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SubjectRe: [linux-usb-devel] USB autosuspend and turning of usb pendrive leds
On Sat, 22 Sep 2007, Hans de Goede wrote:

> I'm afraid that that doesn't work for usb mass-storage devices.
>
> Here is what I did:
> 1) kill hal
> 2) insert usb stick -> led lights
> 3):
> echo -n 1 > /sys/bus/usb/devices/.../power/autosuspend
> echo -n auto > /sys/bus/usb/devices/.../power/level
>
> 4) wait
>
> Nothing happens, where as sending "suspend" to power/level does turn the led
> off.

I don't know what went wrong. It works fine on my systems. You did
fill in the correct device path for the "...", right? And you don't
need the "-n" -- adding it shouldn't matter, but you should try reading
back the contents of those files to make sure the values did get
written correctly.

> Now call me naive, but I would expect a mass-storage devices with no
> partitions mounted to autosuspend when autosuspend is enabled for that device.

Yes, that is naive. The driver has no way to tell whether or not any
partitions are mounted. Furthermore, you might very well want to
access the raw device without mounting any partitions (database
managers frequently do such things to reduce I/O overhead), in which
case you certainly would not the device to be autosuspended.

> And yes I'm pretty sure nothing else is talking to the device.

You can be absolutely certain by using usbmon (see
Documentation/usb/usbmon.txt). It will also show whether any suspends
or resumes are actually being sent.

Alan Stern

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