Comment 6 for bug 1394163

Here's a couple of possibilities.

First of all, iwconfig uses wireless extensions, which is deprecated but supported through emulation. I'm honestly not sure whether changing the power save option is expected to work that way. Try using 'sudo iw wlan0 get power_save" for reading the power save state and 'sudo iw wlan0 set powersave <state>" to set it, where <state> is either on or off.

The other possibility is that the ath9k.ps_enable is set then it's going to fail exactly as you describe. Please run 'cat /sys/module/ath9k/parameters/ps_enable'. I'm not sure off the top of my head what this will output, but if it's something like "1" or "yes" or "true" or "on" that means the flag is set and any attempt to change the power save state will fail in this manner. If it outputs something like "0" or "no" or "false" or "off" then the commands should succeed, even if you aren't changing the state.