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

[Stephen Douthit]

On 03/19/2018 08:55 AM, Stefan Berger wrote:
> On 03/14/2018 03:42 PM, Kevin O'Connor wrote:
>> 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.

We don't need to force use of locality 0 for this polling.  LOC_STATE is
a single register aliased to all localities.  We can just start polling
on LOC_STATE immediately without the write.

There's also a note in the spec that locAssigned and activeLocality will
be set to 0 as their initial state after power on.

> If this one is controversal, the other two patches fix real bugs and we should consider applying them. I think for testing Stephen's feedback is primarily important on 1/3. Stephen, can you comment?

I think we can change this patch to something like this:

+#define CRB_STATE_VALID_STS 0b10000000
+#define CRB_STATE_LOC_ASSIGNED 0b00000010
+#define CRB_STATE_READY_MASK (CRB_STATE_VALID_STS | CRB_STATE_LOC_ASSIGNED)
+
  /* if device is not there, return '0', '1' otherwise */
  static u32 crb_probe(void)
  {
      if (!CONFIG_TCGBIOS)
          return 0;

+    /* Wait for the interface to report it's ready */
+    u32 rc = crb_wait_reg(0, CRB_REG_LOC_STATE, TIS2_DEFAULT_TIMEOUT_D,
+                          CRB_STATE_READY_MASK, CRB_STATE_VALID_STS);
+    if (rc)
+        return 0;
+

I tested this on my system (2.0 TPM using FIFO interface) in the present
and absent and it works as expected.  This testing misses the CRB device
present case though.

-Steve