DCON Linux Driver

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This page describes the Linux kernel drivers for the DCON on the XO Laptop.

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:

Output	Value
Color	0
Mono	1

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:

Source	Value
DCON	0
CPU	1

Read the file to see what the current source is.

/sys/devices/platform/dcon/sleep

Allows you to put the DCON into sleep mode. To turn the display off, echo "1" > /sys/devices/platform/dcon/sleep

Using the backlight driver

/sys/class/backlight/dcon-bl looks like this:

actual_brightness  max_brightness     subsystem
brightness         power              uevent

Change the brightness by writing a new number to the brightness file. The value can range from 0 (off) to 15 (full on).

This example changes the backlight to about 50%:

$ echo "7" > /sys/class/backlight/dcon-bl/brightness

Using the DCON driver (ioctl)

The DCON functionality can also be accessed with ioctl() calls through the /dev/fb0 device file. The following ioctls are defined:

#define DCONIOC_SOURCE          _IOW('d', 0, int)
#define DCONIOC_OUTPUT          _IOW('d', 1, int)
#define DCONIOC_SETREG          _IOW('d', 2, int) 
#define DCONIOC_DUMPREG         _IOW('d', 3, int) 
#define DCONIOC_GETREG          _IOW('d', 4, int) 
#define DCONIOC_SETBL           _IOW('d', 5, int)
#define DCONIOC_GETBL           _IOW('d', 6, int)

DCONIOC_SOURCE

Change the source of the DCON data. The argument should either be 0 (DCON) or 1 (CPU).

DCONIOC_OUTPUT

Change the output type of the display. The argument should either be 0 (color) or 1 (mono).

DCONIOC_SETREG

Sets a register on the DCON. Upper 16 bits of the argument is the register, and the lower 16 bits is the value.

DCONIOC_DUMPREG

Prompts the driver to prink() all of the registers in the DCON.

DCONIOC_GETREG

Get a DCON register value. The argument is the desired register and it will contain the value on return.

DCONIOC_GETBL

Get the current value of the backlight register. The argument will contain the backlight value on return.

DCONIOC_SETBL

Set the current value of the backlight register. The argument should have the new value. Any value from 0 (off) to 15 (full on) is acceptable

Driver Installation

Warning: These instructions are relatively obsolete, and certainly not needed if you are using a Sugar, DebXO or Fedora build for the laptop!

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