DCON

DCON overview

DCON stands for Display CONtroller. As it says on the Hardware Specification page: The special "DCON" chip, that enables deswizzling and anti-aliasing in color mode, while enabling the display to remain live with the processor suspended. The following is a simple diagram detailing the various connections between the CPU and the DCON:

DCON Linux Driver

This section describes the Linux kernel drivers for the DCON and associated hardware.

Requirements

The latest and greatest DCON code is in the 'dcon' branch of the geode GIT tree: git://git.infradead.net/users/jcrouse/geode.git.

Make sure that you enable the following devices:

• The Geode GX frambuffer driver (CONFIG_FB_GEODE and CONFIG_FB_GEODE_GX). Make sure you build this into the kernel - its not useful as a module.
• The DCON driver (CONFIG_FB_GEODE_GX_DCON). You can either build this in to the kernel or use it as a module. Its much easier to debug as a module. This option automatically selects the I2C subsystem.
• The Geode ACB (smbus) driver (CONFIG_SCx200_ACB).
• The DCON backlight driver (CONFIG_BACKLIGHT_LCD_SUPPORT and CONFIG_BACKLIGHT_CLASS_DEVICE and CONFIG_BACKLIGHT_DCON). This module allows you to control the backlight through the existing kernel backlight mechanism.

Loading the DCON driver(s)

• Load the I2C driver (if you didn't build it in)

$ modprobe scx200_acb

• Load the DCON driver

$ modprobe gxfb_dcon

• Load the backlight driver

$ modprobe dcon_bl

The driver is now loaded. There should be two new platform drivers in /sys/devices/platform:

dcon        i2c-0       power       uevent
dcon-bl     pcspkr      serial8250

Using the DCON driver (/sys interface)

The DCON driver functionality is accessable through the /sys interface. This may not always be the case, since it might be a bit of a security issue, but its good for debugging. Here is what the /sys/devices/platform/dcon directory looks like:

bus        mode       power      source     uevent
modalias   output     sleep      subsystem

/sys/devices/platform/dcon/mode

This is a read only file that shows the current hex value of the DCON mode register (0x01).

/sys/devices/platform/dcon/output

This file lets you change the output mode from color to mono. Write a number to the file to change the mode:

0 = color

1 = mono

Read the file to see what the current mode is.

/sys/devices/platform/dcon/source

This file lets you change the source of the display from the CPU to the DCON. Write a number to the file to change the source:

0 = DCON

1 = CPU

Read the file to see what the current source is.

/sys/devices/platform/dcon/sleep

This file isn't yet implemented, but it will alow you to put the DCON into sleep mode.