linux-kernel - Re: [PATCH 2/6] Input: elantech - use firmware provided x, y ranges

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4E666D56.1020009@canonical.com>
Date:	Tue, 06 Sep 2011 11:58:30 -0700
From:	Chase Douglas <chase.douglas@...onical.com>
To:	Henrik Rydberg <rydberg@...omail.se>
CC:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	JJ Ding <jj_ding@....com.tw>, linux-input@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Seth Forshee <seth.forshee@...onical.com>,
	Aaron Huang <aaron_huang@....com.tw>,
	Tom Lin <tom_lin@....com.tw>,
	Eric Piel <E.A.B.Piel@...elft.nl>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Alessandro Rubini <rubini@...l.unipv.it>
Subject: Re: [PATCH 2/6] Input: elantech - use firmware provided x, y ranges

On 09/06/2011 11:47 AM, Henrik Rydberg wrote:
>>>> I see that the current code scales the coordinates for v2, but it's only
>>>> half-resolution. That's not a huge deal since the resolution of modern
>>>> touchpads is very high. We could leave it scaled to not break abi, if
>>>> that was a concern. However, with new devices it makes sense to state
>>>> the ranges in terms of what the device actually supports. Otherwise,
>>>> we're just masking out useful data that userspace could be using.
>>>>
>>>
>>> I disagree. I believe that ST and MT ranges reported for the same
>>> working surface should match, especially since many devices derive ST
>>> data from MT.
>>>
>>> As far as devices that have ranges 0-15 in MT mode - I am not sure how
>>> useful such MT steam anyway and if we are better of just ignore them
>>> (maybe just use the data to report number of fingers on the surface but
>>> otherwise use standard ST protocol).
>>
>> The MT data could still be useful for pinch to zoom or potentially
>> rotate (though most low res devices probably are only semi-mt). I don't
>> want to forsake pinch to zoom just because we can't pass on the
>> resolution of MT data properly.
> 
> We are not forsaking anything. At best, the detail missed out by using
> the same scaling for ST and MT is the ability to distinguish the axis
> with the best or poorest resolution. However, some devices report
> higher MT than ST resolution, not because it is better (it is indeed
> worse), but simply to not lose bits in the filtering process. In other
> words: the logic is not without corner cases, and it only makes a
> difference to the transitional devices that are not fully MT
> capable. If this really was a concern, userspace could use the ST
> coordinates for some transformations instead.

So what do we want userspace to do? In the absence of supplying this
information we need to provide guidelines. We could say:

* Always use ST coords + finger count for drag gestures (i.e. scrolling)
* Use MT coords for pinch and rotate

If this is acceptable, we should add it to the documentation. Thoughts?

-- Chase
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/