why setpci command cannot configure pci devices successfully?

[feng wind]

Hi,

I try to use setpci utility to modify pci device configuration, but
cannot get result what I expect.

1) setpci -d 8086:107d latency_timer=40 or setpci -s  0002:04:00.0
latency_timer=40
2) setpci -s 0002:04:00.0 latency_timer
 the result is 00

Why setpci fails to modify latency_timer? or how can I change
latency_timer value or other registers?

Any help would be appreciated!

Thanks,

Feng