[PATCH v4 0/1] tpm_crb_ffa: handle tpm busy return code

[Prachotan Bathi <prachotan.bathi@arm.com>]

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(-)

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2.43.0