drm/nouveau: bring back blit subchannel for pre nv50 GPUs

1ba6113a90a0 removed a lot of the kernel GPU channel, but method 0x128
was important as otherwise the GPU spams us with `CACHE_ERROR` messages.

We use the blit subchannel inside our vblank handling, so we should keep
at least this part.

v2: Only do it for NV11+ GPUs

Closes: https://gitlab.freedesktop.org/drm/nouveau/-/issues/201
Fixes: 4a16dd9 ("drm/nouveau/kms: switch to drm fbdev helpers")
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230526091052.2169044-1-kherbst@redhat.com

Author: karolherbst

drivers/gpu/drm/nouveau/nouveau_chan.c

@@ -90,6 +90,7 @@ nouveau_channel_del(struct nouveau_channel **pchan)
 		if (cli)
 			nouveau_svmm_part(chan->vmm->svmm, chan->inst);
 
+		nvif_object_dtor(&chan->blit);
 		nvif_object_dtor(&chan->nvsw);
 		nvif_object_dtor(&chan->gart);
 		nvif_object_dtor(&chan->vram);

drivers/gpu/drm/nouveau/nouveau_chan.h

@@ -53,6 +53,7 @@ struct nouveau_channel {
 	u32 user_put;
 
 	struct nvif_object user;
+	struct nvif_object blit;
 
 	struct nvif_event kill;
 	atomic_t killed;

drivers/gpu/drm/nouveau/nouveau_drm.c

@@ -375,15 +375,29 @@ nouveau_accel_gr_init(struct nouveau_drm *drm)
 		ret = nvif_object_ctor(&drm->channel->user, "drmNvsw",
 				       NVDRM_NVSW, nouveau_abi16_swclass(drm),
 				       NULL, 0, &drm->channel->nvsw);
+
+		if (ret == 0 && device->info.chipset >= 0x11) {
+			ret = nvif_object_ctor(&drm->channel->user, "drmBlit",
+					       0x005f, 0x009f,
+					       NULL, 0, &drm->channel->blit);
+		}
+
 		if (ret == 0) {
 			struct nvif_push *push = drm->channel->chan.push;
-			ret = PUSH_WAIT(push, 2);
-			if (ret == 0)
+			ret = PUSH_WAIT(push, 8);
+			if (ret == 0) {
+				if (device->info.chipset >= 0x11) {
+					PUSH_NVSQ(push, NV05F, 0x0000, drm->channel->blit.handle);
+					PUSH_NVSQ(push, NV09F, 0x0120, 0,
+							       0x0124, 1,
+							       0x0128, 2);
+				}
 				PUSH_NVSQ(push, NV_SW, 0x0000, drm->channel->nvsw.handle);
+			}
 		}
 
 		if (ret) {
-			NV_ERROR(drm, "failed to allocate sw class, %d\n", ret);
+			NV_ERROR(drm, "failed to allocate sw or blit class, %d\n", ret);
 			nouveau_accel_gr_fini(drm);
 			return;
 		}