linux-kernel - HID: questions about polling rates

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Date:	Fri, 12 Nov 2010 20:15:52 +0100
From:	Stefan Achatz <erazor_de@...rs.sourceforge.net>
To:	Jiri Kosina <jkosina@...e.cz>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: HID: questions about polling rates

Hello,

while working on my roccat device drivers I thought about the possiblity
of on the fly polling rate changes and tested some things.

First I tried different polling rates by writing values from 1 to 10
into /sys/bus/usb/drivers/usbhid/module/parameters/mousepoll. I observed
that the polling rates seem to be capped on both sides. With value 1 I
measure 2ms instead of 1ms with my hardware protocol analyzer. With 10 I
get 8ms instead of 10ms.
I only use cheap onboard usb controllers, but under windows they work
with 1ms.
A internet and code search revealed nothing regarding this to me. Is
someone of you aware of this behaviour and could tell me more about it?

Changing the polling rate of a device on the fly would requires to use
usb_kill_urb() and usb_submit_urb() with new interval. To get the
int_urb I would need additional informations for incomplete struct
usbhid_device that lie in drivers/hid/usbhid/usbhid.h.
My driver code is at home in drivers/hid/. Is it okay to include a
header further down in the structure? Or does anyone have concerns about
moving the mentioned header to include/linux? Is this a matter to follow
at all?

Thanks in advance
Stefan

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