linux-kernel - Re: [PATCH v1] i2c-hid: introduce HID over i2c specification implementation

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Message-Id: <3289FFF0-9B90-4F2D-8ECA-EE344911FBC0@enac.fr>
Date:	Sat, 6 Oct 2012 23:27:47 +0200
From:	Stéphane Chatty <chatty@...c.fr>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	"benjamin.tissoires" <benjamin.tissoires@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Fabien André <fabien.andre@...il.com>,
	劉嘉駿 <scott.liu@....com.tw>,
	Ben Dooks <ben-linux@...ff.org>,
	Wolfram Sang <w.sang@...gutronix.de>,
	linux-i2c@...r.kernel.org, USB list <linux-input@...r.kernel.org>,
	linux-kernel@...r.kernel.org, Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [PATCH v1] i2c-hid: introduce HID over i2c specification   implementation


Le 6 oct. 2012 à 23:11, Jean Delvare a écrit :

> On Sat, 6 Oct 2012 22:30:00 +0200, Stéphane Chatty wrote:
>> Le 6 oct. 2012 à 22:04, Jean Delvare a écrit :
>>> Looks like the wrong place for this driver. HID-over-USB support lives
>>> under drivers/hid, so your driver should go there as well. Not only
>>> this will be more consistent, but it also makes more sense: your driver
>>> is a user, not an implementer, of the I2C layer, so it doesn't belong
>>> to drivers/i2c.
>> 
>> This is a question I asked a few months back, but apparently not all points of views had been expressed at the time. Currently, HID-over-USB lives in drivers/hid, but HID-over-BT lives in drivers/bluetooth. When I asked, Jiri explained that he maintained HID-over-USB and Marcel maintained HID-over-BT, which explained the choices made. Let's try to summarize what we know now:
>> 
>> The question is what drives the choice of where to put HID-over-XXX, among the following
>> 1- who the maintainer is. Here, Benjamin will probably maintain this so it does not help.
>> 2- dependencies. HID-over-XXX depends on HID as much as it depends on XXX, so it does not help.
>> 3- data flow. Indeed, HID is a client of HID-over-XXX which is a client of XXX. Are there other parts of the kernel where this drives the choice of where YYY-over-XXX lives?
>> 
>> Jiri, Marcel, Greg, others, any opinions?
> 
> My vote is a clear 3. It took me a few years to kick all users (as
> opposed to implementers) of i2c from drivers/i2c and finding them a
> proper home, I'm not going to accept new intruders. Grouping drivers
> according to what they implement makes it a lot easier to share code
> and ideas between related drivers. If you want to convince yourself,
> just imagine the mess it would be if all drivers for PCI devices lived
> under drivers/pci.


Having no strong opinion myself, I'm trying to get to the bottom of this :-) Here, I see two points that need clarification:

- I'm under the impression that the situation is exactly opposite between i2c and USB: drivers/usb contains lots of drivers for specific devices, but HID-over-USB is in drivers/hid. I actually found this disturbing when reading the HID code for the first time. Mmmm.
- given your explanation, I'd say that you would agree to 2 as well, if it meant for instance that HID-over-I2C is neither in drivers/hid nor drivers/i2c. Actually, you don't care whether it is 1, 2, or 3 that drives the choice as long as HID-over-I2C is not in drivers/i2c, do you? :-)

Cheers,

St.--
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