Re: autosuspend for HID devices, take #4

On Wed, 23 May 2007, Alan Stern wrote:

> I suspect it is keyboard-dependent.  For example, the keyboard's 
> internal buffer might be able to hold no more than one event, because 
> the designers expected the host to poll frequently.  Since the polling 
> can't occur during the wakeup interval, multiple events from that time 
> will get lost.

Hi Alan,

in such situation, I'd however expect the first N events to be lost, but 
the last events to arrive without problem.

What I am experiencing, however, is that the missing events are usually 
"the middle" ones.

I have in the meantime tested with another USB keyboard on the same 
system, still the very same behavior with lost keypresses. I will try the 
same keyboards on another system now, to verify whether it could be a USB 
hub's fault instead.

> It wouldn't be surprising to find lots of USB HID devices suffering from 
> this kind of problem.

Which unfortunately would render suspending them quite impossible, as 
losing keypresses this often is a big no-no :(

I will work on this a little bit more.

Thanks,

-- 
Jiri Kosina
SUSE Labs

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