<?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 = &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 &

  	    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 & 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.
  ");
  		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 & 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<->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 & 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>