Platforms that support FF-A direct message request v2 can implement Secure Partitions (SPs) that host multiple services. When the TPM service shares its SP with other services, message requests from the driver may fail with a BUSY response if another service is currently active.
To improve robustness in such scenarios, we need to introduce retry logic in the driver. When a BUSY error is received, the driver will re-attempt the TPM request until it succeeds or a configurable timeout (default: 2000 ms) is reached. This ensures reliable TPM access under shared-SP conditions. Add a module parameter, `busy_timeout`, which specifies the maximum amount of time (in milliseconds) to retry on BUSY before giving up. This change builds on top of commit a85b55ee64a5, which introduced support for TPM service communication using the FF-A direct message v2 path, in accordance with section 3.3 of the TPM Service Command Response Buffer Interface specification. https://developer.arm.com/documentation/den0138/latest/ Changes in v4: - Updated commit message to clarify the purpose of the patch. - Removed comments that state the obvious. Prachotan Bathi (1): tpm_crb_ffa: handle tpm busy return code drivers/char/tpm/tpm_crb_ffa.c | 74 +++++++++++++++++++++++----------- 1 file changed, 50 insertions(+), 24 deletions(-) -- 2.43.0
