Entropy estimation by Linux Kernel when adding entropy from TRNG
When you are adding entropy from outside the kernel, the kernel's entropy estimation functions are not used. Instead the entropy count is either not updated (e.g. if you just write data to /dev/random) or is updated according to the entropy count given to the kernel (e.g. through the RNDADDENTROPY ioctl).

Since you are using rngd, it will run some tests and assuming they pass ask the kernel to credit the entropy count with the full size of the data that was mixed in. I.e. 160 bits if you had 160 bits of data from the TRNG.