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

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Message-ID: <20121006220421.47f5fd56@endymion.delvare>
Date:	Sat, 6 Oct 2012 22:04:21 +0200
From:	Jean Delvare <khali@...ux-fr.org>
To:	"benjamin.tissoires" <benjamin.tissoires@...il.com>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Stephane Chatty <chatty@...c.fr>, fabien.andre@...il.com,
	scott.liu@....com.tw, Ben Dooks <ben-linux@...ff.org>,
	Wolfram Sang <w.sang@...gutronix.de>,
	linux-i2c@...r.kernel.org, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] i2c-hid: introduce HID over i2c specification
 implementation

Hi Benjamin,

On Fri, 14 Sep 2012 15:41:43 +0200, benjamin.tissoires wrote:
> From: Benjamin Tissoires <benjamin.tissoires@...c.fr>
> 
> Microsoft published the protocol specification of HID over i2c:
> http://msdn.microsoft.com/en-us/library/windows/hardware/hh852380.aspx
> 
> This patch introduces an implementation of this protocol.
> 
> This implementation does not includes the ACPI part of the specification.
> This will come when ACPI 5.0 devices will be available.
> 
> Once the ACPI part will be done, OEM will not have to declare HID over I2C
> devices in their platform specific driver.
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...c.fr>
> ---
> 
> Hi,
> 
> this is finally my first implementation of HID over I2C.
> 
> This has been tested on an Elan Microelectronics HID over I2C device, with
> a Samsung Exynos 4412 board.
> 
> Any comments are welcome.
> 
> Cheers,
> Benjamin
> 
>  drivers/i2c/Kconfig         |    8 +
>  drivers/i2c/Makefile        |    1 +
>  drivers/i2c/i2c-hid.c       | 1027 +++++++++++++++++++++++++++++++++++++++++++
>  include/linux/i2c/i2c-hid.h |   35 ++
>  4 files changed, 1071 insertions(+)
>  create mode 100644 drivers/i2c/i2c-hid.c
>  create mode 100644 include/linux/i2c/i2c-hid.h

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.

Also, you need to sort out dependencies. Your causes a link failure here:

ERROR: "hiddev_report_event" [drivers/i2c/i2c-hid.ko] undefined!
ERROR: "hiddev_disconnect" [drivers/i2c/i2c-hid.ko] undefined!
ERROR: "hiddev_connect" [drivers/i2c/i2c-hid.ko] undefined!
ERROR: "hid_pidff_init" [drivers/i2c/i2c-hid.ko] undefined!
make[1]: *** [__modpost] Erreur 1
make: *** [modules] Erreur 2

This is because these functions aren't exported and I tried to build
i2c-hid as a module.BTW I see that these functions are part of the
usbhid driver, which looks seriously wrong. If these functions are
transport layer-independent, they should be moved to the hid-code or
some sub-module. One should be able to enable HID-over-I2C without
HID-over-USB.

-- 
Jean Delvare
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