From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alan Ott Subject: Re: [PATCH 0/1] HID: Report Descriptor in Sysfs Date: Fri, 21 Jan 2011 10:29:36 -0500 Message-ID: <4D39A660.7040302@signal11.us> References: <1295590785-7101-1-git-send-email-alan@signal11.us> <4D399DAB.3080808@signal11.us> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from core.signal11.us ([64.251.29.136]:41052 "EHLO core.signal11.us" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752647Ab1AUQI7 (ORCPT ); Fri, 21 Jan 2011 11:08:59 -0500 Received: from localhost (localhost.localdomain [127.0.0.1]) by core.signal11.us (Postfix) with SMTP id A792E1CCABA7 for ; Fri, 21 Jan 2011 11:08:58 -0500 (EST) In-Reply-To: Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Jiri Kosina Cc: linux-input@vger.kernel.org, linux-kernel@vger.kernel.org On 01/21/2011 10:09 AM, Jiri Kosina wrote: > On Fri, 21 Jan 2011, Alan Ott wrote: > > >> Maybe it is. To be honest I didn't check debugfs. I have two concerns about >> it: >> 1. Is it wise for userspace programs to rely on: >> > Ah, I didn't realize that you want it to be used by some acutal userspace > applications. Out of curiosity -- what is the usage pattern you are > targetting? > Well, what I really want is the Usage Page and Usage of the device. For some background, I maintain a library called hidapi[1] for accessing HID devices in a cross platform way. There are currently four backends, Linux-hidraw, Linux-libusb, Mac OS, and Windows. I've recently received requests for supporting composite HID devices. Since a composite device will show up as multiple devices with the same VID/PID, one needs a way to differentiate between its different interfaces. On Windows and Mac, the platform HID libraries support getting the Usage Page and Usage of each interface. On Linux/libusb I can request the HID report descriptor and parse it myself, but I have to claim the interface to do it, and to do that, I have to detach the kernel driver. Needless to say, detaching the kernel driver is not good, especially when the library is supposed to be just scanning for devices. For these reasons, it would be really convenient to get the report descriptor from sysfs. Alan. [1] http://www.signal11.us/oss/hidapi/