On Thu, 18 Feb 2010, Pedro Ribeiro wrote: > Hi all, > > I spent lots of hours trying to figure out why my T400 would not enter > C4 and C6 sleep states. > > Here are my findings: > > - When a USB device is connected, even if it supports USB autosuspend, > the cpu will never go down more than C3 (apparently the mode is > disabled by the BIOS). > > - After removing all the USB devices, in AC it enters C4 and in > battery it enters C6. > The BIOS apparently replaces C3 with C4 and C6, respectively, because > /sys/devices/system/cpu/cpu0/cpuidle/ > > always shows 4 states, whatever the situation. > > So one more reason not to use USB devices while on battery... > > Is this normal behaviour or I have a retarded BIOS? And if so, is > there a workaround? Yes, it is normal, and retarded:-) Ideally, if a USB device is not used and usb autosuspend is successful, then I would hope that you'd be able to get into the deep C-state - but autosuspend is not universally successful; and in some cases does nothing at all. It is common for the BIOS to hide the higher latency deep C-state on AC and expose it on DC. I think that this technique is largely obsolete today, and I'm hopeful that the practice will eventually die out. cheers, -Len Brown, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
