DCON Linux Driver
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