linux-kernel - Re: [PATCH 1/4] hid-multitouch: Auto detection of maxcontacts

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Message-ID: <20110309093809.GA3980@polaris.bitmath.org>
Date:	Wed, 9 Mar 2011 10:38:09 +0100
From:	"Henrik Rydberg" <rydberg@...omail.se>
To:	Benjamin Tissoires <benjamin.tissoires@...c.fr>
Cc:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Stephane Chatty <chatty@...-enac.fr>,
	linux-input@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] hid-multitouch: Auto detection of maxcontacts

On Wed, Mar 09, 2011 at 10:03:45AM +0100, Benjamin Tissoires wrote:
> On Wed, Mar 9, 2011 at 09:42, Henrik Rydberg <rydberg@...omail.se> wrote:
> > Hi Benjamin,
> >
> >> This patch enables support of autodetection of maxcontacts.
> >> We can still manually provide maxcontact in case the device
> >> lies on it.
> >>
> >> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...c.fr>
> >
> > It seems quite alright to let the classes contain the expected number
> > of contacts, so I do not really see the reason for that part of the
> > patch. How about keeping the maxcontacts in the class, and then do
> > max(hid-provided-maxcontacts, default-maxcontacts)?
> >
> 
> Yep, I've got three particular reasons:
> - 3M: there are two devices now, 1968 and 2256. The first one is a 10
> touches only, whereas the second one is a 60 touches.

Right, so increasing the number of touches based on device information
seems like a good idea.

> - autodetection of multitouch devices. I have some patches on my tree
> (that we do not want to go upstream right now for some reasons) that
> allows us to plug any unknown multitouch devices and to let
> hid-multitouch handling it. As most of the devices are 2 touches only,
> and as the generic way to work with a multitouch devices is to iterate
> over all the slots, using 10 touches by default infers a lot of
> instructions that can be avoided.

Right, so keeping the default number of touches per class seems like a
good idea.

> - finally, it simplifies the writing of the new CLS (we just need to
> know how the device works to add the right quirks).

Right, we always need to know how the device works. :-)

Cheers,
Henrik
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