From Gentoo Linux Wiki

[edit] SMBIOS Method

• First add kernel support:

Processor type and features  --->
    Firmware Drivers  --->
        <M> BIOS update support for DELL systems via sysfs
        <M> Dell Systems Management Base Driver

• To see, if your motherboard or notebook is supported by this method, install libsmbios:

# emerge -av libsmbios

• Then find your System ID:

# modprobe dcdbas
# getSystemId 

Libsmbios:    0.12.1
System ID:    0x01DD
Service Tag:  DT6WLB1
Express Service Code: 30063287773
Product Name: Dell DM061
BIOS Version: 2.3.2
Vendor:       Dell Inc.
Is Dell:      1

• Go to Dell and look out for your system. You have to find the entry following this schema:

system_bios_ven_0x1028_dev_SYSTEM_ID_version_BIOS_VERSION

If there is a folder like that and there is newer bios version, download the .hdr file.

• Alternatively one can extract the hdr image from the Windows BIOS upgrade utility by running it with -writehdrfile option. For example the following produces BIOS image in XPS420-A06.hdr file:

wine XPS420-A06.EXE -writehdrfile -nopause

• Upgrade your bios:

# modprobe dell_rbu
# dellBiosUpdate -u -f /path/to/file/bios.hdr

Supported RBU type for this system: (MONOLITHIC)
Using RBU v2 driver. Initializing Driver. 
Setting RBU type in v2 driver to: MONOLITHIC
Prep driver for data load.
Writing RBU data (4096bytes/dot): ............................
..............................................................
.......................
Notify driver data is finished.
Activate CMOS bit to notify BIOS that update is ready on next boot.
Update staged sucessfully. BIOS update will occur on next reboot.

• Finally, reboot the system. Make sure your battery is installed and your AC adapter is connected.
• If the BIOS complains of an incorrect checksum and fails, run the dellBiosUpdate tool again and see whether it's using "packet" updating, or "monolithic". If it's the former, you can try forcing it to use the latter via --force_mono, which may help things.

[edit] Biosdisk Method

• Install biosdisk:

# emerge -a biosdisk

• Then get the new bios from Dell. The file is called something like "D630_A02.EXE"
• Create a boot image:

# biosdisk install /path/to/file/D630_A02.EXE

This also copy the image to /boot and update your boot loader:

 ...
 title D630_A02.img
 root (hd0,0)
 kernel /memdisk
 initrd /D630_A02.img
 ...
 

• Copy memdisk of the syslinux package to /boot:

# cp /usr/lib/syslinux/memdisk /boot

• You should now reboot your laptop, select the new entry and follow the instructions on screen.
• After your bios has been successfully updated, boot your Gentoo and use the biosdisk uninstall command to remove the image and clean up grub.conf:

# biosdisk --uninstall /path/to/file/D630_A02.EXE

[edit] Links

• libsmbios
• Biosdisk
• Dell Wiki - smbios method