drm: add mmap() to drm_gem_object_funcs

drm_gem_object_funcs->vm_ops alone can't handle everything which needs
to be done for mmap(), tweaking vm_flags for example.  So add a new
mmap() callback to drm_gem_object_funcs where this code can go to.

Note that the vm_ops field is not used in case the mmap callback is
present, it is expected that the callback sets vma->vm_ops instead.

Also setting vm_flags and vm_page_prot is the job of the new callback.
so drivers have more control over these flags.

drm_gem_mmap_obj() will use the new callback for object specific mmap
setup.  With this in place the need for driver-speific fops->mmap
callbacks goes away, drm_gem_mmap can be hooked instead.

drm_gem_prime_mmap() will use the new callback too to just mmap gem
objects directly instead of jumping though loops to make
drm_gem_object_lookup() and fops->mmap work.
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20191016115203.20095-2-kraxel@redhat.com

drivers/gpu/drm/drm_gem.c

@@ -1099,22 +1099,31 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size,
 		     struct vm_area_struct *vma)
 {
 	struct drm_device *dev = obj->dev;
+	int ret;
 
 	/* Check for valid size. */
 	if (obj_size < vma->vm_end - vma->vm_start)
 		return -EINVAL;
 
-	if (obj->funcs && obj->funcs->vm_ops)
-		vma->vm_ops = obj->funcs->vm_ops;
-	else if (dev->driver->gem_vm_ops)
-		vma->vm_ops = dev->driver->gem_vm_ops;
-	else
-		return -EINVAL;
+	if (obj->funcs && obj->funcs->mmap) {
+		ret = obj->funcs->mmap(obj, vma);
+		if (ret)
+			return ret;
+		WARN_ON(!(vma->vm_flags & VM_DONTEXPAND));
+	} else {
+		if (obj->funcs && obj->funcs->vm_ops)
+			vma->vm_ops = obj->funcs->vm_ops;
+		else if (dev->driver->gem_vm_ops)
+			vma->vm_ops = dev->driver->gem_vm_ops;
+		else
+			return -EINVAL;
+
+		vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
+		vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
+		vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
+	}
 
-	vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;
 	vma->vm_private_data = obj;
-	vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
-	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
 
 	/* Take a ref for this mapping of the object, so that the fault
 	 * handler can dereference the mmap offset's pointer to the object.

drivers/gpu/drm/drm_prime.c

@@ -713,6 +713,15 @@ int drm_gem_prime_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
 	struct file *fil;
 	int ret;
 
+	if (obj->funcs && obj->funcs->mmap) {
+		ret = obj->funcs->mmap(obj, vma);
+		if (ret)
+			return ret;
+		vma->vm_private_data = obj;
+		drm_gem_object_get(obj);
+		return 0;
+	}
+
 	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 	fil = kzalloc(sizeof(*fil), GFP_KERNEL);
 	if (!priv || !fil) {

include/drm/drm_gem.h

@@ -150,6 +150,20 @@ struct drm_gem_object_funcs {
 	 */
 	void (*vunmap)(struct drm_gem_object *obj, void *vaddr);
 
+	/**
+	 * @mmap:
+	 *
+	 * Handle mmap() of the gem object, setup vma accordingly.
+	 *
+	 * This callback is optional.
+	 *
+	 * The callback is used by by both drm_gem_mmap_obj() and
+	 * drm_gem_prime_mmap().  When @mmap is present @vm_ops is not
+	 * used, the @mmap callback must set vma->vm_ops instead.
+	 *
+	 */
+	int (*mmap)(struct drm_gem_object *obj, struct vm_area_struct *vma);
+
 	/**
 	 * @vm_ops:
 	 *