linux-kernel - Re: [PATCH 4/5] HID: autoload hid-multitouch as needed

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Date:	Tue, 13 Mar 2012 11:17:38 +0100
From:	Stéphane Chatty <chatty@...c.fr>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Marcel Holtmann <marcel@...tmann.org>,
	Henrik Rydberg <rydberg@...omail.se>,
	"benjamin.tissoires" <benjamin.tissoires@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Gustavo F. Padovan" <padovan@...fusion.mobi>,
	linux-bluetooth@...r.kernel.org
Subject: Re: [PATCH 4/5] HID: autoload hid-multitouch as needed


Le 12 mars 2012 à 23:21, Jiri Kosina a écrit :

> On Mon, 12 Mar 2012, Stéphane Chatty wrote:
> 
>> Just in case it makes a difference, I knew nothing about HIDP when I 
>> wrote the message above. My point was rather that hid looks like a bus 
>> to which several transport layers can connect (USB, Bluetooth, ZigBee, 
>> etc), and that having USB-specific code in hid/ (as opposed to having it 
>> in usb/) seems biased towards USB. I was (and am still) wondering how 
>> much it limits future uses of the hid core by making it USB-dependent.
>> 
>> In other words: is the hid core generic enough or are there steps to 
>> take to make it more generic wrt transport layers? If we are talking 
>> about restructuring parts of it, this seems like the right time to ask 
>> :-)
> 
> Let me answer by a bit of history here. Originally, there have been two 
> copies of HID code in the kernel -- one for USB HID devices, one for 
> Bluetooth HID devices.
> The parsers were not kept in sync, and there was a lot of code 
> duplication, creating quite some mess.
> 
> What I did back then in 2006 was that I have extracted the abstract HID 
> parts into HID core, and made it transport-independent in principle, so 
> that both USB HID and Bluetooth HID shared the common infrastructure, 
> while implementing different transport protocols.
> 
> Then we extended it a little bit further, making HID core a proper bus, to 
> which individual drivers (independently on underlying transport protocol 
> used) can register.
> 
> Currently there are just Bluetooth (hidp) and USB (usbhid) transport 
> implementations, with HID core being transport independent.
> 
> Hope this helps,

Very useful clarification, thanks. Now, I guess I understand why Marcel wants to keep hidp in bluetooth/. And, to be honest, things would have been clearer to me when I explored the handling of the USB/HID class if I had found a hid (or usbhid) directory in usb/ rather than a usbhid subdirectory in hid/: it did not make the above situation very obvious to me. Don't you think we could go along with Marcel and move usbhid to usb/?

St.




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