[U-Boot] tpm / measured boot in u-boot

I saw Simon's write-up here: https://lwn.net/Articles/571031/, which references TPM and trusted boot support using the TPM.

I've started looking at the TPM support code in u-boot, and am trying to understand it. Before getting too far I wanted to check if there were any pointers anyone might have around any documentation or material that provides more detail on what the u-boot TPM support does and does not do. I didn't see any .txt files in u-boot.

The supports seems oriented around using commands and scripts to measure images. One specific thing I'm interested is how the u-boot script itself that takes the TPM measurements is protected against tampering.

Also, it doesn't look like TCG compliant event logs are supported.

Thanks, Stuart