[Regression] TPM char device not created if TPM 1.2 is disabled, but visible

[Sahil Rihan]

(Please CC me on replies - I'm not subscribed to LMKL)

Prior to  0cf577a03f21 if a TPM 1.2 device was disabled, but visible (sysfs node "enabled" returns 0), creation of the TPM char device was only skipped if  tpm_bios_log_setup returned -ENODEV. 

On some systems like HP DL380 G9, if the TPM is disabled but visible, the TCPA log is empty, which means tpm_read_log_acpi returns -EIO.  Starting with 0cf577a03f21, -EIO triggers an early return from tpm_chip_register which means the char device is not created.

Log snippet:
[    4.320387] tpm_tis 00:00: 1.2 TPM (device-id 0xB, rev-id 16)
[    4.455389] tpm tpm0: A TPM error (7) occurred attempting to read a pcr value
[    4.457762] tpm tpm0: TPM is disabled/deactivated (0x7)
[    4.459461] tpm tpm0: tpm_read_log_acpi: TCPA log area empty    <----------------------
[    4.461312] tpm_tis: probe of 00:00 failed with error -5

Thanks,
Sahil