Re: [ddccontrol-devel] non root i2c communication

[Kai-Uwe B. <ku...@gm...>]

Hello,

Am 03.12.09, 12:46 +0100 schrieb William OLLIVIER:
> Le 01/12/2009 14:28, Kai-Uwe Behrmann a écrit :
>> I have monitor here, which supports reading and writing of internal LUTs
>> over a small monitor framework[1]. It accesses the montor over i2c
>> device nodes. That would be nice to integrate in my graphic card LUT
>> viewer[2].
>>
>> Unfortunedly i2c requires root access on my system. And my understanding
>> is that i2c is a security issue to open for normal users.
> I wasn't aware of that. Where did you get this information from?

Seeing that i2c is used for several hardware controls, I guessed that it 
is cruical to not let ordinary users change clock speed and similiar by 
default. On my distribution the /dev/i2c-xxx devices are owned by root 
with chmod 0440. This is controled on startup, and again I guess this is 
similiar on many Linux distributions.

>> How can my
>> application nevertheless get the curves. As well there is interesst
>> to do more with this monitor communication channel.
>>
>> Can this be achieved over DDC/CI as well? What would be needed to make it
>> non root read and writeable.
>>
> What ddccontrol allows you to do is read and write values that are
> stored in the monitor's internal chip, so that you can control
> parameters like Brightness, Contrast, color temp, etc. from you
> computer, just as you would with the buttons and OSD of your monitor.
>
> ddccontrol can use different low-level protocols to do that : for
> example, I can use i2c, or use my Nvidia graphics card driver's
> capabilities to communicate with my monitor.

The nvidia extensions regarding ddc/ci I have noticed. They are probably 
not a general i2c interface but only ddc/ci. So access through them might 
be restricted to monitor communication than the i2c device nodes.

> DDC/CI is a protocol that works on top of i2c, so as far as I can tell,
> you will still need to run ddccontrol as root to be able to communicate
> with your monitor.

Thanks for your confirmation.

> A while ago, I tried to make ddccontrol work at a user level, but I
> didn't manage. I'm the current maintainer of the project, but I'm quite
> busy right now. Maybe we could figure something out together, when we
> both have time.

On the Xorg list, I started a thread about that matter. I think ddc/ci
would be best integrated therein. Hopefully this opens for a general API 
that ddccontrol can migrate to as well. Having not to rely on root access 
is for UI tools essential in order to get generally accepted for desktop 
use.

kind regards
Kai-Uwe Behrmann
-- 
developing for colour management 
www.behrmann.name + www.oyranos.org