tpm: reduce poll sleep time in tpm_transmit()

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 <[email protected]>
Acked-by: Jay Freyensee <[email protected]>
Reviewed-by: Jarkko Sakkinen <[email protected]>
Tested-by: Jarkko Sakkinen <[email protected]>
Signed-off-by: Jarkko Sakkinen <[email protected]>

Author: naynajain

drivers/char/tpm/tpm-interface.c

@@ -489,7 +489,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip *chip,
 			goto out;
 		}
 
-		tpm_msleep(TPM_TIMEOUT);
+		tpm_msleep(TPM_TIMEOUT_POLL);
 		rmb();
 	} while (time_before(jiffies, stop));
 

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 */

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;
@@ -279,7 +273,7 @@ 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;
 }