[PATCH v4 1/2] tpm: reduce poll sleep time in tpm_transmit()

[Nayna Jain]

tpm_try_transmit currently checks TPM status every 5 msecs between
send and recv. It does so in a loop for the maximum timeout as defined
in the TPM Interface Specification. However, the TPM may return before
5 msecs. Thus the polling interval for each iteration can be reduced,
which improves overall performance. This patch changes the polling sleep
time from 5 msecs to 1 msec.

Additionally, this patch renames TPM_POLL_SLEEP to TPM_TIMEOUT_POLL and
moves it to tpm.h as an enum value.

After this change, performance on a system[1] with a TPM 1.2 with an 8 byte
burstcount for 1000 extends improved from ~14 sec to ~10.7 sec.

[1] All tests are performed on an x86 based, locked down, single purpose
closed system. It has Infineon TPM 1.2 using LPC Bus.

Signed-off-by: Nayna Jain <na...@linux.vnet.ibm.com>
Reviewed-by: Mimi Zohar <zo...@linux.vnet.ibm.com>
Acked-by: Jay Freyensee <why2jjj.li...@gmail.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com>
---
 drivers/char/tpm/tpm-interface.c |  2 +-
 drivers/char/tpm/tpm.h           |  3 ++-
 drivers/char/tpm/tpm_tis_core.c  | 10 ++--------
 3 files changed, 5 insertions(+), 10 deletions(-)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index 9e80a953d693..a676d8ad5992 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -470,7 +470,7 @@ ssize_t tpm_transmit(struct tpm_chip *chip, struct 
tpm_space *space,
                        goto out;
                }
 
-               tpm_msleep(TPM_TIMEOUT);
+               tpm_msleep(TPM_TIMEOUT_POLL);
                rmb();
        } while (time_before(jiffies, stop));
 
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index f895fba4e20d..7e797377e1eb 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -53,7 +53,8 @@ enum tpm_const {
 enum tpm_timeout {
        TPM_TIMEOUT = 5,        /* msecs */
        TPM_TIMEOUT_RETRY = 100, /* msecs */
-       TPM_TIMEOUT_RANGE_US = 300      /* usecs */
+       TPM_TIMEOUT_RANGE_US = 300,     /* usecs */
+       TPM_TIMEOUT_POLL = 1    /* msecs */
 };
 
 /* TPM addresses */
diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c
index da074e3db19b..021e6b68f2db 100644
--- a/drivers/char/tpm/tpm_tis_core.c
+++ b/drivers/char/tpm/tpm_tis_core.c
@@ -31,12 +31,6 @@
 #include "tpm.h"
 #include "tpm_tis_core.h"
 
-/* This is a polling delay to check for status and burstcount.
- * As per ddwg input, expectation is that status check and burstcount
- * check should return within few usecs.
- */
-#define TPM_POLL_SLEEP 1  /* msec */
-
 static void tpm_tis_clkrun_enable(struct tpm_chip *chip, bool value);
 
 static bool wait_for_tpm_stat_cond(struct tpm_chip *chip, u8 mask,
@@ -90,7 +84,7 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask,
                }
        } else {
                do {
-                       tpm_msleep(TPM_POLL_SLEEP);
+                       tpm_msleep(TPM_TIMEOUT_POLL);
                        status = chip->ops->status(chip);
                        if ((status & mask) == mask)
                                return 0;
@@ -232,7 +226,7 @@ static int get_burstcount(struct tpm_chip *chip)
                burstcnt = (value >> 8) & 0xFFFF;
                if (burstcnt)
                        return burstcnt;
-               tpm_msleep(TPM_POLL_SLEEP);
+               tpm_msleep(TPM_TIMEOUT_POLL);
        } while (time_before(jiffies, stop));
        return -EBUSY;
 }
-- 
2.13.3