Re: usb device removed from sysfs before input children devices

On Tue, 2013-01-15 at 20:27 +0000, Karl Relton wrote:

quoted

The end result (for the user) is that even when the bluetooth
mouse/keyboard is re-added, Xorg ignores it - thinking it is some

hoax

quoted

duplicate device. The keyboard/mouse is then non-operational.

Instrumenting the code suggests that the issue arises in a race
between:

hidp_session() in bluetooth/hidp/core.c

and

hci_unregister_dev() in bluetooth/hci_core.c


Basically hci_unregister_dev() does a hci_dev_do_close() which in turn
shuts down the hidp connection. This causes hidp_session() running in
another thread to go into its cleanup phase, which is where the input
children devices are unregistered.

HOWEVER:
1) For some reason input_unregister_device() seems to stall some 3-5
seconds on my system before removing the input device
2) In parallel hci_unregister_dev() ploughs on, and progresses to
remove
its hdev (hci<n> device) regardless, without waiting for
hidp_session()
to complete.

I can't figure out why there is such a delay for
input_unregister_device(). 

The power_supply system seems to be triggering a lookup of battery
'capacity' in the input device. This calls into the driver, which deep
down invokes more code in the 'hidp' module: hidp_get_raw_report()

This function tries to communicate with the bluetooth device (keyboard
in my case), but because the device is being 'torn down' such
communication fails. Accordingly hidp_get_raw_report has a 5 second
timeout ... so this function stalls for 5 seconds until that timeout
occurs.


I would guess that for some reason, removing the 'hid' or associated
'input' device is leading to the power_supply code wanting to lookup the
battery capacity which introduces a 5 second wait. This would delay
hidp_session by 5 seconds ... in the mean time allowing
hci_unregister_dev() to win the race and hence the hci device is removed
before the input & hid devices.