Quoting Stefan Berger (stef...@linux.vnet.ibm.com):
> This patch adds the main code of the TPM frontend driver, the TPM TIS
> interface, to Qemu. The code is largely based on my previous implementation
> for Xen but has been significantly extended to meet the standard's
> requirements, such as the support for changing of localities and all the
> functionality of the available flags.
>
> Communication with the backend (i.e., for Xen or the libtpms-based one)
> is cleanly separated through an interface which the backend driver needs
> to implement.
>
> The TPM TIS driver's backend was previously chosen in the code added
> to arch_init. The frontend holds a pointer to the chosen backend (interface).
>
> Communication with the backend is largely based on signals and conditions.
> Whenever the frontend has collected a complete packet, it will signal
> the backend, which then starts processing the command. Once the result
> has been returned, the backend invokes a callback function
> (tis_tpm_receive_cb()).
>
> The one tricky part is support for VM suspend while the TPM is processing
> a command. In this case the frontend driver is waiting for the backend
> to return the result of the last command before shutting down. It waits
> on a condition for a signal from the backend, which is delivered in
> tis_tpm_receive_cb().
>
> Testing the proper functioning of the different flags and localities
> cannot be done from user space when running in Linux for example, since
> access to the address space of the TPM TIS interface is not possible. Also
> the Linux driver itself does not exercise all functionality. So, for
> testing there is a fairly extensive test suite as part of the SeaBIOS patches
> since from within the BIOS one can have full access to all the TPM's
> registers.
>
> v3:
> - prefixing functions with tis_
> - added a function to the backend interface 'early_startup_tpm' that
> allows to detect the presence of the block storage and gracefully fails
> Qemu if it's not available. This works with migration using shared
> storage but doesn't support migration with block storage migration.
> For encyrypted QCoW2 and in case of a snapshot resue the late_startup_tpm
> interface function is called
>
> Signed-off-by: Stefan Berger <stef...@linux.vnet.ibm.com>
Most of this is pretty foreign to me so this doesn't mean much, but
Acked-by: Serge Hallyn <serge.hal...@ubuntu.com>
> +/*
Worth pointing out here that this is called with mutex held.
> + * read a byte of response data
> + */
> +static uint32_t tis_data_read(TPMState *s, uint8_t locty)
> +{
> + uint32_t ret = TPM_NO_DATA_BYTE;
> + uint16_t len;
> +
> + if ((s->loc[locty].sts & STS_DATA_AVAILABLE)) {
> + len = tis_get_size_from_buffer(&s->loc[locty].r_buffer);
> +
> + ret = s->loc[locty].r_buffer.buffer[s->loc[locty].r_offset++];
> + if (s->loc[locty].r_offset >= len) {
> + /* got last byte */
> + s->loc[locty].sts = STS_VALID;
