[SeaBIOS] [PATCH v2 1/3] tpm: Wait for tpmRegValidSts flag on CRQ interface before probing

Kevin O'Connor kevin at koconnor.net
Sun Mar 25 17:45:07 CEST 2018

On Thu, Mar 22, 2018 at 08:19:09AM -0400, Stefan Berger wrote:
> The timeout to wait for the register change is 30ms. We yield() while
> waiting, so we don't block everything entirely... Is the error message
> misleading and we should print out that a device was not detected or print
> out if it is detected instead?

Unfortunately, although the TPM code calls yield(), there isn't
anything else running at that point, so the delay still directly
impacts the total boot time.  It's not easy to push back the TPM
initialization so that other "threads" are running in parallel,
because the TPM code wants to be initialized prior to running option
roms and other devices.

Could we do something like the below (completely untested)?  I don't
think we have to wait for the TPM device to report ready, because in a
real world scenario it would take an x86 cpu hundreds of milliseconds
from power on to get to this point of the code anyway.


--- a/src/hw/tpm_drivers.c
+++ b/src/hw/tpm_drivers.c
@@ -78,7 +78,8 @@ static u32 wait_reg8(u8* reg, u32 time, u8 mask, u8 expect)
         if (timer_check(end)) {
-            warn_timeout();
+            if (time)
+                warn_timeout();
@@ -108,7 +109,7 @@ static u32 tis_probe(void)
         return 0;
     /* Wait for the interface to report it's ready */
-    u32 rc = tis_wait_access(0, TIS_DEFAULT_TIMEOUT_A,
+    u32 rc = tis_wait_access(0, 0,
     if (rc)
@@ -385,7 +386,7 @@ static u32 crb_probe(void)
         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,
+    u32 rc = crb_wait_reg(0, CRB_REG_LOC_STATE, 0,
                           CRB_STATE_READY_MASK, CRB_STATE_VALID_STS);
     if (rc)
         return 0;

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