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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 <nayna@linux.vnet.ibm.com> Reviewed-by: Mimi Zohar <zohar@linux.vnet.ibm.com> Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> Acked-by: Jay Freyensee <why2jjj.linux@gmail.com> Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.