drm/nouveau/pmu/gm200-: avoid touching PMU outside of DEVINIT/PREOS/ACR

There have been reports of the WFI timing out on some boards, and a
patch was proposed to just remove it.  This stuff is rather fragile,
and I believe the WFI might be needed with our FW prior to GM200.

However, we probably should not be touching PMU during init on GPUs
where we depend on NVIDIA FW, outside of limited circumstances, so
this should be a somewhat safer change that achieves the desired
result.
Reported-by: Diego Viola <diego.viola@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://gitlab.freedesktop.org/drm/nouveau/-/merge_requests/10

drivers/gpu/drm/nouveau/nvkm/subdev/pmu/base.c

@@ -94,20 +94,13 @@ nvkm_pmu_fini(struct nvkm_subdev *subdev, bool suspend)
 	return 0;
 }
 
-static int
+static void
 nvkm_pmu_reset(struct nvkm_pmu *pmu)
 {
 	struct nvkm_device *device = pmu->subdev.device;
 
 	if (!pmu->func->enabled(pmu))
-		return 0;
-
-	/* Inhibit interrupts, and wait for idle. */
-	nvkm_wr32(device, 0x10a014, 0x0000ffff);
-	nvkm_msec(device, 2000,
-		if (!nvkm_rd32(device, 0x10a04c))
-			break;
-	);
+		return;
 
 	/* Reset. */
 	if (pmu->func->reset)
@@ -118,25 +111,37 @@ nvkm_pmu_reset(struct nvkm_pmu *pmu)
 		if (!(nvkm_rd32(device, 0x10a10c) & 0x00000006))
 			break;
 	);
-
-	return 0;
 }
 
 static int
 nvkm_pmu_preinit(struct nvkm_subdev *subdev)
 {
 	struct nvkm_pmu *pmu = nvkm_pmu(subdev);
-	return nvkm_pmu_reset(pmu);
+	nvkm_pmu_reset(pmu);
+	return 0;
 }
 
 static int
 nvkm_pmu_init(struct nvkm_subdev *subdev)
 {
 	struct nvkm_pmu *pmu = nvkm_pmu(subdev);
-	int ret = nvkm_pmu_reset(pmu);
-	if (ret == 0 && pmu->func->init)
-		ret = pmu->func->init(pmu);
-	return ret;
+	struct nvkm_device *device = pmu->subdev.device;
+
+	if (!pmu->func->init)
+		return 0;
+
+	if (pmu->func->enabled(pmu)) {
+		/* Inhibit interrupts, and wait for idle. */
+		nvkm_wr32(device, 0x10a014, 0x0000ffff);
+		nvkm_msec(device, 2000,
+			if (!nvkm_rd32(device, 0x10a04c))
+				break;
+		);
+
+		nvkm_pmu_reset(pmu);
+	}
+
+	return pmu->func->init(pmu);
 }
 
 static void *