From 424eaf910c329ab06ad03a527ef45dcf6a328f00 Mon Sep 17 00:00:00 2001 From: Nayna Jain Date: Wed, 16 May 2018 01:51:25 -0400 Subject: [PATCH] tpm: reduce polling time to usecs for even finer granularity MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The TPM burstcount and status commands are supposed to return very quickly [2][3]. This patch further reduces the TPM poll sleep time to usecs in get_burstcount() and wait_for_tpm_stat() by calling usleep_range() directly. After this change, performance on a system[1] with a TPM 1.2 with an 8 byte burstcount for 1000 extends improved from ~10.7 sec to ~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. [2] From the TCG Specification "TCG PC Client Specific TPM Interface Specification (TIS), Family 1.2": "NOTE : It takes roughly 330 ns per byte transfer on LPC. 256 bytes would take 84 us, which is a long time to stall the CPU. Chipsets may not be designed to post this much data to LPC; therefore, the CPU itself is stalled for much of this time. Sending 1 kB would take 350 μs. Therefore, even if the TPM_STS_x.burstCount field is a high value, software SHOULD be interruptible during this period." [3] From the TCG Specification 2.0, "TCG PC Client Platform TPM Profile (PTP) Specification": "It takes roughly 330 ns per byte transfer on LPC. 256 bytes would take 84 us. Chipsets may not be designed to post this much data to LPC; therefore, the CPU itself is stalled for much of this time. Sending 1 kB would take 350 us. Therefore, even if the TPM_STS_x.burstCount field is a high value, software should be interruptible during this period. For SPI, assuming 20MHz clock and 64-byte transfers, it would take about 120 usec to move 256B of data. Sending 1kB would take about 500 usec. If the transactions are done using 4 bytes at a time, then it would take about 1 msec. to transfer 1kB of data." Signed-off-by: Nayna Jain Reviewed-by: Mimi Zohar Reviewed-by: Jarkko Sakkinen Acked-by: Jay Freyensee Tested-by: Jarkko Sakkinen Signed-off-by: Jarkko Sakkinen --- drivers/char/tpm/tpm.h | 4 +++- drivers/char/tpm/tpm_tis_core.c | 5 +++-- 2 files changed, 6 insertions(+), 3 deletions(-) diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h index baa066997372..4426649e431c 100644 --- a/drivers/char/tpm/tpm.h +++ b/drivers/char/tpm/tpm.h @@ -54,7 +54,9 @@ enum tpm_timeout { TPM_TIMEOUT = 5, /* msecs */ TPM_TIMEOUT_RETRY = 100, /* msecs */ TPM_TIMEOUT_RANGE_US = 300, /* usecs */ - TPM_TIMEOUT_POLL = 1 /* msecs */ + TPM_TIMEOUT_POLL = 1, /* msecs */ + TPM_TIMEOUT_USECS_MIN = 100, /* usecs */ + TPM_TIMEOUT_USECS_MAX = 500 /* usecs */ }; /* TPM addresses */ diff --git a/drivers/char/tpm/tpm_tis_core.c b/drivers/char/tpm/tpm_tis_core.c index 7bfdec66be44..8b46aaa9e049 100644 --- a/drivers/char/tpm/tpm_tis_core.c +++ b/drivers/char/tpm/tpm_tis_core.c @@ -84,7 +84,8 @@ static int wait_for_tpm_stat(struct tpm_chip *chip, u8 mask, } } else { do { - tpm_msleep(TPM_TIMEOUT_POLL); + usleep_range(TPM_TIMEOUT_USECS_MIN, + TPM_TIMEOUT_USECS_MAX); status = chip->ops->status(chip); if ((status & mask) == mask) return 0; @@ -273,7 +274,7 @@ static int get_burstcount(struct tpm_chip *chip) burstcnt = (value >> 8) & 0xFFFF; if (burstcnt) return burstcnt; - tpm_msleep(TPM_TIMEOUT_POLL); + usleep_range(TPM_TIMEOUT_USECS_MIN, TPM_TIMEOUT_USECS_MAX); } while (time_before(jiffies, stop)); return -EBUSY; }