drm: document drm_auth.c

Also extract drm_auth.h for nicer grouping.

v2: Nuke the other comments since they don't really explain a lot, and
within the drm core we generally only document functions exported to
drivers: The main audience for these docs are driver writers.

v3: Limit the exposure of drm_master internals by only including
drm_auth.h where it is neede (Chris).

v4: Spelling polish (Emil).

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Documentation/gpu/drm-uapi.rst

@@ -20,6 +20,19 @@ libdrm Device Lookup
 .. kernel-doc:: drivers/gpu/drm/drm_ioctl.c
    :doc: getunique and setversion story
 
+
+Primary Nodes, DRM Master and Authentication
+============================================
+
+.. kernel-doc:: drivers/gpu/drm/drm_auth.c
+   :doc: master and authentication
+
+.. kernel-doc:: drivers/gpu/drm/drm_auth.c
+   :export:
+
+.. kernel-doc:: include/drm/drm_auth.h
+   :internal:
+
 Render nodes
 ============
 

drivers/gpu/drm/drm_auth.c

@@ -33,17 +33,27 @@
 #include "drm_legacy.h"
 
 /**
- * drm_getmagic - Get unique magic of a client
- * @dev: DRM device to operate on
- * @data: ioctl data containing the drm_auth object
- * @file_priv: DRM file that performs the operation
+ * DOC: master and authentication
  *
- * This looks up the unique magic of the passed client and returns it. If the
- * client did not have a magic assigned, yet, a new one is registered. The magic
- * is stored in the passed drm_auth object.
+ * struct &drm_master is used to track groups of clients with open
+ * primary/legacy device nodes. For every struct &drm_file which has had at
+ * least once successfully became the device master (either through the
+ * SET_MASTER IOCTL, or implicitly through opening the primary device node when
+ * no one else is the current master that time) there exists one &drm_master.
+ * This is noted in the is_master member of &drm_file. All other clients have
+ * just a pointer to the &drm_master they are associated with.
  *
- * Returns: 0 on success, negative error code on failure.
+ * In addition only one &drm_master can be the current master for a &drm_device.
+ * It can be switched through the DROP_MASTER and SET_MASTER IOCTL, or
+ * implicitly through closing/openeing the primary device node. See also
+ * drm_is_current_master().
+ *
+ * Clients can authenticate against the current master (if it matches their own)
+ * using the GETMAGIC and AUTHMAGIC IOCTLs. Together with exchanging masters,
+ * this allows controlled access to the device for an entire group of mutually
+ * trusted clients.
  */
+
 int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
 {
 	struct drm_auth *auth = data;
@@ -64,16 +74,6 @@ int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
 	return ret < 0 ? ret : 0;
 }
 
-/**
- * drm_authmagic - Authenticate client with a magic
- * @dev: DRM device to operate on
- * @data: ioctl data containing the drm_auth object
- * @file_priv: DRM file that performs the operation
- *
- * This looks up a DRM client by the passed magic and authenticates it.
- *
- * Returns: 0 on success, negative error code on failure.
- */
 int drm_authmagic(struct drm_device *dev, void *data,
 		  struct drm_file *file_priv)
 {
@@ -126,16 +126,6 @@ static int drm_set_master(struct drm_device *dev, struct drm_file *fpriv,
 	return ret;
 }
 
-/*
- * drm_new_set_master - Allocate a new master object and become master for the
- * associated master realm.
- *
- * @dev: The associated device.
- * @fpriv: File private identifying the client.
- *
- * This function must be called with dev::master_mutex held.
- * Returns negative error code on failure. Zero on success.
- */
 static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
 {
 	struct drm_master *old_master;
@@ -286,12 +276,28 @@ out:
 	mutex_unlock(&dev->master_mutex);
 }
 
+/**
+ * drm_is_current_master - checks whether @priv is the current master
+ * @fpriv: DRM file private
+ *
+ * Checks whether @fpriv is current master on its device. This decides whether a
+ * client is allowed to run DRM_MASTER IOCTLs.
+ *
+ * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting
+ * - the current master is assumed to own the non-shareable display hardware.
+ */
 bool drm_is_current_master(struct drm_file *fpriv)
 {
 	return fpriv->is_master && fpriv->master == fpriv->minor->dev->master;
 }
 EXPORT_SYMBOL(drm_is_current_master);
 
+/**
+ * drm_master_get - reference a master pointer
+ * @master: struct &drm_master
+ *
+ * Increments the reference count of @master and returns a pointer to @master.
+ */
 struct drm_master *drm_master_get(struct drm_master *master)
 {
 	kref_get(&master->refcount);
@@ -314,6 +320,12 @@ static void drm_master_destroy(struct kref *kref)
 	kfree(master);
 }
 
+/**
+ * drm_master_put - unreference and clear a master pointer
+ * @master: pointer to a pointer of struct &drm_master
+ *
+ * This decrements the &drm_master behind @master and sets it to NULL.
+ */
 void drm_master_put(struct drm_master **master)
 {
 	kref_put(&(*master)->refcount, drm_master_destroy);

drivers/gpu/drm/drm_crtc.c

@@ -39,6 +39,7 @@
 #include <drm/drm_fourcc.h>
 #include <drm/drm_modeset_lock.h>
 #include <drm/drm_atomic.h>
+#include <drm/drm_auth.h>
 
 #include "drm_crtc_internal.h"
 #include "drm_internal.h"

drivers/gpu/drm/drm_ioctl.c

@@ -30,6 +30,7 @@
 
 #include <drm/drmP.h>
 #include <drm/drm_core.h>
+#include <drm/drm_auth.h>
 #include "drm_legacy.h"
 #include "drm_internal.h"
 #include "drm_crtc_internal.h"

drivers/gpu/drm/i915/i915_drv.h

@@ -47,6 +47,7 @@
 #include <drm/intel-gtt.h>
 #include <drm/drm_legacy.h> /* for struct drm_dma_handle */
 #include <drm/drm_gem.h>
+#include <drm/drm_auth.h>
 
 #include "i915_params.h"
 #include "i915_reg.h"

drivers/gpu/drm/vmwgfx/vmwgfx_drv.h

@@ -32,6 +32,7 @@
 #include <drm/drmP.h>
 #include <drm/vmwgfx_drm.h>
 #include <drm/drm_hashtab.h>
+#include <drm/drm_auth.h>
 #include <linux/suspend.h>
 #include <drm/ttm/ttm_bo_driver.h>
 #include <drm/ttm/ttm_object.h>

include/drm/drmP.h

@@ -86,6 +86,7 @@ struct drm_local_map;
 struct drm_device_dma;
 struct drm_dma_handle;
 struct drm_gem_object;
+struct drm_master;
 
 struct device_node;
 struct videomode;
@@ -373,30 +374,6 @@ struct drm_lock_data {
 	int idle_has_lock;
 };
 
-/**
- * struct drm_master - drm master structure
- *
- * @refcount: Refcount for this master object.
- * @dev: Link back to the DRM device
- * @unique: Unique identifier: e.g. busid. Protected by drm_global_mutex.
- * @unique_len: Length of unique field. Protected by drm_global_mutex.
- * @magic_map: Map of used authentication tokens. Protected by struct_mutex.
- * @lock: DRI lock information.
- * @driver_priv: Pointer to driver-private information.
- *
- * Note that master structures are only relevant for the legacy/primary device
- * nodes, hence there can only be one per device, not one per drm_minor.
- */
-struct drm_master {
-	struct kref refcount;
-	struct drm_device *dev;
-	char *unique;
-	int unique_len;
-	struct idr magic_map;
-	struct drm_lock_data lock;
-	void *driver_priv;
-};
-
 /* Flags and return codes for get_vblank_timestamp() driver function. */
 #define DRM_CALLED_FROM_VBLIRQ 1
 #define DRM_VBLANKTIME_SCANOUTPOS_METHOD (1 << 0)
@@ -1012,11 +989,6 @@ static inline wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc
 extern void drm_vblank_pre_modeset(struct drm_device *dev, unsigned int pipe);
 extern void drm_vblank_post_modeset(struct drm_device *dev, unsigned int pipe);
 
-/* drm_auth.c */
-struct drm_master *drm_master_get(struct drm_master *master);
-void drm_master_put(struct drm_master **master);
-bool drm_is_current_master(struct drm_file *fpriv);
-
 /* drm_drv.c */
 void drm_put_dev(struct drm_device *dev);
 void drm_unplug_dev(struct drm_device *dev);

include/drm/drm_auth.h

@@ -0,0 +1,59 @@
+/*
+ * Internal Header for the Direct Rendering Manager
+ *
+ * Copyright 2016 Intel Corporation
+ *
+ * Author: Daniel Vetter <daniel.vetter@ffwll.ch>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * VA LINUX SYSTEMS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef _DRM_AUTH_H_
+#define _DRM_AUTH_H_
+
+/**
+ * struct drm_master - drm master structure
+ *
+ * @refcount: Refcount for this master object.
+ * @dev: Link back to the DRM device
+ * @unique: Unique identifier: e.g. busid. Protected by drm_global_mutex.
+ * @unique_len: Length of unique field. Protected by drm_global_mutex.
+ * @magic_map: Map of used authentication tokens. Protected by struct_mutex.
+ * @lock: DRI lock information.
+ * @driver_priv: Pointer to driver-private information.
+ *
+ * Note that master structures are only relevant for the legacy/primary device
+ * nodes, hence there can only be one per device, not one per drm_minor.
+ */
+struct drm_master {
+	struct kref refcount;
+	struct drm_device *dev;
+	char *unique;
+	int unique_len;
+	struct idr magic_map;
+	struct drm_lock_data lock;
+	void *driver_priv;
+};
+
+struct drm_master *drm_master_get(struct drm_master *master);
+void drm_master_put(struct drm_master **master);
+bool drm_is_current_master(struct drm_file *fpriv);
+
+#endif

include/drm/drm_legacy.h

@@ -1,6 +1,8 @@
 #ifndef __DRM_DRM_LEGACY_H__
 #define __DRM_DRM_LEGACY_H__
 
+#include <drm/drm_auth.h>
+
 /*
  * Legacy driver interfaces for the Direct Rendering Manager
  *