drm/nouveau: use system_wq instead of dev_priv->wq

With cmwq, there's no reason for nouveau to use a dedicated workqueue.
Drop dev_priv->wq and use system_wq instead.  Each work item is sync
flushed when the containing structure is unregistered/destroyed.

Note that this change also makes sure that nv50_gpio_handler is not
freed while the contained work item is still running.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: David Airlie <airlied@linux.ie>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/nouveau_drv.h

@@ -652,7 +652,6 @@ struct drm_nouveau_private {
 	/* interrupt handling */
 	void (*irq_handler[32])(struct drm_device *);
 	bool msi_enabled;
-	struct workqueue_struct *wq;
 	struct work_struct irq_work;
 
 	struct list_head vbl_waiting;

drivers/gpu/drm/nouveau/nouveau_state.c

@@ -929,12 +929,6 @@ int nouveau_load(struct drm_device *dev, unsigned long flags)
 	NV_DEBUG(dev, "vendor: 0x%X device: 0x%X class: 0x%X\n",
 		 dev->pci_vendor, dev->pci_device, dev->pdev->class);
 
-	dev_priv->wq = create_workqueue("nouveau");
-	if (!dev_priv->wq) {
-		ret = -EINVAL;
-		goto err_priv;
-	}
-
 	/* resource 0 is mmio regs */
 	/* resource 1 is linear FB */
 	/* resource 2 is RAMIN (mmio regs + 0x1000000) */
@@ -947,7 +941,7 @@ int nouveau_load(struct drm_device *dev, unsigned long flags)
 		NV_ERROR(dev, "Unable to initialize the mmio mapping. "
 			 "Please report your setup to " DRIVER_EMAIL "\n");
 		ret = -EINVAL;
-		goto err_wq;
+		goto err_priv;
 	}
 	NV_DEBUG(dev, "regs mapped ok at 0x%llx\n",
 					(unsigned long long)mmio_start_offs);
@@ -1054,8 +1048,6 @@ int nouveau_load(struct drm_device *dev, unsigned long flags)
 	iounmap(dev_priv->ramin);
 err_mmio:
 	iounmap(dev_priv->mmio);
-err_wq:
-	destroy_workqueue(dev_priv->wq);
 err_priv:
 	kfree(dev_priv);
 	dev->dev_private = NULL;

drivers/gpu/drm/nouveau/nv50_display.c

@@ -345,12 +345,15 @@ int nv50_display_create(struct drm_device *dev)
 void
 nv50_display_destroy(struct drm_device *dev)
 {
+	struct drm_nouveau_private *dev_priv = dev->dev_private;
+
 	NV_DEBUG_KMS(dev, "\n");
 
 	drm_mode_config_cleanup(dev);
 
 	nv50_display_disable(dev);
 	nouveau_irq_unregister(dev, 26);
+	flush_work_sync(&dev_priv->irq_work);
 }
 
 static u16
@@ -836,7 +839,7 @@ nv50_display_isr(struct drm_device *dev)
 		if (clock) {
 			nv_wr32(dev, NV03_PMC_INTR_EN_0, 0);
 			if (!work_pending(&dev_priv->irq_work))
-				queue_work(dev_priv->wq, &dev_priv->irq_work);
+				schedule_work(&dev_priv->irq_work);
 			delayed |= clock;
 			intr1 &= ~clock;
 		}

drivers/gpu/drm/nouveau/nv50_gpio.c

@@ -137,6 +137,7 @@ nv50_gpio_irq_unregister(struct drm_device *dev, enum dcb_gpio_tag tag,
 	struct nv50_gpio_priv *priv = pgpio->priv;
 	struct nv50_gpio_handler *gpioh, *tmp;
 	struct dcb_gpio_entry *gpio;
+	LIST_HEAD(tofree);
 	unsigned long flags;
 
 	gpio = nouveau_bios_gpio_entry(dev, tag);
@@ -149,10 +150,14 @@ nv50_gpio_irq_unregister(struct drm_device *dev, enum dcb_gpio_tag tag,
 		    gpioh->handler != handler ||
 		    gpioh->data != data)
 			continue;
-		list_del(&gpioh->head);
-		kfree(gpioh);
+		list_move(&gpioh->head, &tofree);
 	}
 	spin_unlock_irqrestore(&priv->lock, flags);
+
+	list_for_each_entry_safe(gpioh, tmp, &tofree, head) {
+		flush_work_sync(&gpioh->work);
+		kfree(gpioh);
+	}
 }
 
 bool
@@ -291,7 +296,7 @@ nv50_gpio_isr(struct drm_device *dev)
 			continue;
 		gpioh->inhibit = true;
 
-		queue_work(dev_priv->wq, &gpioh->work);
+		schedule_work(&gpioh->work);
 	}
 	spin_unlock(&priv->lock);
 }