[RFC PATCH v3 4/9] accel: rocket: Reset the NPU before detaching the IOMMU on timeout

[Midgy BALON]

On a job timeout the NPU AXI master can be left wedged with
outstanding transactions. rocket_reset() detached the IOMMU group
before resetting the hardware, so iommu_detach_group() ->
__iommu_group_set_core_domain() asked the rk_iommu to stall and wait
for the in-flight transactions to drain. They never did, the stall
request timed out (-ETIMEDOUT) and the IOMMU core WARNed:

  WARNING: drivers/iommu/iommu.c:157 __iommu_group_set_core_domain
    iommu_detach_group
    rocket_reset
    rocket_job_timedout

Assert the core reset first: it quiesces the AXI master so the
following IOMMU detach completes cleanly. Move the detach after
rocket_core_reset() and out of the job_lock (it does not touch
in_flight_job).

Signed-off-by: Midgy BALON <midgy971 at gmail.com>
---
 drivers/accel/rocket/rocket_job.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/accel/rocket/rocket_job.c b/drivers/accel/rocket/rocket_job.c
index ac51bff39833f..e25234261536b 100644
--- a/drivers/accel/rocket/rocket_job.c
+++ b/drivers/accel/rocket/rocket_job.c
@@ -364,14 +364,20 @@ rocket_reset(struct rocket_core *core, struct drm_sched_job *bad)
 		if (core->in_flight_job)
 			pm_runtime_put_noidle(core->dev);
 
-		iommu_detach_group(NULL, core->iommu_group);
-
 		core->in_flight_job = NULL;
 	}
 
-	/* Proceed with reset now. */
+	/*
+	 * Reset the NPU hardware before detaching the IOMMU. A timed-out job
+	 * leaves the NPU AXI master wedged; detaching the IOMMU then issues a
+	 * stall request that never drains and times out (warning in the IOMMU
+	 * core). Asserting the core reset first quiesces the master so the
+	 * detach completes cleanly.
+	 */
 	rocket_core_reset(core);
 
+	iommu_detach_group(NULL, core->iommu_group);
+
 	/* NPU has been reset, we can clear the reset pending bit. */
 	atomic_set(&core->reset.pending, 0);
 
-- 
2.39.5