[TF-A] Measured boot and external TPM modules

Hi, I'm currently working on porting TFA to our upcoming SOC. We plan to support Measured boot using external I2C TPM module. I'm wondering about the implementation of that in BL1. Do you think that I need to write the measurements directly to the I2C module in BL1 ? I'm asking because I would like to have the least source of problems in BL1 which I can't upgrade. I thought of storing the measurements in secure RAM and perhaps copy later. Would love to hear your thoughts.

PS. Actually I would love to have the option to choose to implement TPM also in SW (fTPM using optee - as was done in the POC). I think that if I store the measurement of BL2 in secure RAM I can later change the specific TPM while upgrading only BL2/BL31...

Thanks, Ramon