On Tue, Oct 10, 2017 at 4:14 PM, Benjamin Herrenschmidt <b...@kernel.crashing.org> wrote: > On Tue, 2017-10-10 at 15:19 +1030, Joel Stanley wrote: >> According to the ASPEED datasheet, gigabit speeds require a clock of >> 100MHz or higher. Other speeds require 25MHz or higher. > > Did you try "live" changing by either using ethtool or plugging into > switches/hubs at different speed ? > > Also this is aspeed'isms, we should probably keep that under an > is_aspeed test. > > My assumption is that we wouldn't bother, and just leave the freq > set based on whether there's a physical gigabit capable connection or > not (ie, real gigabit PHY vs. NC-SI really). But if it can help save a > few milliwatts..
I didn't try changing the link speed at runtime. I don't have a setup that lets me precisely measure power consumption, so it's hard to know what the benefits are. In the future I can revisit this and do those measurements. I'll change it to be as you suggest; 100MHz for PHY and 50MHz for NC-SI. Cheers, Joel