[PATCH v2 7/7] drm: Document how to register devices without struct drm_bus

Thierry Reding thierry.reding at gmail.com
Tue May 13 08:30:50 PDT 2014

From: Thierry Reding <treding at nvidia.com>

With the recent addition of the drm_set_unique() function, devices can
now be registered without requiring a drm_bus. Add a brief description
to the DRM docbook to show how that can be achieved.

Signed-off-by: Thierry Reding <treding at nvidia.com>
 Documentation/DocBook/drm.tmpl | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
index f26a8e4fbe47..f48227caf41a 100644
--- a/Documentation/DocBook/drm.tmpl
+++ b/Documentation/DocBook/drm.tmpl
@@ -142,6 +142,12 @@
       to register it with the DRM subsystem.
+      Newer drivers that no longer require a <structname>drm_bus</structname>
+      structure can alternatively use the low-level device initialization and
+      registration functions such as <function>drm_dev_alloc()</function> and
+      <function>drm_dev_register()</function> directly.
+    </para>
+    <para>
       The <structname>drm_driver</structname> structure contains static
       information that describes the driver and features it supports, and
       pointers to methods that the DRM core will call to implement the DRM API.
@@ -290,6 +296,29 @@ char *date;</synopsis>
 !Fdrivers/gpu/drm/drm_pci.c drm_pci_init drm_pci_exit
 !Fdrivers/gpu/drm/drm_usb.c drm_usb_init drm_usb_exit
 !Fdrivers/gpu/drm/drm_platform.c drm_platform_init
+      <para>
+        New drivers that no longer rely on the services provided by the
+        <structname>drm_bus</structname> structure can call the low-level
+        device registration functions directly. The
+        <function>drm_dev_alloc()</function> function can be used to allocate
+        and initialize a new <structname>drm_device</structname> structure.
+        Drivers will typically want to perform some additional setup on this
+        structure, such as allocating driver-specific data and storing a
+        pointer to it in the DRM device's <structfield>dev_private</structfield>
+        field. Drivers should also set the device's unique name using the
+        <function>drm_set_unique()</function> function. After it has been set up
+        a device can be registered with the DRM subsystem by calling
+        <function>drm_dev_register()</function>. This will cause the device to
+        be exposed to userspace and will call the driver's
+        <structfield>.load()</structfield> implementation. When a device is
+        removed, the DRM device can safely be unregistered and freed using a
+        call to <function>drm_put_dev()</function>.
+      </para>
+!Fdrivers/gpu/drm/drm_stub.c drm_dev_alloc
+!Fdrivers/gpu/drm/drm_stub.c drm_set_unique
+!Fdrivers/gpu/drm/drm_stub.c drm_dev_register
+!Fdrivers/gpu/drm/drm_stub.c drm_put_dev
+    </sect2>
       <title>Driver Load</title>

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