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@xxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> /Jarkko
