CXL mailbox background command

["Dai WeiBin \(David Dai\)" <david.dai@montage-tech.com>]

Hi Ben,

When we think of cxl mailbox background command, we met a difficult issue, how to handle switching between a background command end and another background command start?

The flow is as below:
1. Host/caller sends a command to cxl device.
2. CXL device identifies the command as a background command, then cxl device returns background command started, background Operation is set to 1.
3. CXL device start to handle background command.
4. Host/caller can send other commands to cxl device when background command is ongoing on device side.
5. At a special point host/caller is sending a command to device when the background command just is finished, the new command will be handled as a background command by device.
6. That means the old background command ends, background Operation is set to 0, immediately the new background command is started, background Operation is set to 1 again at once.
7. So Host driver doesn’t have a chance to check the old background command has been finished, it still see “background Operation == 1”.
8. Mailbox Status Register and Background Command Status Register are both read-only, that results there is not a handshake between host and device.
9.How to guarantee exclusion between two background commands.

Do you have any suggestion about this?

Thanks,
David