Move USB autosuspend policy to userspace

David:

Lately we've been seeing more and more USB devices that can't handle 
being suspended and then resumed.  The kernel's blacklist is growing 
rapidly, and some people are concluding that responsibility for all 
this should be moved to userspace.

In principle we could enable autosuspend for devices by default and 
rely on user tools to disable it for bad devices, but in reality this 
approach isn't workable.  At boot time especially, so many things 
happen at once that the kernel might suspend a device before the user 
tool could get a chance to tell it not to.

My feeling is that it would be best to leave autosuspend disabled by
default for all USB devices other than hubs, and have a user tool
enable it for devices where it's okay.  (Matthew Garrett suggested
something similar, but less far-reaching.)  The obvious candidate tool
is HAL.  There could be a database of devices which have been seen
before, or devices which the user has tested and knows to work okay
with autosuspend.  Included in this database could be the idle-time
delay for autosuspending.

Desktop GUIs could include a program to open a pop-up window when a 
new, unrecognized USB device is encountered, to ask whether autosuspend 
should be enabled.  They also could include simple ways for users to 
enable or disable it (and change the delay value) for individual 
devices.

What do you think?

Alan Stern


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