Merge tag 'drm/gem-cma/for-3.19-rc1' of git://people.freedesktop.org/~tagr/linux into drm-next

drm: Sanitize DRM_IOCTL_MODE_CREATE_DUMB input

Some drivers erroneously treat the .pitch and .size fields of struct
drm_mode_create_dumb as inputs. While the include/uapi/drm/drm_mode.h
header has a comment denoting them as outputs, that seemingly wasn't
enough to make drivers use them properly.

The result is that some userspace doesn't explicitly zero out those
fields, assuming that the kernel won't use them. That causes problems
since the data within the structure might be uninitialized, so bogus
data may end up confusing drivers (ridiculously large values for the
pitch, ...).

This series attempts to improve the situation by fixing all drivers to
not use the output fields. Furthermore to spare new drivers this bad
surprise, the DRM core now zeros out these fields prior to handing the
data structure to the driver.

Lessons learned from this are that future IOCTLs should be properly
documented (in the DRM DocBook for example) and should be rigorously
defined. To prevent misuse like this, userspace should be required to
zero out all output fields. The kernel should check for this and fail
if that's not the case.

* tag 'drm/gem-cma/for-3.19-rc1' of git://people.freedesktop.org/~tagr/linux:
  drm/cma: Remove call to drm_gem_free_mmap_offset()
  drm: Sanitize DRM_IOCTL_MODE_CREATE_DUMB input
  drm/rcar: gem: dumb: pitch is an output
  drm/omap: gem: dumb: pitch is an output
  drm/cma: Introduce drm_gem_cma_dumb_create_internal()
  drm/doc: Add GEM/CMA helpers to kerneldoc
  drm/doc: mm: Fix indentation
  drm/gem: Fix a few kerneldoc typos

7 files changed, 395 insertions, 196 deletions

diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
index b8bfa8d1f289..8c54f9a393cf 100644
--- a/Documentation/DocBook/drm.tmpl
+++ b/Documentation/DocBook/drm.tmpl
@@ -492,10 +492,10 @@ char *date;</synopsis>
     <sect2>
       <title>The Translation Table Manager (TTM)</title>
       <para>
-	TTM design background and information belongs here.
+        TTM design background and information belongs here.
       </para>
       <sect3>
-	<title>TTM initialization</title>
+        <title>TTM initialization</title>
         <warning><para>This section is outdated.</para></warning>
         <para>
           Drivers wishing to support TTM must fill out a drm_bo_driver
@@ -503,42 +503,42 @@ char *date;</synopsis>
           pointers for initializing the TTM, allocating and freeing memory,
           waiting for command completion and fence synchronization, and memory
           migration. See the radeon_ttm.c file for an example of usage.
-	</para>
-	<para>
-	  The ttm_global_reference structure is made up of several fields:
-	</para>
-	<programlisting>
-	  struct ttm_global_reference {
-	  	enum ttm_global_types global_type;
-	  	size_t size;
-	  	void *object;
-	  	int (*init) (struct ttm_global_reference *);
-	  	void (*release) (struct ttm_global_reference *);
-	  };
-	</programlisting>
-	<para>
-	  There should be one global reference structure for your memory
-	  manager as a whole, and there will be others for each object
-	  created by the memory manager at runtime.  Your global TTM should
-	  have a type of TTM_GLOBAL_TTM_MEM.  The size field for the global
-	  object should be sizeof(struct ttm_mem_global), and the init and
-	  release hooks should point at your driver-specific init and
-	  release routines, which probably eventually call
-	  ttm_mem_global_init and ttm_mem_global_release, respectively.
-	</para>
-	<para>
-	  Once your global TTM accounting structure is set up and initialized
-	  by calling ttm_global_item_ref() on it,
-	  you need to create a buffer object TTM to
-	  provide a pool for buffer object allocation by clients and the
-	  kernel itself.  The type of this object should be TTM_GLOBAL_TTM_BO,
-	  and its size should be sizeof(struct ttm_bo_global).  Again,
-	  driver-specific init and release functions may be provided,
-	  likely eventually calling ttm_bo_global_init() and
-	  ttm_bo_global_release(), respectively.  Also, like the previous
-	  object, ttm_global_item_ref() is used to create an initial reference
-	  count for the TTM, which will call your initialization function.
-	</para>
+        </para>
+        <para>
+          The ttm_global_reference structure is made up of several fields:
+        </para>
+        <programlisting>
+          struct ttm_global_reference {
+                  enum ttm_global_types global_type;
+                  size_t size;
+                  void *object;
+                  int (*init) (struct ttm_global_reference *);
+                  void (*release) (struct ttm_global_reference *);
+          };
+        </programlisting>
+        <para>
+          There should be one global reference structure for your memory
+          manager as a whole, and there will be others for each object
+          created by the memory manager at runtime.  Your global TTM should
+          have a type of TTM_GLOBAL_TTM_MEM.  The size field for the global
+          object should be sizeof(struct ttm_mem_global), and the init and
+          release hooks should point at your driver-specific init and
+          release routines, which probably eventually call
+          ttm_mem_global_init and ttm_mem_global_release, respectively.
+        </para>
+        <para>
+          Once your global TTM accounting structure is set up and initialized
+          by calling ttm_global_item_ref() on it,
+          you need to create a buffer object TTM to
+          provide a pool for buffer object allocation by clients and the
+          kernel itself.  The type of this object should be TTM_GLOBAL_TTM_BO,
+          and its size should be sizeof(struct ttm_bo_global).  Again,
+          driver-specific init and release functions may be provided,
+          likely eventually calling ttm_bo_global_init() and
+          ttm_bo_global_release(), respectively.  Also, like the previous
+          object, ttm_global_item_ref() is used to create an initial reference
+          count for the TTM, which will call your initialization function.
+        </para>
       </sect3>
     </sect2>
     <sect2 id="drm-gem">
@@ -566,19 +566,19 @@ char *date;</synopsis>
         using driver-specific ioctls.
       </para>
       <para>
-	On a fundamental level, GEM involves several operations:
-	<itemizedlist>
-	  <listitem>Memory allocation and freeing</listitem>
-	  <listitem>Command execution</listitem>
-	  <listitem>Aperture management at command execution time</listitem>
-	</itemizedlist>
-	Buffer object allocation is relatively straightforward and largely
+        On a fundamental level, GEM involves several operations:
+        <itemizedlist>
+          <listitem>Memory allocation and freeing</listitem>
+          <listitem>Command execution</listitem>
+          <listitem>Aperture management at command execution time</listitem>
+        </itemizedlist>
+        Buffer object allocation is relatively straightforward and largely
         provided by Linux's shmem layer, which provides memory to back each
         object.
       </para>
       <para>
         Device-specific operations, such as command execution, pinning, buffer
-	read &amp; write, mapping, and domain ownership transfers are left to
+        read &amp; write, mapping, and domain ownership transfers are left to
         driver-specific ioctls.
       </para>
       <sect3>
@@ -738,16 +738,16 @@ char *date;</synopsis>
           respectively. The conversion is handled by the DRM core without any
           driver-specific support.
         </para>
-	<para>
-	  GEM also supports buffer sharing with dma-buf file descriptors through
-	  PRIME. GEM-based drivers must use the provided helpers functions to
-	  implement the exporting and importing correctly. See <xref linkend="drm-prime-support" />.
-	  Since sharing file descriptors is inherently more secure than the
-	  easily guessable and global GEM names it is the preferred buffer
-	  sharing mechanism. Sharing buffers through GEM names is only supported
-	  for legacy userspace. Furthermore PRIME also allows cross-device
-	  buffer sharing since it is based on dma-bufs.
-	</para>
+        <para>
+          GEM also supports buffer sharing with dma-buf file descriptors through
+          PRIME. GEM-based drivers must use the provided helpers functions to
+          implement the exporting and importing correctly. See <xref linkend="drm-prime-support" />.
+          Since sharing file descriptors is inherently more secure than the
+          easily guessable and global GEM names it is the preferred buffer
+          sharing mechanism. Sharing buffers through GEM names is only supported
+          for legacy userspace. Furthermore PRIME also allows cross-device
+          buffer sharing since it is based on dma-bufs.
+        </para>
       </sect3>
       <sect3 id="drm-gem-objects-mapping">
         <title>GEM Objects Mapping</title>
@@ -852,7 +852,7 @@ char *date;</synopsis>
       <sect3>
         <title>Command Execution</title>
         <para>
-	  Perhaps the most important GEM function for GPU devices is providing a
+          Perhaps the most important GEM function for GPU devices is providing a
           command execution interface to clients. Client programs construct
           command buffers containing references to previously allocated memory
           objects, and then submit them to GEM. At that point, GEM takes care to
@@ -874,95 +874,101 @@ char *date;</synopsis>
         <title>GEM Function Reference</title>
 !Edrivers/gpu/drm/drm_gem.c
       </sect3>
-      </sect2>
-      <sect2>
-	<title>VMA Offset Manager</title>
+    </sect2>
+    <sect2>
+      <title>VMA Offset Manager</title>
 !Pdrivers/gpu/drm/drm_vma_manager.c vma offset manager
 !Edrivers/gpu/drm/drm_vma_manager.c
 !Iinclude/drm/drm_vma_manager.h
-      </sect2>
-      <sect2 id="drm-prime-support">
-	<title>PRIME Buffer Sharing</title>
-	<para>
-	  PRIME is the cross device buffer sharing framework in drm, originally
-	  created for the OPTIMUS range of multi-gpu platforms. To userspace
-	  PRIME buffers are dma-buf based file descriptors.
-	</para>
-	<sect3>
-	  <title>Overview and Driver Interface</title>
-	  <para>
-	    Similar to GEM global names, PRIME file descriptors are
-	    also used to share buffer objects across processes. They offer
-	    additional security: as file descriptors must be explicitly sent over
-	    UNIX domain sockets to be shared between applications, they can't be
-	    guessed like the globally unique GEM names.
-	  </para>
-	  <para>
-	    Drivers that support the PRIME
-	    API must set the DRIVER_PRIME bit in the struct
-	    <structname>drm_driver</structname>
-	    <structfield>driver_features</structfield> field, and implement the
-	    <methodname>prime_handle_to_fd</methodname> and
-	    <methodname>prime_fd_to_handle</methodname> operations.
-	  </para>
-	  <para>
-	    <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
-			  struct drm_file *file_priv, uint32_t handle,
-			  uint32_t flags, int *prime_fd);
+    </sect2>
+    <sect2 id="drm-prime-support">
+      <title>PRIME Buffer Sharing</title>
+      <para>
+        PRIME is the cross device buffer sharing framework in drm, originally
+        created for the OPTIMUS range of multi-gpu platforms. To userspace
+        PRIME buffers are dma-buf based file descriptors.
+      </para>
+      <sect3>
+        <title>Overview and Driver Interface</title>
+        <para>
+          Similar to GEM global names, PRIME file descriptors are
+          also used to share buffer objects across processes. They offer
+          additional security: as file descriptors must be explicitly sent over
+          UNIX domain sockets to be shared between applications, they can't be
+          guessed like the globally unique GEM names.
+        </para>
+        <para>
+          Drivers that support the PRIME
+          API must set the DRIVER_PRIME bit in the struct
+          <structname>drm_driver</structname>
+          <structfield>driver_features</structfield> field, and implement the
+          <methodname>prime_handle_to_fd</methodname> and
+          <methodname>prime_fd_to_handle</methodname> operations.
+        </para>
+        <para>
+          <synopsis>int (*prime_handle_to_fd)(struct drm_device *dev,
+                          struct drm_file *file_priv, uint32_t handle,
+                          uint32_t flags, int *prime_fd);
 int (*prime_fd_to_handle)(struct drm_device *dev,
-			  struct drm_file *file_priv, int prime_fd,
-			  uint32_t *handle);</synopsis>
-	    Those two operations convert a handle to a PRIME file descriptor and
-	    vice versa. Drivers must use the kernel dma-buf buffer sharing framework
-	    to manage the PRIME file descriptors. Similar to the mode setting
-	    API PRIME is agnostic to the underlying buffer object manager, as
-	    long as handles are 32bit unsigned integers.
-	  </para>
-	  <para>
-	    While non-GEM drivers must implement the operations themselves, GEM
-	    drivers must use the <function>drm_gem_prime_handle_to_fd</function>
-	    and <function>drm_gem_prime_fd_to_handle</function> helper functions.
-	    Those helpers rely on the driver
-	    <methodname>gem_prime_export</methodname> and
-	    <methodname>gem_prime_import</methodname> operations to create a dma-buf
-	    instance from a GEM object (dma-buf exporter role) and to create a GEM
-	    object from a dma-buf instance (dma-buf importer role).
-	  </para>
-	  <para>
-	    <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
-				     struct drm_gem_object *obj,
-				     int flags);
+                          struct drm_file *file_priv, int prime_fd,
+                          uint32_t *handle);</synopsis>
+            Those two operations convert a handle to a PRIME file descriptor and
+            vice versa. Drivers must use the kernel dma-buf buffer sharing framework
+            to manage the PRIME file descriptors. Similar to the mode setting
+            API PRIME is agnostic to the underlying buffer object manager, as
+            long as handles are 32bit unsigned integers.
+          </para>
+          <para>
+            While non-GEM drivers must implement the operations themselves, GEM
+            drivers must use the <function>drm_gem_prime_handle_to_fd</function>
+            and <function>drm_gem_prime_fd_to_handle</function> helper functions.
+            Those helpers rely on the driver
+            <methodname>gem_prime_export</methodname> and
+            <methodname>gem_prime_import</methodname> operations to create a dma-buf
+            instance from a GEM object (dma-buf exporter role) and to create a GEM
+            object from a dma-buf instance (dma-buf importer role).
+          </para>
+          <para>
+            <synopsis>struct dma_buf * (*gem_prime_export)(struct drm_device *dev,
+                             struct drm_gem_object *obj,
+                             int flags);
 struct drm_gem_object * (*gem_prime_import)(struct drm_device *dev,
-					    struct dma_buf *dma_buf);</synopsis>
-	    These two operations are mandatory for GEM drivers that support
-	    PRIME.
-	  </para>
-	</sect3>
-        <sect3>
-          <title>PRIME Helper Functions</title>
-!Pdrivers/gpu/drm/drm_prime.c PRIME Helpers
+                                            struct dma_buf *dma_buf);</synopsis>
+            These two operations are mandatory for GEM drivers that support
+            PRIME.
+          </para>
         </sect3>
-      </sect2>
-      <sect2>
-	<title>PRIME Function References</title>
+      <sect3>
+        <title>PRIME Helper Functions</title>
+!Pdrivers/gpu/drm/drm_prime.c PRIME Helpers
+      </sect3>
+    </sect2>
+    <sect2>
+      <title>PRIME Function References</title>
 !Edrivers/gpu/drm/drm_prime.c
-      </sect2>
-      <sect2>
-	<title>DRM MM Range Allocator</title>
-	<sect3>
-	  <title>Overview</title>
+    </sect2>
+    <sect2>
+      <title>DRM MM Range Allocator</title>
+      <sect3>
+        <title>Overview</title>
 !Pdrivers/gpu/drm/drm_mm.c Overview
-	</sect3>
-	<sect3>
-	  <title>LRU Scan/Eviction Support</title>
+      </sect3>
+      <sect3>
+        <title>LRU Scan/Eviction Support</title>
 !Pdrivers/gpu/drm/drm_mm.c lru scan roaster
-	</sect3>
+      </sect3>
       </sect2>
-      <sect2>
-	<title>DRM MM Range Allocator Function References</title>
+    <sect2>
+      <title>DRM MM Range Allocator Function References</title>
 !Edrivers/gpu/drm/drm_mm.c
 !Iinclude/drm/drm_mm.h
-      </sect2>
+    </sect2>
+    <sect2>
+      <title>CMA Helper Functions Reference</title>
+!Pdrivers/gpu/drm/drm_gem_cma_helper.c cma helpers
+!Edrivers/gpu/drm/drm_gem_cma_helper.c
+!Iinclude/drm/drm_gem_cma_helper.h
+    </sect2>
   </sect1>
 
   <!-- Internals: mode setting -->
diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 15f8b3bfd1ee..56737e74b59d 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -4774,6 +4774,16 @@ int drm_mode_create_dumb_ioctl(struct drm_device *dev,
 	if (PAGE_ALIGN(size) == 0)
 		return -EINVAL;
 
+	/*
+	 * handle, pitch and size are output parameters. Zero them out to
+	 * prevent drivers from accidentally using uninitialized data. Since
+	 * not all existing userspace is clearing these fields properly we
+	 * cannot reject IOCTL with garbage in them.
+	 */
+	args->handle = 0;
+	args->pitch = 0;
+	args->size = 0;
+
 	return dev->driver->dumb_create(file_priv, dev, args);
 }
 
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
index 973a9b6644d4..16a164770713 100644
--- a/drivers/gpu/drm/drm_gem.c
+++ b/drivers/gpu/drm/drm_gem.c
@@ -309,7 +309,7 @@ EXPORT_SYMBOL(drm_gem_dumb_destroy);
  * drm_gem_handle_create_tail - internal functions to create a handle
  * @file_priv: drm file-private structure to register the handle for
  * @obj: object to register
- * @handlep: pionter to return the created handle to the caller
+ * @handlep: pointer to return the created handle to the caller
  * 
  * This expects the dev->object_name_lock to be held already and will drop it
  * before returning. Used to avoid races in establishing new handles when
@@ -362,7 +362,7 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
 }
 
 /**
- * gem_handle_create - create a gem handle for an object
+ * drm_gem_handle_create - create a gem handle for an object
  * @file_priv: drm file-private structure to register the handle for
  * @obj: object to register
  * @handlep: pionter to return the created handle to the caller
@@ -371,10 +371,9 @@ drm_gem_handle_create_tail(struct drm_file *file_priv,
  * to the object, which includes a regular reference count. Callers
  * will likely want to dereference the object afterwards.
  */
-int
-drm_gem_handle_create(struct drm_file *file_priv,
-		       struct drm_gem_object *obj,
-		       u32 *handlep)
+int drm_gem_handle_create(struct drm_file *file_priv,
+			  struct drm_gem_object *obj,
+			  u32 *handlep)
 {
 	mutex_lock(&obj->dev->object_name_lock);
 
diff --git a/drivers/gpu/drm/drm_gem_cma_helper.c b/drivers/gpu/drm/drm_gem_cma_helper.c
index 0316310e2cc4..e419eedf751d 100644
--- a/drivers/gpu/drm/drm_gem_cma_helper.c
+++ b/drivers/gpu/drm/drm_gem_cma_helper.c
@@ -29,18 +29,31 @@
 #include <drm/drm_gem_cma_helper.h>
 #include <drm/drm_vma_manager.h>
 
-/*
+/**
+ * DOC: cma helpers
+ *
+ * The Contiguous Memory Allocator reserves a pool of memory at early boot
+ * that is used to service requests for large blocks of contiguous memory.
+ *
+ * The DRM GEM/CMA helpers use this allocator as a means to provide buffer
+ * objects that are physically contiguous in memory. This is useful for
+ * display drivers that are unable to map scattered buffers via an IOMMU.
+ */
+
+/**
  * __drm_gem_cma_create - Create a GEM CMA object without allocating memory
- * @drm: The drm device
- * @size: The GEM object size
+ * @drm: DRM device
+ * @size: size of the object to allocate
  *
- * This function creates and initializes a GEM CMA object of the given size, but
- * doesn't allocate any memory to back the object.
+ * This function creates and initializes a GEM CMA object of the given size,
+ * but doesn't allocate any memory to back the object.
  *
- * Return a struct drm_gem_cma_object* on success or ERR_PTR values on failure.
+ * Returns:
+ * A struct drm_gem_cma_object * on success or an ERR_PTR()-encoded negative
+ * error code on failure.
  */
 static struct drm_gem_cma_object *
-__drm_gem_cma_create(struct drm_device *drm, unsigned int size)
+__drm_gem_cma_create(struct drm_device *drm, size_t size)
 {
 	struct drm_gem_cma_object *cma_obj;
 	struct drm_gem_object *gem_obj;
@@ -69,14 +82,21 @@ error:
 	return ERR_PTR(ret);
 }
 
-/*
+/**
  * drm_gem_cma_create - allocate an object with the given size
+ * @drm: DRM device
+ * @size: size of the object to allocate
+ *
+ * This function creates a CMA GEM object and allocates a contiguous chunk of
+ * memory as backing store. The backing memory has the writecombine attribute
+ * set.
  *
- * returns a struct drm_gem_cma_object* on success or ERR_PTR values
- * on failure.
+ * Returns:
+ * A struct drm_gem_cma_object * on success or an ERR_PTR()-encoded negative
+ * error code on failure.
  */
 struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm,
-		unsigned int size)
+					      size_t size)
 {
 	struct drm_gem_cma_object *cma_obj;
 	int ret;
@@ -104,17 +124,26 @@ error:
 }
 EXPORT_SYMBOL_GPL(drm_gem_cma_create);
 
-/*
- * drm_gem_cma_create_with_handle - allocate an object with the given
- * size and create a gem handle on it
+/**
+ * drm_gem_cma_create_with_handle - allocate an object with the given size and
+ *     return a GEM handle to it
+ * @file_priv: DRM file-private structure to register the handle for
+ * @drm: DRM device
+ * @size: size of the object to allocate
+ * @handle: return location for the GEM handle
+ *
+ * This function creates a CMA GEM object, allocating a physically contiguous
+ * chunk of memory as backing store. The GEM object is then added to the list
+ * of object associated with the given file and a handle to it is returned.
  *
- * returns a struct drm_gem_cma_object* on success or ERR_PTR values
- * on failure.
+ * Returns:
+ * A struct drm_gem_cma_object * on success or an ERR_PTR()-encoded negative
+ * error code on failure.
  */
-static struct drm_gem_cma_object *drm_gem_cma_create_with_handle(
-		struct drm_file *file_priv,
-		struct drm_device *drm, unsigned int size,
-		unsigned int *handle)
+static struct drm_gem_cma_object *
+drm_gem_cma_create_with_handle(struct drm_file *file_priv,
+			       struct drm_device *drm, size_t size,
+			       uint32_t *handle)
 {
 	struct drm_gem_cma_object *cma_obj;
 	struct drm_gem_object *gem_obj;
@@ -145,16 +174,19 @@ err_handle_create:
 	return ERR_PTR(ret);
 }
 
-/*
- * drm_gem_cma_free_object - (struct drm_driver)->gem_free_object callback
- * function
+/**
+ * drm_gem_cma_free_object - free resources associated with a CMA GEM object
+ * @gem_obj: GEM object to free
+ *
+ * This function frees the backing memory of the CMA GEM object, cleans up the
+ * GEM object state and frees the memory used to store the object itself.
+ * Drivers using the CMA helpers should set this as their DRM driver's
+ * ->gem_free_object() callback.
  */
 void drm_gem_cma_free_object(struct drm_gem_object *gem_obj)
 {
 	struct drm_gem_cma_object *cma_obj;
 
-	drm_gem_free_mmap_offset(gem_obj);
-
 	cma_obj = to_drm_gem_cma_obj(gem_obj);
 
 	if (cma_obj->vaddr) {
@@ -170,18 +202,26 @@ void drm_gem_cma_free_object(struct drm_gem_object *gem_obj)
 }
 EXPORT_SYMBOL_GPL(drm_gem_cma_free_object);
 
-/*
- * drm_gem_cma_dumb_create - (struct drm_driver)->dumb_create callback
- * function
+/**
+ * drm_gem_cma_dumb_create_internal - create a dumb buffer object
+ * @file_priv: DRM file-private structure to create the dumb buffer for
+ * @drm: DRM device
+ * @args: IOCTL data
+ *
+ * This aligns the pitch and size arguments to the minimum required. This is
+ * an internal helper that can be wrapped by a driver to account for hardware
+ * with more specific alignment requirements. It should not be used directly
+ * as the ->dumb_create() callback in a DRM driver.
  *
- * This aligns the pitch and size arguments to the minimum required. wrap
- * this into your own function if you need bigger alignment.
+ * Returns:
+ * 0 on success or a negative error code on failure.
  */
-int drm_gem_cma_dumb_create(struct drm_file *file_priv,
-		struct drm_device *dev, struct drm_mode_create_dumb *args)
+int drm_gem_cma_dumb_create_internal(struct drm_file *file_priv,
+				     struct drm_device *drm,
+				     struct drm_mode_create_dumb *args)
 {
+	unsigned int min_pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
 	struct drm_gem_cma_object *cma_obj;
-	int min_pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
 
 	if (args->pitch < min_pitch)
 		args->pitch = min_pitch;
@@ -189,18 +229,63 @@ int drm_gem_cma_dumb_create(struct drm_file *file_priv,
 	if (args->size < args->pitch * args->height)
 		args->size = args->pitch * args->height;
 
-	cma_obj = drm_gem_cma_create_with_handle(file_priv, dev,
-			args->size, &args->handle);
+	cma_obj = drm_gem_cma_create_with_handle(file_priv, drm, args->size,
+						 &args->handle);
+	return PTR_ERR_OR_ZERO(cma_obj);
+}
+EXPORT_SYMBOL_GPL(drm_gem_cma_dumb_create_internal);
+
+/**
+ * drm_gem_cma_dumb_create - create a dumb buffer object
+ * @file_priv: DRM file-private structure to create the dumb buffer for
+ * @drm: DRM device
+ * @args: IOCTL data
+ *
+ * This function computes the pitch of the dumb buffer and rounds it up to an
+ * integer number of bytes per pixel. Drivers for hardware that doesn't have
+ * any additional restrictions on the pitch can directly use this function as
+ * their ->dumb_create() callback.
+ *
+ * For hardware with additional restrictions, drivers can adjust the fields
+ * set up by userspace and pass the IOCTL data along to the
+ * drm_gem_cma_dumb_create_internal() function.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
+ */
+int drm_gem_cma_dumb_create(struct drm_file *file_priv,
+			    struct drm_device *drm,
+			    struct drm_mode_create_dumb *args)
+{
+	struct drm_gem_cma_object *cma_obj;
+
+	args->pitch = DIV_ROUND_UP(args->width * args->bpp, 8);
+	args->size = args->pitch * args->height;
+
+	cma_obj = drm_gem_cma_create_with_handle(file_priv, drm, args->size,
+						 &args->handle);
 	return PTR_ERR_OR_ZERO(cma_obj);
 }
 EXPORT_SYMBOL_GPL(drm_gem_cma_dumb_create);
 
-/*
- * drm_gem_cma_dumb_map_offset - (struct drm_driver)->dumb_map_offset callback
- * function
+/**
+ * drm_gem_cma_dumb_map_offset - return the fake mmap offset for a CMA GEM
+ *     object
+ * @file_priv: DRM file-private structure containing the GEM object
+ * @drm: DRM device
+ * @handle: GEM object handle
+ * @offset: return location for the fake mmap offset
+ *
+ * This function look up an object by its handle and returns the fake mmap
+ * offset associated with it. Drivers using the CMA helpers should set this
+ * as their DRM driver's ->dumb_map_offset() callback.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
  */
 int drm_gem_cma_dumb_map_offset(struct drm_file *file_priv,
-		struct drm_device *drm, uint32_t handle, uint64_t *offset)
+				struct drm_device *drm, u32 handle,
+				u64 *offset)
 {
 	struct drm_gem_object *gem_obj;
 
@@ -208,7 +293,7 @@ int drm_gem_cma_dumb_map_offset(struct drm_file *file_priv,
 
 	gem_obj = drm_gem_object_lookup(drm, file_priv, handle);
 	if (!gem_obj) {
-		dev_err(drm->dev, "failed to lookup gem object\n");
+		dev_err(drm->dev, "failed to lookup GEM object\n");
 		mutex_unlock(&drm->struct_mutex);
 		return -EINVAL;
 	}
@@ -251,8 +336,20 @@ static int drm_gem_cma_mmap_obj(struct drm_gem_cma_object *cma_obj,
 	return ret;
 }
 
-/*
- * drm_gem_cma_mmap - (struct file_operation)->mmap callback function
+/**
+ * drm_gem_cma_mmap - memory-map a CMA GEM object
+ * @filp: file object
+ * @vma: VMA for the area to be mapped
+ *
+ * This function implements an augmented version of the GEM DRM file mmap
+ * operation for CMA objects: In addition to the usual GEM VMA setup it
+ * immediately faults in the entire object instead of using on-demaind
+ * faulting. Drivers which employ the CMA helpers should use this function
+ * as their ->mmap() handler in the DRM device file's file_operations
+ * structure.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
  */
 int drm_gem_cma_mmap(struct file *filp, struct vm_area_struct *vma)
 {
@@ -272,7 +369,16 @@ int drm_gem_cma_mmap(struct file *filp, struct vm_area_struct *vma)
 EXPORT_SYMBOL_GPL(drm_gem_cma_mmap);
 
 #ifdef CONFIG_DEBUG_FS
-void drm_gem_cma_describe(struct drm_gem_cma_object *cma_obj, struct seq_file *m)
+/**
+ * drm_gem_cma_describe - describe a CMA GEM object for debugfs
+ * @cma_obj: CMA GEM object
+ * @m: debugfs file handle
+ *
+ * This function can be used to dump a human-readable representation of the
+ * CMA GEM object into a synthetic file.
+ */
+void drm_gem_cma_describe(struct drm_gem_cma_object *cma_obj,
+			  struct seq_file *m)
 {
 	struct drm_gem_object *obj = &cma_obj->base;
 	struct drm_device *dev = obj->dev;
@@ -291,7 +397,18 @@ void drm_gem_cma_describe(struct drm_gem_cma_object *cma_obj, struct seq_file *m
 EXPORT_SYMBOL_GPL(drm_gem_cma_describe);
 #endif
 
-/* low-level interface prime helpers */
+/**
+ * drm_gem_cma_prime_get_sg_table - provide a scatter/gather table of pinned
+ *     pages for a CMA GEM object
+ * @obj: GEM object
+ *
+ * This function exports a scatter/gather table suitable for PRIME usage by
+ * calling the standard DMA mapping API. Drivers using the CMA helpers should
+ * set this as their DRM driver's ->gem_prime_get_sg_table() callback.
+ *
+ * Returns:
+ * A pointer to the scatter/gather table of pinned pages or NULL on failure.
+ */
 struct sg_table *drm_gem_cma_prime_get_sg_table(struct drm_gem_object *obj)
 {
 	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
@@ -315,6 +432,23 @@ out:
 }
 EXPORT_SYMBOL_GPL(drm_gem_cma_prime_get_sg_table);
 
+/**
+ * drm_gem_cma_prime_import_sg_table - produce a CMA GEM object from another
+ *     driver's scatter/gather table of pinned pages
+ * @dev: device to import into
+ * @attach: DMA-BUF attachment
+ * @sgt: scatter/gather table of pinned pages
+ *
+ * This function imports a scatter/gather table exported via DMA-BUF by
+ * another driver. Imported buffers must be physically contiguous in memory
+ * (i.e. the scatter/gather table must contain a single entry). Drivers that
+ * use the CMA helpers should set this as their DRM driver's
+ * ->gem_prime_import_sg_table() callback.
+ *
+ * Returns:
+ * A pointer to a newly created GEM object or an ERR_PTR-encoded negative
+ * error code on failure.
+ */
 struct drm_gem_object *
 drm_gem_cma_prime_import_sg_table(struct drm_device *dev,
 				  struct dma_buf_attachment *attach,
@@ -339,6 +473,18 @@ drm_gem_cma_prime_import_sg_table(struct drm_device *dev,
 }
 EXPORT_SYMBOL_GPL(drm_gem_cma_prime_import_sg_table);
 
+/**
+ * drm_gem_cma_prime_mmap - memory-map an exported CMA GEM object
+ * @obj: GEM object
+ * @vma: VMA for the area to be mapped
+ *
+ * This function maps a buffer imported via DRM PRIME into a userspace
+ * process's address space. Drivers that use the CMA helpers should set this
+ * as their DRM driver's ->gem_prime_mmap() callback.
+ *
+ * Returns:
+ * 0 on success or a negative error code on failure.
+ */
 int drm_gem_cma_prime_mmap(struct drm_gem_object *obj,
 			   struct vm_area_struct *vma)
 {
@@ -357,6 +503,20 @@ int drm_gem_cma_prime_mmap(struct drm_gem_object *obj,
 }
 EXPORT_SYMBOL_GPL(drm_gem_cma_prime_mmap);
 
+/**
+ * drm_gem_cma_prime_vmap - map a CMA GEM object into the kernel's virtual
+ *     address space
+ * @obj: GEM object
+ *
+ * This function maps a buffer exported via DRM PRIME into the kernel's
+ * virtual address space. Since the CMA buffers are already mapped into the
+ * kernel virtual address space this simply returns the cached virtual
+ * address. Drivers using the CMA helpers should set this as their DRM
+ * driver's ->gem_prime_vmap() callback.
+ *
+ * Returns:
+ * The kernel virtual address of the CMA GEM object's backing store.
+ */
 void *drm_gem_cma_prime_vmap(struct drm_gem_object *obj)
 {
 	struct drm_gem_cma_object *cma_obj = to_drm_gem_cma_obj(obj);
@@ -365,6 +525,17 @@ void *drm_gem_cma_prime_vmap(struct drm_gem_object *obj)
 }
 EXPORT_SYMBOL_GPL(drm_gem_cma_prime_vmap);
 
+/**
+ * drm_gem_cma_prime_vunmap - unmap a CMA GEM object from the kernel's virtual
+ *     address space
+ * @obj: GEM object
+ * @vaddr: kernel virtual address where the CMA GEM object was mapped
+ *
+ * This function removes a buffer exported via DRM PRIME from the kernel's
+ * virtual address space. This is a no-op because CMA buffers cannot be
+ * unmapped from kernel space. Drivers using the CMA helpers should set this
+ * as their DRM driver's ->gem_prime_vunmap() callback.
+ */
 void drm_gem_cma_prime_vunmap(struct drm_gem_object *obj, void *vaddr)
 {
 	/* Nothing to do */
diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
index e4849413ee80..aeb91ed653c9 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem.c
@@ -612,8 +612,7 @@ int omap_gem_dumb_create(struct drm_file *file, struct drm_device *dev,
 {
 	union omap_gem_size gsize;
 
-	/* in case someone tries to feed us a completely bogus stride: */
-	args->pitch = align_pitch(args->pitch, args->width, args->bpp);
+	args->pitch = align_pitch(0, args->width, args->bpp);
 	args->size = PAGE_ALIGN(args->pitch * args->height);
 
 	gsize = (union omap_gem_size){
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_kms.c b/drivers/gpu/drm/rcar-du/rcar_du_kms.c
index 6c24ad7d03ef..6289e3797bc5 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_kms.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_kms.c
@@ -126,9 +126,9 @@ int rcar_du_dumb_create(struct drm_file *file, struct drm_device *dev,
 	else
 		align = 16 * args->bpp / 8;
 
-	args->pitch = roundup(max(args->pitch, min_pitch), align);
+	args->pitch = roundup(min_pitch, align);
 
-	return drm_gem_cma_dumb_create(file, dev, args);
+	return drm_gem_cma_dumb_create_internal(file, dev, args);
 }
 
 static struct drm_framebuffer *
diff --git a/include/drm/drm_gem_cma_helper.h b/include/drm/drm_gem_cma_helper.h
index 2ff35f3de9c5..acd6af8a8e67 100644
--- a/include/drm/drm_gem_cma_helper.h
+++ b/include/drm/drm_gem_cma_helper.h
@@ -4,6 +4,13 @@
 #include <drm/drmP.h>
 #include <drm/drm_gem.h>
 
+/**
+ * struct drm_gem_cma_object - GEM object backed by CMA memory allocations
+ * @base: base GEM object
+ * @paddr: physical address of the backing memory
+ * @sgt: scatter/gather table for imported PRIME buffers
+ * @vaddr: kernel virtual address of the backing memory
+ */
 struct drm_gem_cma_object {
 	struct drm_gem_object base;
 	dma_addr_t paddr;
@@ -19,23 +26,30 @@ to_drm_gem_cma_obj(struct drm_gem_object *gem_obj)
 	return container_of(gem_obj, struct drm_gem_cma_object, base);
 }
 
-/* free gem object. */
+/* free GEM object */
 void drm_gem_cma_free_object(struct drm_gem_object *gem_obj);
 
-/* create memory region for drm framebuffer. */
+/* create memory region for DRM framebuffer */
+int drm_gem_cma_dumb_create_internal(struct drm_file *file_priv,
+				     struct drm_device *drm,
+				     struct drm_mode_create_dumb *args);
+
+/* create memory region for DRM framebuffer */
 int drm_gem_cma_dumb_create(struct drm_file *file_priv,
-		struct drm_device *drm, struct drm_mode_create_dumb *args);
+			    struct drm_device *drm,
+			    struct drm_mode_create_dumb *args);
 
-/* map memory region for drm framebuffer to user space. */
+/* map memory region for DRM framebuffer to user space */
 int drm_gem_cma_dumb_map_offset(struct drm_file *file_priv,
-		struct drm_device *drm, uint32_t handle, uint64_t *offset);
+				struct drm_device *drm, u32 handle,
+				u64 *offset);
 
-/* set vm_flags and we can change the vm attribute to other one at here. */
+/* set vm_flags and we can change the VM attribute to other one at here */
 int drm_gem_cma_mmap(struct file *filp, struct vm_area_struct *vma);
 
-/* allocate physical memory. */
+/* allocate physical memory */
 struct drm_gem_cma_object *drm_gem_cma_create(struct drm_device *drm,
-		unsigned int size);
+					      size_t size);
 
 extern const struct vm_operations_struct drm_gem_cma_vm_ops;