drm/nouveau/fifo/tu102: Turing channel preemption fix

Previous hardware allowed a MMU fault to be generated by software to
trigger a context switch for engine recovery. Turing has the capability
to preempt all work from a specific runlist processor and removed the
registers currently used for triggering MMU faults. Attempting to access
these non-existent registers results in further errors, so use the
runlist preemption register instead.
Signed-off-by: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nvkm/engine/fifo/tu102.c

@@ -144,7 +144,6 @@ tu102_fifo_recover_work(struct work_struct *w)
 	for (todo = runm; runl = __ffs(todo), todo; todo &= ~BIT(runl))
 		gk104_fifo_runlist_update(fifo, runl);
 
-	nvkm_wr32(device, 0x00262c, runm);
 	nvkm_mask(device, 0x002630, runm, 0x00000000);
 }
 
@@ -240,13 +239,11 @@ tu102_fifo_recover_chan(struct nvkm_fifo *base, int chid)
 static void
 tu102_fifo_recover_engn(struct gk104_fifo *fifo, int engn)
 {
-	struct nvkm_engine *engine = fifo->engine[engn].engine;
 	struct nvkm_subdev *subdev = &fifo->base.engine.subdev;
 	struct nvkm_device *device = subdev->device;
 	const u32 runl = fifo->engine[engn].runl;
 	const u32 engm = BIT(engn);
 	struct gk104_fifo_engine_status status;
-	int mmui = -1;
 
 	assert_spin_locked(&fifo->base.lock);
 	if (fifo->recover.engm & engm)
@@ -263,44 +260,8 @@ tu102_fifo_recover_engn(struct gk104_fifo *fifo, int engn)
 		tu102_fifo_recover_chan(&fifo->base, status.chan->id);
 	}
 
-	/* Determine MMU fault ID for the engine, if we're not being
-	 * called from the fault handler already.
-	 */
-	if (!status.faulted && engine) {
-		mmui = nvkm_top_fault_id(device, engine->subdev.index);
-		if (mmui < 0) {
-			const struct nvkm_enum *en = fifo->func->fault.engine;
-
-			for (; en && en->name; en++) {
-				if (en->data2 == engine->subdev.index) {
-					mmui = en->value;
-					break;
-				}
-			}
-		}
-		WARN_ON(mmui < 0);
-	}
-
-	/* Trigger a MMU fault for the engine.
-	 *
-	 * No good idea why this is needed, but nvgpu does something similar,
-	 * and it makes recovery from CTXSW_TIMEOUT a lot more reliable.
-	 */
-	if (mmui >= 0) {
-		nvkm_wr32(device, 0x002a30 + (engn * 0x04), 0x00000100 | mmui);
-
-		/* Wait for fault to trigger. */
-		nvkm_msec(device, 2000,
-			gk104_fifo_engine_status(fifo, engn, &status);
-			if (status.faulted)
-				break;
-		);
-
-		/* Release MMU fault trigger, and ACK the fault. */
-		nvkm_wr32(device, 0x002a30 + (engn * 0x04), 0x00000000);
-		nvkm_wr32(device, 0x00259c, BIT(mmui));
-		nvkm_wr32(device, 0x002100, 0x10000000);
-	}
+	/* Preempt the runlist */
+	nvkm_wr32(device, 0x2638, BIT(runl));
 
 	/* Schedule recovery. */
 	nvkm_warn(subdev, "engine %d: scheduled for recovery\n", engn);