u-boot/doc/driver-model/UDM-tpm.txt

The U-Boot Driver Model Project
===============================
TPM system analysis
===================
Marek Vasut <marek.vasut@gmail.com>
2012-02-23

I) Overview
-----------

There is currently only one TPM chip driver available and therefore the API
controlling it is very much based on this. The API is very simple:

  int tis_open(void);
  int tis_close(void);
  int tis_sendrecv(const u8 *sendbuf, size_t send_size,
			 u8 *recvbuf, size_t *recv_len);

The command operating the TPM chip only provides operations to send and receive
bytes from the chip.

II) Approach
------------

The API can't be generalised too much considering there's only one TPM chip
supported. But it's a good idea to split the tis_sendrecv() function in two
functions. Therefore the new API will use register the TPM chip by calling:

  tpm_device_register(struct instance *i, const struct tpm_ops *ops);

And the struct tpm_ops will contain the following members:

  struct tpm_ops {
    int (*tpm_open)(struct instance *i);
    int (*tpm_close)(struct instance *i);
    int (*tpm_send)(const uint8_t *buf, const size_t size);
    int (*tpm_recv)(uint8_t *buf, size_t *size);
  };

The behaviour of "tpm_open()" and "tpm_close()" will basically copy the
behaviour of "tis_open()" and "tis_close()". The "tpm_send()" will be based on
the "tis_senddata()" and "tis_recv()" will be based on "tis_readresponse()".

III) Analysis of in-tree drivers
--------------------------------

There is only one in-tree driver present, the "drivers/tpm/generic_lpc_tpm.c",
which will be simply converted as outlined in previous chapter.