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VGA/DVI/HDMI ports have an I2C interface (though DP tunnels I2C over AUX), which is normally used to read EDID information from monitors and control brightness,

VGA/DVI/HDMI ports have an I2C interface (though DP tunnels I2C over AUX), which is normally used to read EDID information from monitors and control brightness, but on Linux (not Windows) you can control it as a general-purpose I2C bus, dump and even rewrite EEPROMs placed on the monitor bus. In theory you could even hook up a Nunchuk or Classic Controller to a display output (with level shifters if you want to run the Nunchuk at 5V off a 3.3V bus), and write a Linux driver to communicate with the peripheral and expose it as a game controller.

duskwuff 2y ago
I2C is also extremely common as a low-speed peripheral bus in electronic devices - some common applications are: - Small EEPROMs, often used for configuration data or small firmware blobs - MEMS sensors (accelerometers, gyroscopes, etc) - Small LCD/OLED displays (e.g. 128x64) - Configuration ports on devices which use other busses for bulk data (e.g. display drivers, audio codecs, etc).
mmastrac 2y ago
The I2C part is something of an implementation detail -- it's only _really_ guaranteed to work as an EEPROM interface. It's usable on a lot of platforms, but again, not a guarantee.
crote 2y ago
You can even use the I2C bus to attach a second (tiny) display, see for example https://www.youtube.com/watch?v=8UbVgUFfN8U https://www.youtube.com/watch?v=8UbVgUFfN8U
extraduder_ire 2y ago
I use ddcutil all the time on linux to set my monitor brightness without needing to fiddle with the OSD.
- pabs3 2y ago
  The ddcutil folks also have a great GUI btw: https://www.ddcutil.com/#ddcui https://www.ddcutil.com/#ddcui Also, if you have ddcci-driver-linux installed, then the KDE desktop lets you adjust monitor brightness from the UI. Eventually Linux upstream might get the same functionality as the out-of-tree module. https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux
  - nyanpasu64 2y ago
    In my experience the KDE desktop lets you set monitor brightness from the UI... and on Wayland it happens even if you don't ask it to (https://bugs.kde.org/show_bug.cgi?id=494497 https://bugs.kde.org/show_bug.cgi?id=494497). You can turn it off by "setting the `POWERDEVIL_NO_DDCUTIL=1` environment variable in PowerDevil as described in its README file: https://invent.kde.org/plasma/powerdevil/-/blob/master/README.md#troubleshooting--reporting-bugs https://invent.kde.org/plasma/powerdevil/-/blob/master/READM..."
    - Am4TIfIsER0ppos 2y ago
      And here I was assuming it was changing to intel arc or display port (due to the card) or wayland (due to the driver) that causes my screens to jump to 100% brightness after they turn off. I see it still isn't fixed after 5 months so if I can't go back to X after my next update I'm putting my old nvidia back in.
      - nyanpasu64 2y ago
        I'd recommend following the steps at https://invent.kde.org/plasma/powerdevil/-/blob/master/README.md#troubleshooting--reporting-bugs https://invent.kde.org/plasma/powerdevil/-/blob/master/READM... to disable brightness control. You can switch to X11 too, but for some reason I get screen tearing and blocky incomplete updates I haven't looked for a workaround yet. systemctl --user edit plasma-powerdevil.service [Service] Environment="POWERDEVIL_NO_DDCUTIL=1" EDIT: I tried switching to Wayland on Arc and am getting stuttery mouse cursor movement at around 36 FPS. I wonder what's wrong...
atoav 2y ago
HDMI is an absolutely unhinged standard. I run the mediatec department at a university and the amount of things that can go wrong with HDMI is absolutely astonishing, when 99,9% of people at best what the digital equivalent of analog video /audio connections. The best thing was certain macbooks not working at a certain input. It the turns out HDCP was at fault, which is basically DRM for HDMI.

duskwuff 2y ago

I2C is also extremely common as a low-speed peripheral bus in electronic devices - some common applications are: - Small EEPROMs, often used for configuration data or small firmware blobs - MEMS sensors (accelerometers, gyroscopes, etc) - Small LCD/OLED displays (e.g. 128x64) - Configuration ports on devices which use other busses for bulk data (e.g. display drivers, audio codecs, etc).

mmastrac 2y ago

The I2C part is something of an implementation detail -- it's only _really_ guaranteed to work as an EEPROM interface. It's usable on a lot of platforms, but again, not a guarantee.

crote 2y ago

You can even use the I2C bus to attach a second (tiny) display, see for example https://www.youtube.com/watch?v=8UbVgUFfN8U https://www.youtube.com/watch?v=8UbVgUFfN8U

extraduder_ire 2y ago

I use ddcutil all the time on linux to set my monitor brightness without needing to fiddle with the OSD.

pabs3 2y ago
The ddcutil folks also have a great GUI btw: https://www.ddcutil.com/#ddcui https://www.ddcutil.com/#ddcui Also, if you have ddcci-driver-linux installed, then the KDE desktop lets you adjust monitor brightness from the UI. Eventually Linux upstream might get the same functionality as the out-of-tree module. https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux https://gitlab.com/ddcci-driver-linux/ddcci-driver-linux
- nyanpasu64 2y ago
  In my experience the KDE desktop lets you set monitor brightness from the UI... and on Wayland it happens even if you don't ask it to (https://bugs.kde.org/show_bug.cgi?id=494497 https://bugs.kde.org/show_bug.cgi?id=494497). You can turn it off by "setting the `POWERDEVIL_NO_DDCUTIL=1` environment variable in PowerDevil as described in its README file: https://invent.kde.org/plasma/powerdevil/-/blob/master/README.md#troubleshooting--reporting-bugs https://invent.kde.org/plasma/powerdevil/-/blob/master/READM..."
  - Am4TIfIsER0ppos 2y ago
    And here I was assuming it was changing to intel arc or display port (due to the card) or wayland (due to the driver) that causes my screens to jump to 100% brightness after they turn off. I see it still isn't fixed after 5 months so if I can't go back to X after my next update I'm putting my old nvidia back in.
    - nyanpasu64 2y ago
      I'd recommend following the steps at https://invent.kde.org/plasma/powerdevil/-/blob/master/README.md#troubleshooting--reporting-bugs https://invent.kde.org/plasma/powerdevil/-/blob/master/READM... to disable brightness control. You can switch to X11 too, but for some reason I get screen tearing and blocky incomplete updates I haven't looked for a workaround yet. systemctl --user edit plasma-powerdevil.service [Service] Environment="POWERDEVIL_NO_DDCUTIL=1" EDIT: I tried switching to Wayland on Arc and am getting stuttery mouse cursor movement at around 36 FPS. I wonder what's wrong...

atoav 2y ago

HDMI is an absolutely unhinged standard. I run the mediatec department at a university and the amount of things that can go wrong with HDMI is absolutely astonishing, when 99,9% of people at best what the digital equivalent of analog video /audio connections. The best thing was certain macbooks not working at a certain input. It the turns out HDCP was at fault, which is basically DRM for HDMI.