These are repositories containing the original 2005 PDF. While legally dubious to host, these are easy to find. Beware: If you try to compile the examples from this book on a modern Kernel (5.15+), they will fail spectacularly. The init_module and cleanup_module macros still work, but the struct file_operations has changed, and procfs no longer looks the same.
Go to GitHub and search for lwnlinux (LWN.net) or gregkh. Greg Kroah-Hartman (the Linux Foundation Fellow and co-author of the 3rd edition) maintains a repository called driver-api within the official Linux kernel documentation. Linux Device Drivers 4th Edition Pdf Github
Do not look for a PDF. Clone the kernel docs: These are repositories containing the original 2005 PDF
git clone https://github.com/torvalds/linux
cd linux/Documentation/driver-api/
Inside, you will find index.rst – this is the de facto 4th edition. It is updated every time Linus Torvalds merges a pull request. Inside, you will find index
The source code examples from the 3rd Edition are open source and hosted on GitHub. Searching for ldd3 yields the official repositories.