Some platforms such as hifive unmatched doesn't implement mcountinhibit csr. However, it has hardware events that can be monitored using 2 hpmcounter it has (i.e. mhpmcounter3 & mhpmcounter4). Currently, PMU extension disabled if mcountinhibit is absent. That's not really necessary as long as the supervisor OS keeps track of the delta value of the counters. Without mcountinhibit, the delta value won't be entirely accurate because the counters are freely running. However, that should be fine to produce an approximate counter value which can help performance analysis. Perf sampling won't work though as sscof extension is not present in hifive unmatched. Reviewed-by: Anup Patel <anup.patel@wdc.com> Reviewed-by: Bin Meng <bmeng.cn@gmail.com> Signed-off-by: Atish Patra <atish.patra@wdc.com>