ * The CLEAR_FAULTS operation seems to sometimes (unpredictably, perhaps
+ * 5% of the time or so) trigger a problematic phenomenon in which the
+ * fan speeds surge momentarily and at least some (perhaps all?) of the
+ * system's power outputs experience a glitch.
+ *
+ * However, according to Delta it should be OK to simply not send any
+ * CLEAR_FAULTS commands (the device doesn't seem to be capable of
+ * reporting any faults anyway), so just blackhole them unconditionally.
+ */
+ return value == PMBUS_CLEAR_FAULTS ? -EOPNOTSUPP : -ENODATA;
+}
+
static int ahe50dc_fan_read_word_data(struct i2c_client *client, int page, int phase, int reg)
{
/* temp1 in (virtual) page 1 is remapped to mfr-specific temp4 */
@@ -68,6 +83,7 @@ static struct pmbus_driver_info ahe50dc_fan_info = {
PMBUS_HAVE_VIN | PMBUS_HAVE_FAN12 | PMBUS_HAVE_FAN34 |
PMBUS_HAVE_STATUS_FAN12 | PMBUS_HAVE_STATUS_FAN34 | PMBUS_PAGE_VIRTUAL,
.func[1] = PMBUS_HAVE_TEMP | PMBUS_PAGE_VIRTUAL,
+ .write_byte = ahe50dc_fan_write_byte,
.read_word_data = ahe50dc_fan_read_word_data,
};

--
2.36.0