LVDS and DP through i2c

Kai-Uwe Behrmann ku.b at
Mon Dec 27 22:51:21 PST 2010

Am 28.12.10, 16:16 +1100 schrieb Graeme Gill:
> Alex Deucher wrote:
>> i2c bit algo hooks.  Next, make sure you are opening the correct i2c
>> bus.   On radeons, we expose all of the on board i2c buses.  In most
>> cases, each connector uses a different i2c bus and there are
> If it's all too hard to actually put the i2c interface into the XRandR I/F,
> how about at least making sure that the display i2c device name is set as
> an output property ? That way there wouldn't need to be any guessing,
> or require some user action for software to talk to the display associated
> with a particular output. The property name needs to be standardised too,
> "OUTPUT_I2C_DEVICE_NAME", or something.

Do you have any special reason to put the "OUTPUT" part in front?
Otherwise I doubtless agree. Such a property would be very helpful. See 
as well the according thread from summer [1].

> [And what are the permissions on the i2c device ? Does the user have
> to jump through hoops for the application to actually do I/O ? If so,
> is there a means to add the display output i2c device to udev ? ]

The plan for libXcm includes as well the udev rules and permissions for 
normal user side applications. A daemon for EEDID fetching with root 
privilegs is not nice. ArgyllCMS can then require the appropriate Xcm sub
package and will be able to communicate without root rights. libXcm has 
not other dependencies than Xorg.

kind regards
Kai-Uwe Behrmann
developing for colour management +


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