Dell distributes BIOS updates for the Latitude E7270 as PE32 Windows GUI executables. It turns out that the BIOS itself is able to extract the firmware images from such executables and to apply them.
- Get the latest BIOS update executable from e.g.
https://www.dell.com/support/home/de/de/debsdt1/product-support/servicetag/$YOURTAG/drivers. For example, as of 2017-02-06 this would be
- Verify the cryptographic file checksum (yes, Dell publishes them over https)
- Put the executable on a FAT formatted USB stick
- Reboot the machine and press F12 when the Dell logo is displayed
- Select the firmware upgrade menu entry
- Select the BIOS update executable in the file selection dialog and continue
USB Stick Partitioning¶
What does work:
- DOS-style partition table
- 1 primary partition
- bootable partition flag
- 0xe partition type (W95 FAT16 LBA)
- vfat filesystem
As always, Dell's documentation isn't very helpful. The BIOS install instructions just describe how to run the executable in a Windows or DOS environment. Which is scary if you are running Linux or something like that. They explicitly instruct 'Non-Windows users' to boot into DOS using a USB stick and to start the update executable from the DOS prompt. The more convenient alternative described above isn't mentioned in the Dell install instructions, at all.
The problem with USB-booting into DOS is that it is surprisingly tedious to get a proper ready-to-use USB FreeDOS image. Freedos.org only provides installer images. There is the seemingly popular Unetbootin GUI that supports creating a FreeDOS USB stick but it downloads the images as root and doesn't do any verification of the downloaded files, which both is quite irresponsible and dangerous. There are even some ready-to-use FreeDOS images available from private sites, but even if you trust the individuals, usually they don't provide any means for verification of the downloaded images (e.g. checksums over https, GPG generated file signatures).
As-is, using Christian Taube's FreeDOS image generation HOWTO is the best option one has to create a FreeDOS bootable USB stick.
The BIOS update executable actually contains multiple firmware images. That means that besides the traditional BIOS also the firmware of the embedded controller (EC) and of the Intel Management Engine (ME) is updated.