[can] add TX quiesce full flush and abort

[wdfk-prog]

Summary

Add explicit TX lifecycle operations on top of PR #9.

This layer introduces:

• QUIESCING / QUIESCED TX lifecycle transitions;
• DRAIN, DROP_QUEUED, and ABORT_ALL policies;
• RT_CAN_CAP_TX_ABORT capability;
• per-mailbox abort through RT_CAN_CMD_ABORT_TX;
• full TX flush through RT_CAN_CMD_FLUSH_TX;
• explicit TX resume;
• runtime baud-rate changes through quiesce -> abort-all -> reconfigure -> resume.

Quiesce semantics

New TX admission is rejected as soon as lifecycle enters QUIESCING.

• DRAIN: already accepted queued requests continue through the normal scheduler until TX becomes idle.
• DROP_QUEUED: software-queued requests are cancelled; hardware-owned requests are allowed to terminate normally.
• ABORT_ALL: software-queued requests are cancelled and hardware-owned requests are moved to ABORTING, then the driver is asked to abort each mailbox.

A successful hardware abort request is not treated as terminal by itself. The request remains owned until the driver reports the mailbox terminal event, preserving exactly-once retirement in abort/TX_DONE races.

Full flush

RT_CAN_CMD_FLUSH_TX maps to RT_CAN_QUIESCE_ABORT_ALL. It returns only after the TX engine reaches QUIESCED, or returns timeout if hardware-owned work cannot be retired.

Runtime bitrate

RT_CAN_CMD_SET_BAUD is performed from a quiesced TX boundary and resumes admission after a successful driver reconfiguration.

Compatibility

• No deferred/workqueue TX execution is introduced.
• Existing BSP rt_hw_can_isr() calls remain unchanged.
• Drivers without abort capability may still use DRAIN/DROP_QUEUED; ABORT_ALL cannot retire hardware-owned requests without a terminal event and therefore times out rather than reusing ownership unsafely.

Tests

The fake-controller test covers an ABORT_ALL quiesce with one hardware-owned request and one software-queued request, synchronous abort completion, transition to QUIESCED, and explicit resume.

No target-board/hardware validation has been performed in this PR.

Stack

PR 5/7. Base: PR #9 (refactor/can-strict-tx-order).

[github-actions]

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