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+What: /sys/class/tpm/tpmX/ppi/
+Date: August 2012
+KernelVersion: 3.6
+Contact: xiaoyan.zhang@intel.com
+Description:
+ This folder includes the attributes related with PPI (Physical
+ Presence Interface). Only if TPM is supported by BIOS, this
+ folder makes sense. The folder path can be got by command
+ 'find /sys/ -name 'pcrs''. For the detail information of PPI,
+ please refer to the PPI specification from
+
+ http://www.trustedcomputinggroup.org/
+
+ In Linux 4.2 ppi was moved to the character device directory.
+ A symlink from tpmX/device/ppi to tpmX/ppi to provide backwards
+ compatibility.
+
+What: /sys/class/tpm/tpmX/ppi/version
+Date: August 2012
+Contact: xiaoyan.zhang@intel.com
+Description:
+ This attribute shows the version of the PPI supported by the
+ platform.
+ This file is readonly.
+
+What: /sys/class/tpm/tpmX/ppi/request
+Date: August 2012
+Contact: xiaoyan.zhang@intel.com
+Description:
+ This attribute shows the request for an operation to be
+ executed in the pre-OS environment. It is the only input from
+ the OS to the pre-OS environment. The request should be an
+ integer value range from 1 to 160, and 0 means no request.
+ This file can be read and written.
+
+What: /sys/class/tpm/tpmX/ppi/response
+Date: August 2012
+Contact: xiaoyan.zhang@intel.com
+Description:
+ This attribute shows the response to the most recent operation
+ request it acted upon. The format is "<request> <response num>
+ : <response description>".
+ This file is readonly.
+
+What: /sys/class/tpm/tpmX/ppi/transition_action
+Date: August 2012
+Contact: xiaoyan.zhang@intel.com
+Description:
+ This attribute shows the platform-specific action that should
+ take place in order to transition to the BIOS for execution of
+ a requested operation. The format is "<action num>: <action
+ description>".
+ This file is readonly.
+
+What: /sys/class/tpm/tpmX/ppi/tcg_operations
+Date: August 2012
+Contact: xiaoyan.zhang@intel.com
+Description:
+ This attribute shows whether it is allowed to request an
+ operation to be executed in the pre-OS environment by the BIOS
+ for the requests defined by TCG, i.e. requests from 1 to 22.
+ The format is "<request> <status num>: <status description>".
+ This attribute is only supported by PPI version 1.2+.
+ This file is readonly.
+
+What: /sys/class/tpm/tpmX/ppi/vs_operations
+Date: August 2012
+Contact: xiaoyan.zhang@intel.com
+Description:
+ This attribute shows whether it is allowed to request an
+ operation to be executed in the pre-OS environment by the BIOS
+ for the verdor specific requests, i.e. requests from 128 to
+ 255. The format is same with tcg_operations. This attribute
+ is also only supported by PPI version 1.2+.
+ This file is readonly.