Add CFG_CONCURRENT_SINGLE_INSTANCE_TA

[jforissier]

Commit 2b07dcb ("core: avoid deadlocks caused by single-instance
TA") introduces a lock that allows only one single instance TA to be
executing at any time. While it does address the risk of deadlock that
can arise when several single instance TAs call each other, it also
puts a serious performance limitation on multi-core platforms, which
could otherwise execute several unrelated single instance TAs
simultaneously.

This commit makes the single instance lock optional. By setting
CFG_CONCURRENT_SINGLE_INSTANCE_TA=y, the lock is disabled and TAs are
allowed to run concurrently. In the future, we may implement a deadlock
detection algorithm; in the meantime, this simple solution should be
enough to cover the current use cases.

Signed-off-by: Jerome Forissier jerome.forissier@linaro.org
Tested-by: Jerome Forissier jerome.forissier@linaro.org (HiKey960)
CC: Zeng Tao prime.zeng@hisilicon.com

[jenswi-linaro]

Acked-by: Jens Wiklander <jens.wiklander@linaro.org>

[etienne-lms]

Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>
Change is OK but I wonder if this feature could be TA related, through a TA_FLAG_SINGLE_INSTANCE_CONCURRENCY so that TA can explicitly claim this non-protection.

[jforissier]

@etienne-lms a TA flag would certainly be doable but would be more complex (what should be the rules when mixing TAs that have the flag with TAs that don't have it?). I'm not sure it's worth the trouble.