1. 10 2月, 2016 1 次提交
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      TPM: Retry SaveState command in suspend path · 32d33b29
      Duncan Laurie 提交于
      If the TPM has already been sent a SaveState command before the driver
      is loaded it may have problems sending that same command again later.
      
      This issue is seen with the Chromebook Pixel due to a firmware bug in
      the legacy mode boot path which is sending the SaveState command
      before booting the kernel.  More information is available at
      http://crbug.com/203524
      
      This change introduces a retry of the SaveState command in the suspend
      path in order to work around this issue.  A future firmware update
      should fix this but this is also a trivial workaround in the driver
      that has no effect on systems that do not show this problem.
      
      When this does happen the TPM responds with a non-fatal TPM_RETRY code
      that is defined in the specification:
      
        The TPM is too busy to respond to the command immediately, but the
        command could be resubmitted at a later time.  The TPM MAY return
        TPM_RETRY for any command at any time.
      
      It can take several seconds before the TPM will respond again.  I
      measured a typical time between 3 and 4 seconds and the timeout is set
      at a safe 5 seconds.
      
      It is also possible to reproduce this with commands via /dev/tpm0.
      The bug linked above has a python script attached which can be used to
      test for this problem.  I tested a variety of TPMs from Infineon,
      Nuvoton, Atmel, and STMicro but was only able to reproduce this with
      LPC and I2C TPMs from Infineon.
      
      The TPM specification only loosely defines this behavior:
      
        TPM Main Level 2 Part 3 v1.2 r116, section 3.3. TPM_SaveState:
        The TPM MAY declare all preserved values invalid in response to any
        command other than TPM_Init.
      
        TCG PC Client BIOS Spec 1.21 section 8.3.1.
        After issuing a TPM_SaveState command, the OS SHOULD NOT issue TPM
        commands before transitioning to S3 without issuing another
        TPM_SaveState command.
      
        TCG PC Client TIS 1.21, section 4. Power Management:
        The TPM_SaveState command allows a Static OS to indicate to the TPM
        that the platform may enter a low power state where the TPM will be
        required to enter into the D3 power state.  The use of the term "may"
        is significant in that there is no requirement for the platform to
        actually enter the low power state after sending the TPM_SaveState
        command.  The software may, in fact, send subsequent commands after
        sending the TPM_SaveState command.
      
      Change-Id: I52b41e826412688e5b6c8ddd3bb16409939704e9
      Signed-off-by: NDuncan Laurie <dlaurie@chromium.org>
      Signed-off-by: NKent Yoder <key@linux.vnet.ibm.com>
      32d33b29
  12. 05 2月, 2013 6 次提交
  13. 10 10月, 2012 1 次提交
  14. 23 8月, 2012 4 次提交
  15. 11 7月, 2012 1 次提交
  16. 15 2月, 2012 1 次提交