[BRLTTY] brltty causes excessive resume of USB

[Dave Mielke]

[quoted lines by Samuel Thibault on 2008/08/30 at 12:21 +0100]

>We got a bug report in Debian (http://bugs.debian.org/497155):
...
>> During investigation of an issue with USB in the kernel [1] I found that 
>> the USB busses on my system were being activated from suspension way too 
>> often. Some debugging identified brltty as the culprit.

This has been resolved in 3.10 (maybe 3.9, but I'd have to check). If the 
kernel is recent enough (2.6.23?) then (thanks to Allan Stern who specifically 
listened to our concerns and also understood that commands like lsusb would 
beenfit from it) the USB device descriptor is available under /sys, and opening 
that special file doesn't resume the device. Brltty currently checks two paths 
for the it (<b> represents the bus number and <d> the device number):

   /sys/class/usb_device/usbdev<b>.<d>/device/descriptors
   /sys/class/usb_endpoint/usbdev<b>.<d>_ep00/device/descriptors 

There are kernel options which enable/disable some of these paths, though, so, 
even with the most recent kernel, it's possible that none of them is there. 
Also, it's entirely possible that there are other paths which I haven't 
discovered yet.

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