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USB autosuspend in F12

USB is an irritating protocol that requires USB controllers to remain 
active whenever a device is attached, even if that device is doing 
nothing. This consumes unnecessary power and can prevent the system 
going into deep idle states under some circumstances. The kernel 
supports USB autosuspend, which allows idle USB devices to be suspended 
and the upstream ports to power down. This is disabled by default 
because it breaks various pieces of hardware.

Through F12 I'm going to be slowly enabling autosuspend on various 
pieces of USB hardware. The aim is to ensure that it's only enabled on 
hardware that supports it. This is going to be a combination of kernel 
modifications and packaging changes, and while I'll be testing as many 
as possible before uploading anything there's a risk that some hardware 
will misbehave. I'll let people know when I think I'm about to upload 
anything risky.

The first part of this is an upload of libfprint which enables 
autosuspend on fingerprint readers. I'm expecting this to be pretty 
safe, but there's always the possibility that a couple of people will 
find problems. If your fingerprint reader suddenly stops working after 
this change, please file a bug and include the output of lsusb.

Matthew Garrett | mjg59 srcf ucam org

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