[SeaBIOS] [PATCH 1/3] tpm: Wait for tpmRegValidSts flags on CRQ interface before probing

[Kevin O'Connor]

On Wed, Mar 14, 2018 at 01:42:41PM -0400, Stefan Berger wrote:
> Wait for the tpmRegValidSts flag on the TPM_LOC_STATE_x register.
> 
> Since it's not quite clear when this flag may become valid, we request
> access to the interace on locality 0, which must then make it valid.
> 
> Signed-off-by: Stefan Berger <stefanb at linux.vnet.ibm.com>
> ---
>  src/hw/tpm_drivers.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/src/hw/tpm_drivers.c b/src/hw/tpm_drivers.c
> index ed58bf5..ad97f67 100644
> --- a/src/hw/tpm_drivers.c
> +++ b/src/hw/tpm_drivers.c
> @@ -374,12 +374,23 @@ static u32 tis_waitrespready(enum tpmDurationType to_t)
>      return rc;
>  }
>  
> +#define CRB_STATE_VALID_STS 0b10000000
> +
>  /* if device is not there, return '0', '1' otherwise */
>  static u32 crb_probe(void)
>  {
>      if (!CONFIG_TCGBIOS)
>          return 0;
>  
> +    /* request access -- this must cause a valid STS flag */
> +    writeb(CRB_REG(0, CRB_REG_LOC_CTRL), 1);

Would it be possible to do a sanity check with read operations before
doing a write operation?  The fear is that the device is not present
and the write operation corrupts some other device, causes a bus
error, or something else undesirable.

-Kevin