[PATCH v2 0/2] tpm: improving granularity in poll sleep times

[PATCH v2 0/2] tpm: improving granularity in poll sleep times

[Nayna Jain]

The existing TPM polling code sleeps in each loop iteration for time in
msecs ranging from 1 msecs to 5 msecs. However, many of the TPM commands
complete much faster, resulting in unnecessary delays.

This set of patches identifies such iterations and optimizes the sleep
time. The first patch replaces TPM_POLL_SLEEP with TPM_TIMEOUT_POLL and
moves it from tpm_tis_core.c to tpm.h as an enum with value 1 msecs. The
second patch further reduces the TPM poll sleep time in get_burstcount()
and wait_for_tpm_stat() in tpm_tis_core.c by calling usleep_range()
directly.

The change is only in the polling time, and the maximum timeout is still
maintained the same. Thus, it should not affect the overall existing
behavior. 

Changelog:
 
v2:

tpm: reduce poll sleep time in tpm_transmit()
* merged previously defined two patches into this. 
* updated patch description as per Jarkko's feedback

tpm: reduce polling time to usecs for even finer granularity
* directly use usleep_range with finer granularity less than 1msec

Nayna Jain (2):
  tpm: reduce poll sleep time in tpm_transmit()
  tpm: reduce polling time to usecs for even finer granularity

 drivers/char/tpm/tpm-interface.c |  2 +-
 drivers/char/tpm/tpm.h           |  5 ++++-
 drivers/char/tpm/tpm_tis_core.c  | 11 +++--------
 3 files changed, 8 insertions(+), 10 deletions(-)

-- 
2.13.3

[PATCH v2 1/2] tpm: reduce poll sleep time in tpm_transmit()

[Nayna Jain]

The TPM polling code in tpm_transmit sleeps in each loop iteration for
5 msecs. However, the TPM might return earlier, and thus waiting for
5 msecs adds an unnecessary delay. This patch reduces the polling sleep
time in tpm_transmit() from 5 msecs to 1 msecs.

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

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

Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.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

[PATCH v2 2/2] tpm: reduce polling time to usecs for even finer granularity

[Nayna Jain]

The TPM burstcount and status commands are supposed to return very
quickly [1][2]. 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 TPM 1.2 with an 8 byte burstcount for
1000 extends improved from ~10.7 sec to ~7 sec.

[1] From 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."

[2] From 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 <nayna@linux.vnet.ibm.com>
---
 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 7e797377e1eb..f0e4d290c347 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 021e6b68f2db..5bba5c662423 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;
@@ -226,7 +227,7 @@ 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;
 }
-- 
2.13.3

Re: [PATCH v2 1/2] tpm: reduce poll sleep time in tpm_transmit()

[Mimi Zohar]

On Tue, 2018-04-17 at 09:12 -0400, Nayna Jain wrote:
> The TPM polling code in tpm_transmit sleeps in each loop iteration for
> 5 msecs. However, the TPM might return earlier, and thus waiting for
> 5 msecs adds an unnecessary delay. This patch reduces the polling sleep
> time in tpm_transmit() from 5 msecs to 1 msecs.
> 
> Additionally, this patch renames TPM_POLL_SLEEP and moves it to tpm.h as
> an enum value.
> 
> After this change, performance on a TPM 1.2 with an 8 byte burstcount
> for 1000 extends improved from ~14 sec to ~10.7 sec.
> 
> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>

Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.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;
>  }

Re: [PATCH v2 2/2] tpm: reduce polling time to usecs for even finer granularity

[Mimi Zohar]

On Tue, 2018-04-17 at 09:12 -0400, Nayna Jain wrote:
> The TPM burstcount and status commands are supposed to return very
> quickly [1][2]. 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 TPM 1.2 with an 8 byte burstcount for
> 1000 extends improved from ~10.7 sec to ~7 sec.
> 
> [1] From 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."
> 
> [2] From 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 <nayna@linux.vnet.ibm.com>

Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com>


> ---
>  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 7e797377e1eb..f0e4d290c347 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 021e6b68f2db..5bba5c662423 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;
> @@ -226,7 +227,7 @@ 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;
>  }

Re: [PATCH v2 1/2] tpm: reduce poll sleep time in tpm_transmit()

[Jarkko Sakkinen]

On Tue, Apr 17, 2018 at 09:12:45AM -0400, Nayna Jain wrote:
> The TPM polling code in tpm_transmit sleeps in each loop iteration for
> 5 msecs. However, the TPM might return earlier, and thus waiting for
> 5 msecs adds an unnecessary delay. This patch reduces the polling sleep
> time in tpm_transmit() from 5 msecs to 1 msecs.

I'm not sure what TPM returning earlier has to do with this. TPM probably
never returns exactly in the spec defined timeout/duration. I just don't
understand reasoning in this paragraph.

> Additionally, this patch renames TPM_POLL_SLEEP and moves it to tpm.h as
> an enum value.
> 
> After this change, performance on a TPM 1.2 with an 8 byte burstcount
> for 1000 extends improved from ~14 sec to ~10.7 sec.

You cannot give absolute numbers without a context (platform, software).

> Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>

/Jarkko

Re: [PATCH v2 2/2] tpm: reduce polling time to usecs for even finer granularity

[Jarkko Sakkinen]

On Tue, Apr 17, 2018 at 09:12:46AM -0400, Nayna Jain wrote:
> The TPM burstcount and status commands are supposed to return very
> quickly [1][2]. 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 TPM 1.2 with an 8 byte burstcount for
> 1000 extends improved from ~10.7 sec to ~7 sec.
> 
> [1] From 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."
> 
> [2] From 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 <nayna@linux.vnet.ibm.com>

Great, thanks for finding those references. Kind of stuff that I will
forget within months and have to revisit with git blame/log :-)

Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>

/Jarkko