We can provide expertise is writing device drivers for Linux systems. This is not limited to embedded systems, but can be for any system running a linux kernel and operating system.
The usual way to write a driver is to take an existing driver for a similar device and amend it accordingly.
This is the approach we usually take as it is generally quicker to complete.
We can alo write the driver from scratch when required, although we always recommend starting with some form of 'skeleton' as a starting point.

One project that NB TechKnowledgy Ltd. worked on was was a 10 port gigabit router, created from a clean sheet, it was designed without trying to emulate or by copying a pre-existing device.
The hardware was designed by an external hardware consultant hired by the client.
The software was provided exclusively by NB TechKnowledgy Ltd. using an embedded linux solution.
The project required drivers to be written for the Marvell router silicon, and additional drivers need to be written to provide a 'hot-plug' solution for the plugin SFPs which could be interchanged with different types without having to power down, reboot, or even do any reconfiguring.
The driver notified the OS, and the newly inserted SFP came online without any operator intervention.

SFP -- a Small Form-factor Pluggable device to provide a network interface using either copper or fibre optic connections.

We have also written drivers for QNX operating system. They involved writing a driver to make the a Cisco PCMCIA WiFi device operate in a system running the QNX operating system.
Additionally, facilities were provided to allow over the air firmware updates of the Cisco device.