[RFC] TPM non-MMIO Access

["Cohen, Eugene" <eugene@hp.com>]

Dear SecurityPkg maintainers,

We are trying to use the SecurityPkg TPM support (Tcg2Config, Tpm2DeviceLibDTpm, etc) and see that access to the TPM are using the MMIO routines such as MmioRead8().

Not all platforms support memory-mapped access to the TPM so we would like to propose that we create a library to abstract the TPM access, called the TpmIoLib.  One instance of the library would provide the Mmio (TpmIoLibMmio) method but others can use protocols like SPI (TpmIoLibSpi).

Before starting this work I wanted to check if you agree with the approach of replacing the Mmio calls with new TpmIoLib ones.  We can upstream the library header and mmio library instance (or you could do the work if you think it would be easier for you).

I counted up the number of instances of unique MMIO calls in the TPM libraries and got

Library/TpmCommLib/TisPc.c:7
Library/Tpm2DeviceLibDTpm/Tpm2Tis.c:13
Library/Tpm2DeviceLibDTpm/Tpm2Ptp.c:29
Library/Tpm12DeviceLibDTpm/Tpm12Tis.c:16

Please let me know if this works for you and how you'd like to structure the change.

Thanks,

Eugene