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spi/tpm.c do not waste time on wake pulses unless necessary 

The Cr50 secure chip implementation is guaranteed not to fall asleep
for 1 second after any SPI slave activity.

Let's not waste time on the wake up ping when it is not necessary.

BRANCH=cr50
BUG=b:68012381
TEST=using a protocol analyzer verified that the wake pulses are
     generated only when the new coreboot stage or depthcharge start,
     not on every SPI slave transaction.

Change-Id: Id8def1470ba3eab533075b9e7180f8a58e0b00b6
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://review.coreboot.org/22321
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
This commit is contained in:
Vadim Bendebury 2017-10-30 18:29:03 -07:00
parent eb72207fee
commit 3b62d6b40a
1 changed files with 31 additions and 7 deletions
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38
src/drivers/spi/tpm/tpm.c
View File

@ -110,19 +110,43 @@ static int start_transaction(int read_write, size_t bytes, unsigned addr)
int i;
struct stopwatch sw;
static int tpm_sync_needed CAR_GLOBAL;
static struct stopwatch wake_up_sw CAR_GLOBAL;
struct spi_slave *spi_slave = car_get_var_ptr(&g_spi_slave);
/*
* First Cr50 access in each coreboot stage where TPM is used will be
* prepended by a wake up pulse on the CS line.
*/
int wakeup_needed = 1;
/* Wait for tpm to finish previous transaction if needed */
if (car_get_var(tpm_sync_needed))
if (car_get_var(tpm_sync_needed)) {
tpm_sync();
else
/*
* During the first invocation of this function on each stage
* this if () clause code does not run (as tpm_sync_needed
* value is zero), during all following invocations the
* stopwatch below is guaranteed to be started.
*/
if (!stopwatch_expired(car_get_var_ptr(&wake_up_sw)))
wakeup_needed = 0;
} else {
car_set_var(tpm_sync_needed, 1);
}
/* Try to wake cr50 if it is asleep. */
spi_claim_bus(spi_slave);
udelay(1);
spi_release_bus(spi_slave);
udelay(100);
if (wakeup_needed) {
/* Just in case Cr50 is asleep. */
spi_claim_bus(spi_slave);
udelay(1);
spi_release_bus(spi_slave);
udelay(100);
}
/*
* The Cr50 on H1 does not go to sleep for 1 second after any
* SPI slave activity, let's be conservative and limit the
* window to 900 ms.
*/
stopwatch_init_msecs_expire(car_get_var_ptr(&wake_up_sw), 900);
/*
* The first byte of the frame header encodes the transaction type