From: Omar Sandoval <osandov@xxxxxx>
We've encountered a particular model of STMicroelectronics TPM that
transiently returns a bad value in the status register. This causes the
kernel to believe that the TPM is ready to receive a command when it
actually isn't, which in turn causes the send to time out in
get_burstcount(). In testing, reading the status register one extra time
convinces the TPM to return a valid value.
Signed-off-by: Omar Sandoval <osandov@xxxxxx>
---
drivers/char/tpm/tpm_tis_core.c | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 27c6ca031e23..5a2f6acaf768 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -238,6 +238,25 @@ static u8 tpm_tis_status(struct tpm_chip *chip)
rc = tpm_tis_read8(priv, TPM_STS(priv->locality), &status);
if (rc < 0)
return 0;
+ /*
+ * Some STMicroelectronics TPMs have a bug where the status register is
+ * sometimes bogus (all 1s) if read immediately after the access
+ * register is written to. Bits 0, 1, and 5 are always supposed to read
+ * as 0, so this is clearly invalid. Reading the register a second time
+ * returns a valid value.
+ */
+ if (unlikely(status == 0xff)) {
+ rc = tpm_tis_read8(priv, TPM_STS(priv->locality), &status);
+ if (rc < 0)
+ return 0;
+ /*
+ * The status is somehow still bad. This hasn't been observed in
+ * practice, but clear it just in case so that it doesn't appear
+ * to be ready.
+ */
+ if (unlikely(status == 0xff))
+ status = 0;
+ }
return status;
}
--
2.26.1
