drm/vkms: Add functions to map/unmap GEM backing storage

This patch add the necessary functions to map/unmap GEM
backing memory to the kernel's virtual address space.
Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/4b6563ae4f4337a5fd51f872424addf64e8d59a6.1532446182.git.hamohammed.sa@gmail.com

drivers/gpu/drm/vkms/vkms_drv.h

@@ -39,6 +39,8 @@ struct vkms_gem_object {
 	struct drm_gem_object gem;
 	struct mutex pages_lock; /* Page lock used in page fault handler */
 	struct page **pages;
+	unsigned int vmap_count;
+	void *vaddr;
 };
 
 #define drm_crtc_to_vkms_output(target) \
@@ -47,6 +49,9 @@ struct vkms_gem_object {
 #define drm_device_to_vkms_device(target) \
 	container_of(target, struct vkms_device, drm)
 
+#define drm_gem_to_vkms_gem(target)\
+	container_of(target, struct vkms_gem_object, gem)
+
 /* CRTC */
 int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
 		   struct drm_plane *primary, struct drm_plane *cursor);
@@ -75,4 +80,8 @@ int vkms_dumb_map(struct drm_file *file, struct drm_device *dev,
 
 void vkms_gem_free_object(struct drm_gem_object *obj);
 
+int vkms_gem_vmap(struct drm_gem_object *obj);
+
+void vkms_gem_vunmap(struct drm_gem_object *obj);
+
 #endif /* _VKMS_DRV_H_ */

drivers/gpu/drm/vkms/vkms_gem.c

@@ -37,7 +37,9 @@ void vkms_gem_free_object(struct drm_gem_object *obj)
 	struct vkms_gem_object *gem = container_of(obj, struct vkms_gem_object,
 						   gem);
 
-	kvfree(gem->pages);
+	WARN_ON(gem->pages);
+	WARN_ON(gem->vaddr);
+
 	mutex_destroy(&gem->pages_lock);
 	drm_gem_object_release(obj);
 	kfree(gem);
@@ -177,3 +179,78 @@ int vkms_dumb_map(struct drm_file *file, struct drm_device *dev,
 
 	return ret;
 }
+
+static struct page **_get_pages(struct vkms_gem_object *vkms_obj)
+{
+	struct drm_gem_object *gem_obj = &vkms_obj->gem;
+
+	if (!vkms_obj->pages) {
+		struct page **pages = drm_gem_get_pages(gem_obj);
+
+		if (IS_ERR(pages))
+			return pages;
+
+		if (cmpxchg(&vkms_obj->pages, NULL, pages))
+			drm_gem_put_pages(gem_obj, pages, false, true);
+	}
+
+	return vkms_obj->pages;
+}
+
+void vkms_gem_vunmap(struct drm_gem_object *obj)
+{
+	struct vkms_gem_object *vkms_obj = drm_gem_to_vkms_gem(obj);
+
+	mutex_lock(&vkms_obj->pages_lock);
+	if (vkms_obj->vmap_count < 1) {
+		WARN_ON(vkms_obj->vaddr);
+		WARN_ON(vkms_obj->pages);
+		mutex_unlock(&vkms_obj->pages_lock);
+		return;
+	}
+
+	vkms_obj->vmap_count--;
+
+	if (vkms_obj->vmap_count == 0) {
+		vunmap(vkms_obj->vaddr);
+		vkms_obj->vaddr = NULL;
+		drm_gem_put_pages(obj, vkms_obj->pages, false, true);
+		vkms_obj->pages = NULL;
+	}
+
+	mutex_unlock(&vkms_obj->pages_lock);
+}
+
+int vkms_gem_vmap(struct drm_gem_object *obj)
+{
+	struct vkms_gem_object *vkms_obj = drm_gem_to_vkms_gem(obj);
+	int ret = 0;
+
+	mutex_lock(&vkms_obj->pages_lock);
+
+	if (!vkms_obj->vaddr) {
+		unsigned int n_pages = obj->size >> PAGE_SHIFT;
+		struct page **pages = _get_pages(vkms_obj);
+
+		if (IS_ERR(pages)) {
+			ret = PTR_ERR(pages);
+			goto out;
+		}
+
+		vkms_obj->vaddr = vmap(pages, n_pages, VM_MAP, PAGE_KERNEL);
+		if (!vkms_obj->vaddr)
+			goto err_vmap;
+
+		vkms_obj->vmap_count++;
+	}
+
+	goto out;
+
+err_vmap:
+	ret = -ENOMEM;
+	drm_gem_put_pages(obj, vkms_obj->pages, false, true);
+	vkms_obj->pages = NULL;
+out:
+	mutex_unlock(&vkms_obj->pages_lock);
+	return ret;
+}