From: Nicolin Chen <redacted>
Sent: Wednesday, March 18, 2026 3:16 AM

An ATC invalidation timeout is a fatal error. While the SMMUv3 hardware is
aware of the timeout via a GERROR interrupt, the driver thread issuing the
commands lacks a direct mechanism to verify whether its specific batch was
the cause or not, as polling the CMD_SYNC status doesn't natively return a
failure code, making it very difficult to coordinate per-device recovery.

Introduce an atc_sync_timeouts bitmap in the cmdq structure to bridge this
gap. When the ISR detects an ATC timeout, set the bit corresponding to the
physical CMDQ index of the faulting CMD_SYNC command.

It's nice to see the ability of allowing sw to identify the faulting sync command
upon an ATC timeout! On VT-d it's not feasible when multiple wait descriptors
(similar to CMD_SYNC) are in-fly... :/