Syslog message: spmb0 pmbus_read_volt: sfb-07 - MAX20751-PF1-0.9v: pmbus read failed for cmd 0x8b

Summary:

This article explains the meaning of the message, pmbus read failed for cmd 0x8b, which is reported by MX2000-SFB2 (711-052892).

Symptoms:

The following four messages are logged in syslog:

Mar 14 20:45:37.048 2018  MX2000 : %PFE-3: spmb0 PQ3_IIC(WR): no target ack on byte 0 (wait spins 3)
Mar 14 20:45:37.049 2018  MX2000 : %PFE-3: spmb0 PQ3_IIC(WR): I/O error (i2c_stat=0xa3, i2c_ctl[0]=0xb0, bus_addr=0x72)
Mar 14 20:45:37.049 2018  MX2000 : %PFE-3: spmb0 pq3_i2c_smb_read_word: Failed
Mar 14 20:45:37.049 2018  MX2000 : %PFE-3: spmb0 pmbus_read_volt: sfb-07 - MAX20751-PF1-0.9v: pmbus read failed for cmd 0x8b

Cause:

The message is logged when the spmb0 pmbus fails to read the 0.9v voltage sensor value of the MAX20751 IC on SFB07 due to a transient pmbus slow bus transaction.

PR1122480 introduced a retry mechanism (maximum five retry attempts) before declaring bad hardware, but the error message was not completely suppressed.

This message is mostly seen on SFB07, but SFBs in the other slots sometimes report the same message.

Routing Engine 0     REV 05       740-052100       9016092382      RE-S-1800x4
Routing Engine 1     REV 05       740-052100       9016080673      RE-S-1800x4
CB 0                 REV 12       750-063177       ABDP1268        Control Board
CB 1                 REV 12       750-063177       ABDP1266        Control Board
SPMB 0               REV 05       711-041855       ABDP1068        PMB Board
SPMB 1               REV 05       711-041855       ABDP1058        PMB Board
SFB 0                REV 11       711-052892       ABDP1527        Switch Fabric Board 2
SFB 1                REV 11       711-052892       ABDP1518        Switch Fabric Board 2
SFB 2                REV 11       711-052892       ABDT5501        Switch Fabric Board 2
SFB 3                REV 11       711-052892       ABDP0668        Switch Fabric Board 2
SFB 4                REV 11       711-052892       ABDT5523        Switch Fabric Board 2
SFB 5                REV 11       711-052892       ABDP0663        Switch Fabric Board 2
SFB 6                REV 11       711-052892       ABDP0666        Switch Fabric Board 2
SFB 7                REV 11       711-052892       ABDP0658        Switch Fabric Board 2

Solution:

The four syslog messages do not have any traffic impact, and can be ignored. The messages only indicate that the voltage regulator has failed to complete a software read of its current output voltage.

To ignore the four messages (without applying PR1363587), a syslog filter can be configured as follows:

# set system syslog file messages match "!(spmb[01] PQ3_IIC\(WR\): no target ack on byte 0 \(wait spins 3\))| (spmb[01] PQ3_IIC\(WR\): .* bus_addr=0x72)| (spmb[01] pq3_i2c_smb_read_word: Failed)| (spmb[01] pmbus_read_volt: sfb-0[0-7] - MAX20751-PF1-0\.9v: pmbus read failed for cmd 0x8b)"

PR1363587 suppressed the three PQ3 I2C driver messages. So if the fix specified in PR1363587 has been applied, the following syslog filter can suppress the pmbus driver message.

# set system syslog file messages match "!(spmb[01] pmbus_read_volt: sfb-0[0-7] - MAX20751-PF1-0\.9v: pmbus read failed for cmd 0x8b)"

Modification History:

2018-08-01: Solution section updated with PR fix for the syslog message and the updated syslog filter based on the fix. Other minor modifications (non-technical) made

2018-08-17: Filter commands in the Solution have been updated.

Knowledge Base