linux-kernel - Re: [PATCH 1/7 v3] HID: magicmouse: don't allow hidinput to initialize the device

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Message-ID: <4C7F6E26.2030301@gmail.com>
Date:	Thu, 02 Sep 2010 11:28:06 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Michael Poole <mdpoole@...ilus.org>
CC:	Chase Douglas <chase.douglas@...onical.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Henrik Rydberg <rydberg@...omail.se>,
	Tejun Heo <tj@...nel.org>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/7 v3] HID: magicmouse: don't allow hidinput to initialize
 the device

On 09/02/2010 01:57 AM, Michael Poole wrote:
> Jiri Slaby wrote:
>> This looks weird. Is there any past discussion about why you cannot use
>> hidinput and you have to do all the input bits yourself while cheating
>> this very weird way?
> 
> The Magic Mouse and Magic Trackpad do not publish HID descriptors for
> the multitouch reports.  Given the variable-length report packets --
> and especially the Magic Trackpad's new, mutant DOUBLE_REPORT_ID
> packets -- it would be non-trivial to write accurate descriptors that
> the HID core can use.  (Someone wrote a patch to try that a few months
> ago.  It ended up adding significantly more lines to hid-magicmouse.c
> than it removed, and it was not obvious to me that it got the Report
> Count fields correct.)

Ok, makes sense. The proper solution is to call a driver hook in
hidinput_connect to do the mapping instead of report parsing done there,
right? (And not setting [gs]etkeycode in that case.)

Then the part of magicmouse_setup_input starting at the first __set_bit
will be exactly the hook.

Otherwise this hack looks like a hard cross-layer breakage.

/me wonders how HID issuers are creative in breaking standards.

regards,
-- 
js
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