What are DPDDC-B/C i2c devices?

Question

The output of i2cdetect -l (after modprobe i2c-dev) is:

i2c-0 i2c       i915 gmbus ssc                       I2C adapter  
i2c-1 i2c       i915 gmbus vga                       I2C adapter  
i2c-2 i2c       i915 gmbus panel                     I2C adapter  
i2c-3 i2c       i915 gmbus dpc                       I2C adapter  
i2c-4 i2c       i915 gmbus dpb                       I2C adapter  
i2c-5 i2c       i915 gmbus dpd                       I2C adapter  
i2c-6 i2c       DPDDC-B                              I2C adapter  
i2c-7 i2c       DPDDC-C                              I2C adapter     

I am curious as to what the i915 gmbus devices are, but really would like to know what the DPDDC-B and C are.

Answer 1

On my machine, i915 gmbus dpb refers to my DVI-connected monitor. i915 is the Intel graphics module.

The Display Data Channel (DDC) runs on the I²C bus and is mainly used to transmit Extended Display Identification Data (EDID) information from the display to the computer. EDID information describes the display's capabilities such as what resolutions it supports.

Running ddcutil detect will let you know if any DDC-enabled displays are connected.

And in monitors that support it, DDC/CI (Command Interface) can be used to control settings such as brightness/contrast/color/volume/input/etc. without having to use the OSD menu. ddcutil capabilities will let you know what DDC/CI capabilities your monitor supports, if any.

Answer 2

Do you have a DisplayPort connection by chance? I believe the DPDDC* are related.

The "i915 gmbus vga" is because, VGA now contains I2C for "DDC Serial Data Line" and "DDC Data Clock Line"

http://pinouts.ru/Video/VGAVesaDdc_pinout.shtml

Also more information, UEFI may play a role, https://communities.intel.com/message/254056

Here are three of my devices, all Intel. i2cdetect -l

Intel Atom Z530

i2c-0   i2c         gma500 gmbus disabled               I2C adapter
i2c-1   i2c         gma500 gmbus ssc                    I2C adapter
i2c-2   i2c         gma500 GPIOB                        I2C adapter
i2c-3   i2c         gma500 gmbus vga                    I2C adapter
i2c-4   i2c         gma500 GPIOA                        I2C adapter
i2c-5   i2c         gma500 gmbus panel                  I2C adapter
i2c-6   i2c         gma500 GPIOC                        I2C adapter
i2c-7   i2c         gma500 gmbus dpc                    I2C adapter
i2c-8   i2c         gma500 GPIOD                        I2C adapter
i2c-9   i2c         gma500 gmbus dpb                    I2C adapter
i2c-10  i2c         gma500 GPIOE                        I2C adapter
i2c-11  i2c         gma500 gmbus reserved               I2C adapter
i2c-12  i2c         gma500 gmbus dpd                    I2C adapter
i2c-13  i2c         gma500 GPIOF                        I2C adapter
i2c-14  i2c         intel drm LVDSBLC_B                 I2C adapter
i2c-15  i2c         intel drm LVDSDDC_C                 I2C adapter
i2c-16  smbus       SMBus SCH adapter at 0500           SMBus adapter 

i2c-16 is my DDR2 ram (decode-dimms), other devices don't have I2C connected DDR3 sadly.

Intel Atom E3825

i2c-0   i2c         i915 gmbus ssc                      I2C adapter
i2c-1   i2c         i915 gmbus vga                      I2C adapter
i2c-2   i2c         i915 gmbus panel                    I2C adapter
i2c-3   i2c         i915 gmbus dpc                      I2C adapter
i2c-4   i2c         i915 gmbus dpb                      I2C adapter
i2c-5   i2c         i915 gmbus dpd                      I2C adapter
i2c-6   i2c         DPDDC-B                             I2C adapter
i2c-7   i2c         DPDDC-C                             I2C adapter

Intel i7-4770R

i2c-0   i2c         i915 gmbus ssc                      I2C adapter
i2c-1   i2c         i915 gmbus vga                      I2C adapter
i2c-2   i2c         i915 gmbus panel                    I2C adapter
i2c-3   i2c         i915 gmbus dpc                      I2C adapter
i2c-4   i2c         i915 gmbus dpb                      I2C adapter
i2c-5   i2c         i915 gmbus dpd                      I2C adapter
i2c-6   i2c         DPDDC-C                             I2C adapter