RE: [PATCH v2 4/7] iommu/arm-smmu-v3: Mark ATC invalidate timeouts via lockless bitmap

[Tian, Kevin]

> From: Nicolin Chen <nicolinc@xxxxxxxxxx>
> 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... :/