Comment 0 for bug 1811200

[Impact]
No driver for PMU of L3 cache controller (L3C) and the DDR4 Memory Controller (DMC) for Cavium ThunderX2 SoC

[Test Case]
sudo perf stat -a -e \
> uncore_dmc_0/cnt_cycles/,\
> uncore_dmc_0/data_transfers/,\
> uncore_dmc_0/read_txns/,\
> uncore_dmc_0/write_txns/ sleep 1

sudo perf stat -a -e \
> uncore_l3c_0/read_request/,\
> uncore_l3c_0/read_hit/,\
> uncore_l3c_0/inv_request/,\
> uncore_l3c_0/inv_hit/ sleep 1

sudo perf stat -a -e uncore_dmc_0/cnt_cycles/ sleep 1

[Fix]
Backport patches
82975c46da perf: Export perf_event_update_userpage
d6310a3f33 Documentation: perf: Add documentation for ThunderX2 PMU uncore driver
69c32972d5 drivers/perf: Add Cavium ThunderX2 SoC UNCORE PMU driver
and enable CONFIG_THUNDERX2_PMU=m

[Regression Risk]
This driver only loaded when CAV901C in ACPI table, lowest risk for other platform.