[linux-usb-devel] USB autosuspend and turning of usb pendrive leds

[linux-usb-devel] USB autosuspend and turning of usb pendrive leds

Post by Alan Ster » Sat, 22 Sep 2007 23:40:12



The correct answer is that HAL should top polling while the device is
suspended.

In kernels starting with 2.6.23-rc6, the correct way to enable
autosuspend for a USB device is basically like this:

echo D >/sys/bus/usb/devices/.../power/autosuspend
echo auto >/sys/bus/usb/devices/.../power/level

where D is the time (in seconds) the device should remain idle before
it is autosuspended. An autosuspended device will be woken up to
respond to polls. (Note however that in this kernel, autosuspend
support for USB mass-storage devices was removed because it can
cause problems related to spinning down disk drives.)

If instead you do

echo suspend >/sys/bus/usb/devices/.../power/level

it will simply suspend the device immediately. The device will not be
woken up automatically and attempts to poll it (or do anything else)
will fail.

Alan Stern

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[linux-usb-devel] USB autosuspend and turning of usb pendrive leds

Post by Hans de Go » Sun, 23 Sep 2007 23:20:07


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. 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.

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

As usual keep please me CC-ed as I'm not on the list.

Regards,

Hans
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[linux-usb-devel] USB autosuspend and turning of usb pendrive leds

Post by Alan Ster » Sun, 23 Sep 2007 23:30:14


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.


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.


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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[linux-usb-devel] USB autosuspend and turning of usb pendrive leds

Post by Hans de Go » Mon, 24 Sep 2007 02:20:08


Yes, the one that comes and goes as I plug in one of the USB-sticks I ue for
testing.


I did read them back and it did get written correctly.


How does this relate to your "It works fine on my systems" remark, do I need to
do anything other the unmounting the paritions to make the device eligible for
autosuspend, like unbind the sd driver or even the usb-storage driver?

If so I must say I find that a little counter intuitive.

Regards,

Hans


p.s.

As always, please keep me CC-ed, not on the list.

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[linux-usb-devel] USB autosuspend and turning of usb pendrive leds

Post by Alan Ster » Mon, 24 Sep 2007 05:20:09


You shouldn't have to do anything. Mounted or unmounted, bound to sd
or not bound, it shouldn't matter. Provided the device isn't being
used, it ought to autosuspend.

I repeat: To find out what is really happening, you should use usbmon.

Alan Stern

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