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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="drmDevelopersGuide">
+  <bookinfo>
+    <title>Linux DRM Developer's Guide</title>
+
+    <copyright>
+      <year>2008-2009</year>
+      <holder>
+	Intel Corporation (Jesse Barnes &lt;jesse.barnes@intel.com&gt;)
+      </holder>
+    </copyright>
+
+    <legalnotice>
+      <para>
+	The contents of this file may be used under the terms of the GNU
+	General Public License version 2 (the "GPL") as distributed in
+	the kernel source COPYING file.
+      </para>
+    </legalnotice>
+  </bookinfo>
+
+<toc></toc>
+
+  <!-- Introduction -->
+
+  <chapter id="drmIntroduction">
+    <title>Introduction</title>
+    <para>
+      The Linux DRM layer contains code intended to support the needs
+      of complex graphics devices, usually containing programmable
+      pipelines well suited to 3D graphics acceleration.  Graphics
+      drivers in the kernel may make use of DRM functions to make
+      tasks like memory management, interrupt handling and DMA easier,
+      and provide a uniform interface to applications.
+    </para>
+    <para>
+      A note on versions: this guide covers features found in the DRM
+      tree, including the TTM memory manager, output configuration and
+      mode setting, and the new vblank internals, in addition to all
+      the regular features found in current kernels.
+    </para>
+    <para>
+      [Insert diagram of typical DRM stack here]
+    </para>
+  </chapter>
+
+  <!-- Internals -->
+
+  <chapter id="drmInternals">
+    <title>DRM Internals</title>
+    <para>
+      This chapter documents DRM internals relevant to driver authors
+      and developers working to add support for the latest features to
+      existing drivers.
+    </para>
+    <para>
+      First, we go over some typical driver initialization
+      requirements, like setting up command buffers, creating an
+      initial output configuration, and initializing core services.
+      Subsequent sections cover core internals in more detail,
+      providing implementation notes and examples.
+    </para>
+    <para>
+      The DRM layer provides several services to graphics drivers,
+      many of them driven by the application interfaces it provides
+      through libdrm, the library that wraps most of the DRM ioctls.
+      These include vblank event handling, memory
+      management, output management, framebuffer management, command
+      submission &amp; fencing, suspend/resume support, and DMA
+      services.
+    </para>
+    <para>
+      The core of every DRM driver is struct drm_driver.  Drivers
+      typically statically initialize a drm_driver structure,
+      then pass it to drm_init() at load time.
+    </para>
+
+  <!-- Internals: driver init -->
+
+  <sect1>
+    <title>Driver initialization</title>
+    <para>
+      Before calling the DRM initialization routines, the driver must
+      first create and fill out a struct drm_driver structure.
+    </para>
+    <programlisting>
+      static struct drm_driver driver = {
+	/* Don't use MTRRs here; the Xserver or userspace app should
+	 * deal with them for Intel hardware.
+	 */
+	.driver_features =
+	    DRIVER_USE_AGP | DRIVER_REQUIRE_AGP |
+	    DRIVER_HAVE_IRQ | DRIVER_IRQ_SHARED | DRIVER_MODESET,
+	.load = i915_driver_load,
+	.unload = i915_driver_unload,
+	.firstopen = i915_driver_firstopen,
+	.lastclose = i915_driver_lastclose,
+	.preclose = i915_driver_preclose,
+	.save = i915_save,
+	.restore = i915_restore,
+	.device_is_agp = i915_driver_device_is_agp,
+	.get_vblank_counter = i915_get_vblank_counter,
+	.enable_vblank = i915_enable_vblank,
+	.disable_vblank = i915_disable_vblank,
+	.irq_preinstall = i915_driver_irq_preinstall,
+	.irq_postinstall = i915_driver_irq_postinstall,
+	.irq_uninstall = i915_driver_irq_uninstall,
+	.irq_handler = i915_driver_irq_handler,
+	.reclaim_buffers = drm_core_reclaim_buffers,
+	.get_map_ofs = drm_core_get_map_ofs,
+	.get_reg_ofs = drm_core_get_reg_ofs,
+	.fb_probe = intelfb_probe,
+	.fb_remove = intelfb_remove,
+	.fb_resize = intelfb_resize,
+	.master_create = i915_master_create,
+	.master_destroy = i915_master_destroy,
+#if defined(CONFIG_DEBUG_FS)
+	.debugfs_init = i915_debugfs_init,
+	.debugfs_cleanup = i915_debugfs_cleanup,
+#endif
+	.gem_init_object = i915_gem_init_object,
+	.gem_free_object = i915_gem_free_object,
+	.gem_vm_ops = &amp;i915_gem_vm_ops,
+	.ioctls = i915_ioctls,
+	.fops = {
+		.owner = THIS_MODULE,
+		.open = drm_open,
+		.release = drm_release,
+		.ioctl = drm_ioctl,
+		.mmap = drm_mmap,
+		.poll = drm_poll,
+		.fasync = drm_fasync,
+#ifdef CONFIG_COMPAT
+		.compat_ioctl = i915_compat_ioctl,
+#endif
+		.llseek = noop_llseek,
+		},
+	.pci_driver = {
+		.name = DRIVER_NAME,
+		.id_table = pciidlist,
+		.probe = probe,
+		.remove = __devexit_p(drm_cleanup_pci),
+		},
+	.name = DRIVER_NAME,
+	.desc = DRIVER_DESC,
+	.date = DRIVER_DATE,
+	.major = DRIVER_MAJOR,
+	.minor = DRIVER_MINOR,
+	.patchlevel = DRIVER_PATCHLEVEL,
+      };
+    </programlisting>
+    <para>
+      In the example above, taken from the i915 DRM driver, the driver
+      sets several flags indicating what core features it supports;
+      we go over the individual callbacks in later sections.  Since
+      flags indicate which features your driver supports to the DRM
+      core, you need to set most of them prior to calling drm_init().  Some,
+      like DRIVER_MODESET can be set later based on user supplied parameters,
+      but that's the exception rather than the rule.
+    </para>
+    <variablelist>
+      <title>Driver flags</title>
+      <varlistentry>
+	<term>DRIVER_USE_AGP</term>
+	<listitem><para>
+	    Driver uses AGP interface
+	</para></listitem>
+      </varlistentry>
+      <varlistentry>
+	<term>DRIVER_REQUIRE_AGP</term>
+	<listitem><para>
+	    Driver needs AGP interface to function.
+	</para></listitem>
+      </varlistentry>
+      <varlistentry>
+	<term>DRIVER_USE_MTRR</term>
+	<listitem>
+	  <para>
+	    Driver uses MTRR interface for mapping memory.  Deprecated.
+	  </para>
+	</listitem>
+      </varlistentry>
+      <varlistentry>
+	<term>DRIVER_PCI_DMA</term>
+	<listitem><para>
+	    Driver is capable of PCI DMA.  Deprecated.
+	</para></listitem>
+      </varlistentry>
+      <varlistentry>
+	<term>DRIVER_SG</term>
+	<listitem><para>
+	    Driver can perform scatter/gather DMA.  Deprecated.
+	</para></listitem>
+      </varlistentry>
+      <varlistentry>
+	<term>DRIVER_HAVE_DMA</term>
+	<listitem><para>Driver supports DMA.  Deprecated.</para></listitem>
+      </varlistentry>
+      <varlistentry>
+	<term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
+	<listitem>
+	  <para>
+	    DRIVER_HAVE_IRQ indicates whether the driver has an IRQ
+	    handler.  DRIVER_IRQ_SHARED indicates whether the device &amp;
+	    handler support shared IRQs (note that this is required of
+	    PCI drivers).
+	  </para>
+	</listitem>
+      </varlistentry>
+      <varlistentry>
+	<term>DRIVER_DMA_QUEUE</term>
+	<listitem>
+	  <para>
+	    Should be set if the driver queues DMA requests and completes them
+	    asynchronously.  Deprecated.
+	  </para>
+	</listitem>
+      </varlistentry>
+      <varlistentry>
+	<term>DRIVER_FB_DMA</term>
+	<listitem>
+	  <para>
+	    Driver supports DMA to/from the framebuffer.  Deprecated.
+	  </para>
+	</listitem>
+      </varlistentry>
+      <varlistentry>
+	<term>DRIVER_MODESET</term>
+	<listitem>
+	  <para>
+	    Driver supports mode setting interfaces.
+	  </para>
+	</listitem>
+      </varlistentry>
+    </variablelist>
+    <para>
+      In this specific case, the driver requires AGP and supports
+      IRQs.  DMA, as discussed later, is handled by device-specific ioctls
+      in this case.  It also supports the kernel mode setting APIs, though
+      unlike in the actual i915 driver source, this example unconditionally
+      exports KMS capability.
+    </para>
+  </sect1>
+
+  <!-- Internals: driver load -->
+
+  <sect1>
+    <title>Driver load</title>
+    <para>
+      In the previous section, we saw what a typical drm_driver
+      structure might look like.  One of the more important fields in
+      the structure is the hook for the load function.
+    </para>
+    <programlisting>
+      static struct drm_driver driver = {
+      	...
+      	.load = i915_driver_load,
+        ...
+      };
+    </programlisting>
+    <para>
+      The load function has many responsibilities: allocating a driver
+      private structure, specifying supported performance counters,
+      configuring the device (e.g. mapping registers &amp; command
+      buffers), initializing the memory manager, and setting up the
+      initial output configuration.
+    </para>
+    <para>
+      If compatibility is a concern (e.g. with drivers converted over
+      to the new interfaces from the old ones), care must be taken to
+      prevent device initialization and control that is incompatible with
+      currently active userspace drivers.  For instance, if user
+      level mode setting drivers are in use, it would be problematic
+      to perform output discovery &amp; configuration at load time.
+      Likewise, if user-level drivers unaware of memory management are
+      in use, memory management and command buffer setup may need to
+      be omitted.  These requirements are driver-specific, and care
+      needs to be taken to keep both old and new applications and
+      libraries working.  The i915 driver supports the "modeset"
+      module parameter to control whether advanced features are
+      enabled at load time or in legacy fashion.
+    </para>
+
+    <sect2>
+      <title>Driver private &amp; performance counters</title>
+      <para>
+	The driver private hangs off the main drm_device structure and
+	can be used for tracking various device-specific bits of
+	information, like register offsets, command buffer status,
+	register state for suspend/resume, etc.  At load time, a
+	driver may simply allocate one and set drm_device.dev_priv
+	appropriately; it should be freed and drm_device.dev_priv set
+	to NULL when the driver is unloaded.
+      </para>
+      <para>
+	The DRM supports several counters which may be used for rough
+	performance characterization.  Note that the DRM stat counter
+	system is not often used by applications, and supporting
+	additional counters is completely optional.
+      </para>
+      <para>
+	These interfaces are deprecated and should not be used.  If performance
+	monitoring is desired, the developer should investigate and
+	potentially enhance the kernel perf and tracing infrastructure to export
+	GPU related performance information for consumption by performance
+	monitoring tools and applications.
+      </para>
+    </sect2>
+
+    <sect2>
+      <title>Configuring the device</title>
+      <para>
+	Obviously, device configuration is device-specific.
+	However, there are several common operations: finding a
+	device's PCI resources, mapping them, and potentially setting
+	up an IRQ handler.
+      </para>
+      <para>
+	Finding &amp; mapping resources is fairly straightforward.  The
+	DRM wrapper functions, drm_get_resource_start() and
+	drm_get_resource_len(), may be used to find BARs on the given
+	drm_device struct.  Once those values have been retrieved, the
+	driver load function can call drm_addmap() to create a new
+	mapping for the BAR in question.  Note that you probably want a
+	drm_local_map_t in your driver private structure to track any
+	mappings you create.
+<!-- !Fdrivers/gpu/drm/drm_bufs.c drm_get_resource_* -->
+<!-- !Finclude/drm/drmP.h drm_local_map_t -->
+      </para>
+      <para>
+	if compatibility with other operating systems isn't a concern
+	(DRM drivers can run under various BSD variants and OpenSolaris),
+	native Linux calls may be used for the above, e.g. pci_resource_*
+	and iomap*/iounmap.  See the Linux device driver book for more
+	info.
+      </para>
+      <para>
+	Once you have a register map, you may use the DRM_READn() and
+	DRM_WRITEn() macros to access the registers on your device, or
+	use driver-specific versions to offset into your MMIO space
+	relative to a driver-specific base pointer (see I915_READ for
+	an example).
+      </para>
+      <para>
+	If your device supports interrupt generation, you may want to
+	set up an interrupt handler when the driver is loaded.  This
+	is done using the drm_irq_install() function.  If your device
+	supports vertical blank interrupts, it should call
+	drm_vblank_init() to initialize the core vblank handling code before
+	enabling interrupts on your device.  This ensures the vblank related
+	structures are allocated and allows the core to handle vblank events.
+      </para>
+<!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
+      <para>
+	Once your interrupt handler is registered (it uses your
+	drm_driver.irq_handler as the actual interrupt handling
+	function), you can safely enable interrupts on your device,
+	assuming any other state your interrupt handler uses is also
+	initialized.
+      </para>
+      <para>
+	Another task that may be necessary during configuration is
+	mapping the video BIOS.  On many devices, the VBIOS describes
+	device configuration, LCD panel timings (if any), and contains
+	flags indicating device state.  Mapping the BIOS can be done
+	using the pci_map_rom() call, a convenience function that
+	takes care of mapping the actual ROM, whether it has been
+	shadowed into memory (typically at address 0xc0000) or exists
+	on the PCI device in the ROM BAR.  Note that after the ROM
+	has been mapped and any necessary information has been extracted,
+	it should be unmapped; on many devices, the ROM address decoder is
+	shared with other BARs, so leaving it mapped could cause
+	undesired behavior like hangs or memory corruption.
+<!--!Fdrivers/pci/rom.c pci_map_rom-->
+      </para>
+    </sect2>
+
+    <sect2>
+      <title>Memory manager initialization</title>
+      <para>
+	In order to allocate command buffers, cursor memory, scanout
+	buffers, etc., as well as support the latest features provided
+	by packages like Mesa and the X.Org X server, your driver
+	should support a memory manager.
+      </para>
+      <para>
+	If your driver supports memory management (it should!), you
+	need to set that up at load time as well.  How you initialize
+	it depends on which memory manager you're using: TTM or GEM.
+      </para>
+      <sect3>
+	<title>TTM initialization</title>
+	<para>
+	  TTM (for Translation Table Manager) manages video memory and
+	  aperture space for graphics devices. TTM supports both UMA devices
+	  and devices with dedicated video RAM (VRAM), i.e. most discrete
+	  graphics devices.  If your device has dedicated RAM, supporting
+	  TTM is desirable.  TTM also integrates tightly with your
+	  driver-specific buffer execution function.  See the radeon
+	  driver for examples.
+	</para>
+	<para>
+	  The core TTM structure is the ttm_bo_driver struct.  It contains
+	  several fields with function 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>
+      </sect3>
+      <sect3>
+	<title>GEM initialization</title>
+	<para>
+	  GEM is an alternative to TTM, designed specifically for UMA
+	  devices.  It has simpler initialization and execution requirements
+	  than TTM, but has no VRAM management capability.  Core GEM
+	  is initialized by calling drm_mm_init() to create
+	  a GTT DRM MM object, which provides an address space pool for
+	  object allocation.  In a KMS configuration, the driver
+	  needs to allocate and initialize a command ring buffer following
+	  core GEM initialization.  A UMA device usually has what is called a
+	  "stolen" memory region, which provides space for the initial
+	  framebuffer and large, contiguous memory regions required by the
+	  device.  This space is not typically managed by GEM, and it must
+	  be initialized separately into its own DRM MM object.
+	</para>
+	<para>
+	  Initialization is driver-specific. In the case of Intel
+	  integrated graphics chips like 965GM, GEM initialization can
+	  be done by calling the internal GEM init function,
+	  i915_gem_do_init().  Since the 965GM is a UMA device
+	  (i.e. it doesn't have dedicated VRAM), GEM manages
+	  making regular RAM available for GPU operations.  Memory set
+	  aside by the BIOS (called "stolen" memory by the i915
+	  driver) is managed by the DRM memrange allocator; the
+	  rest of the aperture is managed by GEM.
+	  <programlisting>
+	    /* Basic memrange allocator for stolen space (aka vram) */
+	    drm_memrange_init(&amp;dev_priv->vram, 0, prealloc_size);
+	    /* Let GEM Manage from end of prealloc space to end of aperture */
+	    i915_gem_do_init(dev, prealloc_size, agp_size);
+	  </programlisting>
+<!--!Edrivers/char/drm/drm_memrange.c-->
+	</para>
+	<para>
+	  Once the memory manager has been set up, we may allocate the
+	  command buffer.  In the i915 case, this is also done with a
+	  GEM function, i915_gem_init_ringbuffer().
+	</para>
+      </sect3>
+    </sect2>
+
+    <sect2>
+      <title>Output configuration</title>
+      <para>
+	The final initialization task is output configuration.  This involves:
+	<itemizedlist>
+	  <listitem>
+	    Finding and initializing the CRTCs, encoders, and connectors
+	    for the device.
+	  </listitem>
+	  <listitem>
+	    Creating an initial configuration.
+	  </listitem>
+	  <listitem>
+	    Registering a framebuffer console driver.
+	  </listitem>
+	</itemizedlist>
+      </para>
+      <sect3>
+	<title>Output discovery and initialization</title>
+	<para>
+	  Several core functions exist to create CRTCs, encoders, and
+	  connectors, namely: drm_crtc_init(), drm_connector_init(), and
+	  drm_encoder_init(), along with several "helper" functions to
+	  perform common tasks.
+	</para>
+	<para>
+	  Connectors should be registered with sysfs once they've been
+	  detected and initialized, using the
+	  drm_sysfs_connector_add() function.  Likewise, when they're
+	  removed from the system, they should be destroyed with
+	  drm_sysfs_connector_remove().
+	</para>
+	<programlisting>
+<![CDATA[
+void intel_crt_init(struct drm_device *dev)
+{
+	struct drm_connector *connector;
+	struct intel_output *intel_output;
+
+	intel_output = kzalloc(sizeof(struct intel_output), GFP_KERNEL);
+	if (!intel_output)
+		return;
+
+	connector = &intel_output->base;
+	drm_connector_init(dev, &intel_output->base,
+			   &intel_crt_connector_funcs, DRM_MODE_CONNECTOR_VGA);
+
+	drm_encoder_init(dev, &intel_output->enc, &intel_crt_enc_funcs,
+			 DRM_MODE_ENCODER_DAC);
+
+	drm_mode_connector_attach_encoder(&intel_output->base,
+					  &intel_output->enc);
+
+	/* Set up the DDC bus. */
+	intel_output->ddc_bus = intel_i2c_create(dev, GPIOA, "CRTDDC_A");
+	if (!intel_output->ddc_bus) {
+		dev_printk(KERN_ERR, &dev->pdev->dev, "DDC bus registration "
+			   "failed.\n");
+		return;
+	}
+
+	intel_output->type = INTEL_OUTPUT_ANALOG;
+	connector->interlace_allowed = 0;
+	connector->doublescan_allowed = 0;
+
+	drm_encoder_helper_add(&intel_output->enc, &intel_crt_helper_funcs);
+	drm_connector_helper_add(connector, &intel_crt_connector_helper_funcs);
+
+	drm_sysfs_connector_add(connector);
+}
+]]>
+	</programlisting>
+	<para>
+	  In the example above (again, taken from the i915 driver), a
+	  CRT connector and encoder combination is created.  A device-specific
+	  i2c bus is also created for fetching EDID data and
+	  performing monitor detection.  Once the process is complete,
+	  the new connector is registered with sysfs to make its
+	  properties available to applications.
+	</para>
+	<sect4>
+	  <title>Helper functions and core functions</title>
+	  <para>
+	    Since many PC-class graphics devices have similar display output
+	    designs, the DRM provides a set of helper functions to make
+	    output management easier.  The core helper routines handle
+	    encoder re-routing and the disabling of unused functions following
+	    mode setting.  Using the helpers is optional, but recommended for
+	    devices with PC-style architectures (i.e. a set of display planes
+	    for feeding pixels to encoders which are in turn routed to
+	    connectors).  Devices with more complex requirements needing
+	    finer grained management may opt to use the core callbacks
+	    directly.
+	  </para>
+	  <para>
+	    [Insert typical diagram here.]  [Insert OMAP style config here.]
+	  </para>
+	</sect4>
+	<para>
+	  Each encoder object needs to provide:
+	  <itemizedlist>
+	    <listitem>
+	      A DPMS (basically on/off) function.
+	    </listitem>
+	    <listitem>
+	      A mode-fixup function (for converting requested modes into
+	      native hardware timings).
+	    </listitem>
+	    <listitem>
+	      Functions (prepare, set, and commit) for use by the core DRM
+	      helper functions.
+	    </listitem>
+	  </itemizedlist>
+	  Connector helpers need to provide functions (mode-fetch, validity,
+	  and encoder-matching) for returning an ideal encoder for a given
+	  connector.  The core connector functions include a DPMS callback,
+	  save/restore routines (deprecated), detection, mode probing,
+	  property handling, and cleanup functions.
+	</para>
+<!--!Edrivers/char/drm/drm_crtc.h-->
+<!--!Edrivers/char/drm/drm_crtc.c-->
+<!--!Edrivers/char/drm/drm_crtc_helper.c-->
+      </sect3>
+    </sect2>
+  </sect1>
+
+  <!-- Internals: vblank handling -->
+
+  <sect1>
+    <title>VBlank event handling</title>
+    <para>
+      The DRM core exposes two vertical blank related ioctls:
+      <variablelist>
+        <varlistentry>
+          <term>DRM_IOCTL_WAIT_VBLANK</term>
+          <listitem>
+            <para>
+              This takes a struct drm_wait_vblank structure as its argument,
+              and it is used to block or request a signal when a specified
+              vblank event occurs.
+            </para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term>DRM_IOCTL_MODESET_CTL</term>
+          <listitem>
+            <para>
+              This should be called by application level drivers before and
+              after mode setting, since on many devices the vertical blank
+              counter is reset at that time.  Internally, the DRM snapshots
+              the last vblank count when the ioctl is called with the
+              _DRM_PRE_MODESET command, so that the counter won't go backwards
+              (which is dealt with when _DRM_POST_MODESET is used).
+            </para>
+          </listitem>
+        </varlistentry>
+      </variablelist>
+<!--!Edrivers/char/drm/drm_irq.c-->
+    </para>
+    <para>
+      To support the functions above, the DRM core provides several
+      helper functions for tracking vertical blank counters, and
+      requires drivers to provide several callbacks:
+      get_vblank_counter(), enable_vblank() and disable_vblank().  The
+      core uses get_vblank_counter() to keep the counter accurate
+      across interrupt disable periods.  It should return the current
+      vertical blank event count, which is often tracked in a device
+      register.  The enable and disable vblank callbacks should enable
+      and disable vertical blank interrupts, respectively.  In the
+      absence of DRM clients waiting on vblank events, the core DRM
+      code uses the disable_vblank() function to disable
+      interrupts, which saves power.  They are re-enabled again when
+      a client calls the vblank wait ioctl above.
+    </para>
+    <para>
+      A device that doesn't provide a count register may simply use an
+      internal atomic counter incremented on every vertical blank
+      interrupt (and then treat the enable_vblank() and disable_vblank()
+      callbacks as no-ops).
+    </para>
+  </sect1>
+
+  <sect1>
+    <title>Memory management</title>
+    <para>
+      The memory manager lies at the heart of many DRM operations; it
+      is required to support advanced client features like OpenGL
+      pbuffers.  The DRM currently contains two memory managers: TTM
+      and GEM.
+    </para>
+
+    <sect2>
+      <title>The Translation Table Manager (TTM)</title>
+      <para>
+	TTM was developed by Tungsten Graphics, primarily by Thomas
+	Hellström, and is intended to be a flexible, high performance
+	graphics memory manager.
+      </para>
+      <para>
+	Drivers wishing to support TTM must fill out a drm_bo_driver
+	structure.
+      </para>
+      <para>
+	TTM design background and information belongs here.
+      </para>
+    </sect2>
+
+    <sect2>
+      <title>The Graphics Execution Manager (GEM)</title>
+      <para>
+	GEM is an Intel project, authored by Eric Anholt and Keith
+	Packard.  It provides simpler interfaces than TTM, and is well
+	suited for UMA devices.
+      </para>
+      <para>
+	GEM-enabled drivers must provide gem_init_object() and
+	gem_free_object() callbacks to support the core memory
+	allocation routines.  They should also provide several driver-specific
+	ioctls to support command execution, pinning, buffer
+	read &amp; write, mapping, and domain ownership transfers.
+      </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 provided by Linux's shmem layer, which
+	provides memory to back each object.  When mapped into the GTT
+	or used in a command buffer, the backing pages for an object are
+	flushed to memory and marked write combined so as to be coherent
+	with the GPU.  Likewise, if the CPU accesses an object after the GPU
+	has finished rendering to the object, then the object must be made
+	coherent with the CPU's view
+	of memory, usually involving GPU cache flushing of various kinds.
+	This core CPU&lt;-&gt;GPU coherency management is provided by a
+	device-specific ioctl, which evaluates an object's current domain and
+	performs any necessary flushing or synchronization to put the object
+	into the desired coherency domain (note that the object may be busy,
+	i.e. an active render target; in that case, setting the domain
+	blocks the client and waits for rendering to complete before
+	performing any necessary flushing operations).
+      </para>
+      <para>
+	Perhaps the most important GEM function 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 bind
+	all the objects into the GTT, execute the buffer, and provide
+	necessary synchronization between clients accessing the same buffers.
+	This often involves evicting some objects from the GTT and re-binding
+	others (a fairly expensive operation), and providing relocation
+	support which hides fixed GTT offsets from clients.  Clients must
+	take care not to submit command buffers that reference more objects
+	than can fit in the GTT; otherwise, GEM will reject them and no rendering
+	will occur.  Similarly, if several objects in the buffer require
+	fence registers to be allocated for correct rendering (e.g. 2D blits
+	on pre-965 chips), care must be taken not to require more fence
+	registers than are available to the client.  Such resource management
+	should be abstracted from the client in libdrm.
+      </para>
+    </sect2>
+
+  </sect1>
+
+  <!-- Output management -->
+  <sect1>
+    <title>Output management</title>
+    <para>
+      At the core of the DRM output management code is a set of
+      structures representing CRTCs, encoders, and connectors.
+    </para>
+    <para>
+      A CRTC is an abstraction representing a part of the chip that
+      contains a pointer to a scanout buffer.  Therefore, the number
+      of CRTCs available determines how many independent scanout
+      buffers can be active at any given time.  The CRTC structure
+      contains several fields to support this: a pointer to some video
+      memory, a display mode, and an (x, y) offset into the video
+      memory to support panning or configurations where one piece of
+      video memory spans multiple CRTCs.
+    </para>
+    <para>
+      An encoder takes pixel data from a CRTC and converts it to a
+      format suitable for any attached connectors.  On some devices,
+      it may be possible to have a CRTC send data to more than one
+      encoder.  In that case, both encoders would receive data from
+      the same scanout buffer, resulting in a "cloned" display
+      configuration across the connectors attached to each encoder.
+    </para>
+    <para>
+      A connector is the final destination for pixel data on a device,
+      and usually connects directly to an external display device like
+      a monitor or laptop panel.  A connector can only be attached to
+      one encoder at a time.  The connector is also the structure
+      where information about the attached display is kept, so it
+      contains fields for display data, EDID data, DPMS &amp;
+      connection status, and information about modes supported on the
+      attached displays.
+    </para>
+<!--!Edrivers/char/drm/drm_crtc.c-->
+  </sect1>
+
+  <sect1>
+    <title>Framebuffer management</title>
+    <para>
+      Clients need to provide a framebuffer object which provides a source
+      of pixels for a CRTC to deliver to the encoder(s) and ultimately the
+      connector(s). A framebuffer is fundamentally a driver-specific memory
+      object, made into an opaque handle by the DRM's addfb() function.
+      Once a framebuffer has been created this way, it may be passed to the
+      KMS mode setting routines for use in a completed configuration.
+    </para>
+  </sect1>
+
+  <sect1>
+    <title>Command submission &amp; fencing</title>
+    <para>
+      This should cover a few device-specific command submission
+      implementations.
+    </para>
+  </sect1>
+
+  <sect1>
+    <title>Suspend/resume</title>
+    <para>
+      The DRM core provides some suspend/resume code, but drivers
+      wanting full suspend/resume support should provide save() and
+      restore() functions.  These are called at suspend,
+      hibernate, or resume time, and should perform any state save or
+      restore required by your device across suspend or hibernate
+      states.
+    </para>
+  </sect1>
+
+  <sect1>
+    <title>DMA services</title>
+    <para>
+      This should cover how DMA mapping etc. is supported by the core.
+      These functions are deprecated and should not be used.
+    </para>
+  </sect1>
+  </chapter>
+
+  <!-- External interfaces -->
+
+  <chapter id="drmExternals">
+    <title>Userland interfaces</title>
+    <para>
+      The DRM core exports several interfaces to applications,
+      generally intended to be used through corresponding libdrm
+      wrapper functions.  In addition, drivers export device-specific
+      interfaces for use by userspace drivers &amp; device-aware
+      applications through ioctls and sysfs files.
+    </para>
+    <para>
+      External interfaces include: memory mapping, context management,
+      DMA operations, AGP management, vblank control, fence
+      management, memory management, and output management.
+    </para>
+    <para>
+      Cover generic ioctls and sysfs layout here.  We only need high-level
+      info, since man pages should cover the rest.
+    </para>
+  </chapter>
+
+  <!-- API reference -->
+
+  <appendix id="drmDriverApi">
+    <title>DRM Driver API</title>
+    <para>
+      Include auto-generated API reference here (need to reference it
+      from paragraphs above too).
+    </para>
+  </appendix>
+
+</book>