[PATCH] Fix Atmel TPM crash caused by too frequent queries

[Hao Wu <hao.wu@rubrik.com>]

Since kernel 4.14, we fixed the TPM sleep logic
from msleep to usleep_range, so that the TPM
sleeps exactly with TPM_TIMEOUT (=5ms) afterward.
Before that fix, msleep(5) actually sleeps for
around 15ms.
The fix is https://github.com/torvalds/linux/commit/9f3fc7bcddcb51234e23494531f93ab60475e1c3

That fix uncovered that the TPM_TIMEOUT was not properly
set previously. We recently found the TPM driver in kernel 4.14+
(including 5.9-rc4) crashes Atmel TPM chips with
too frequent TPM queries.

The TPM crash signature is
```
$ tpm_sealdata -z
Tspi_Key_LoadKey failed: 0x00001087 - layer=tddl, code=0087 (135), I/O error

$ sudo dmesg | grep tpm0
[59154.665549] tpm tpm0: tpm_try_transmit: send(): error -62
[59154.809532] tpm tpm0: tpm_try_transmit: send(): error -62
```

From the error code "-62", it looks similar to another bug
https://patchwork.kernel.org/patch/10520247/
where the "TPM_TIMEOUT_USECS_MAX" and "TPM_TIMEOUT_USEC_MIN"
is too small, which causes TPM get queried too frequently,
and thus crashes.

We finally found the root cause is related to
the sleep timeout used in `wait_for_tpm_stat`

In the 4.16, commit
https://github.com/torvalds/linux/commit/cf151a9a44d52a63332e8e926234574fe5a5d784
uses `TPM_POLL_SLEEP` instead of TPM_TIMEOUT for `wait_for_tpm_stat`
and set `TPM_POLL_SLEEP` (1ms).

Since 4.18 commits
https://github.com/torvalds/linux/commit/59f5a6b07f6434efac0057dc2f303a96b871811b
https://github.com/torvalds/linux/commit/424eaf910c329ab06ad03a527ef45dcf6a328f00
further reduced the timeout in wait_for_tpm_stat to less than 1ms.

Our patch here defines a `TPM_TIMEOUT_WAIT_STAT` (15ms) just for
`wait_for_tpm_stat the` to fix the crash in Atmel chips,
but not introduce unnecessary performance regression
in other workflows.
15ms is the actual timeout TPM chips use before the 4.14 fix
from msleep to usleep_range. Thus fixed the crash.

Exploring smaller `TPM_TIMEOUT_WAIT_STAT` should be a separate
thing to revisit later. This patch meant to fix the regression
introduced since 4.14

Test Plan:
- Run fixed kernel on system with Atmel TPM chips
  and ensure crash does not happen
- Run fixed kernel on system with other TPM chips
  (IFX / WEC / STM) ensure not breakages from tpm-tool

Signed-off-by: Hao Wu <hao.wu@rubrik.com>
---
 drivers/char/tpm/tpm.h          | 1 +
 drivers/char/tpm/tpm_tis_core.c | 3 +--
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index 947d1db0a5cc..899097ae9756 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -41,6 +41,7 @@ enum tpm_timeout {
 	TPM_TIMEOUT_RETRY = 100, /* msecs */
 	TPM_TIMEOUT_RANGE_US = 300,	/* usecs */
 	TPM_TIMEOUT_POLL = 1,	/* msecs */
+	TPM_TIMEOUT_WAIT_STAT = 15,      /* msecs */
 	TPM_TIMEOUT_USECS_MIN = 100,      /* usecs */
 	TPM_TIMEOUT_USECS_MAX = 500      /* usecs */
 };
diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index 65ab1b027949..8aa5eef10c28 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -80,8 +80,7 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
 		}
 	} else {
 		do {
-			usleep_range(TPM_TIMEOUT_USECS_MIN,
-				     TPM_TIMEOUT_USECS_MAX);
+			tpm_msleep(TPM_TIMEOUT_WAIT_STAT);
 			status = chip->ops->status(chip);
 			if ((status & mask) == mask)
 				return 0;
-- 
2.17.1