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+=============
+DRM Internals
+=============
+
+This chapter documents DRM internals relevant to driver authors and
+developers working to add support for the latest features to existing
+drivers.
+
+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.
+
+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 & fencing, suspend/resume support, and
+DMA services.
+
+Driver Initialization
+=====================
+
+At the core of every DRM driver is a :c:type:`struct drm_driver
+<drm_driver>` structure. Drivers typically statically initialize
+a drm_driver structure, and then pass it to
+drm_dev_alloc() to allocate a device instance. After the
+device instance is fully initialized it can be registered (which makes
+it accessible from userspace) using drm_dev_register().
+
+The :c:type:`struct drm_driver <drm_driver>` 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. We will first go through the :c:type:`struct
+drm_driver <drm_driver>` static information fields, and will
+then describe individual operations in details as they get used in later
+sections.
+
+Driver Information
+------------------
+
+Major, Minor and Patchlevel
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+int major; int minor; int patchlevel;
+The DRM core identifies driver versions by a major, minor and patch
+level triplet. The information is printed to the kernel log at
+initialization time and passed to userspace through the
+DRM_IOCTL_VERSION ioctl.
+
+The major and minor numbers are also used to verify the requested driver
+API version passed to DRM_IOCTL_SET_VERSION. When the driver API
+changes between minor versions, applications can call
+DRM_IOCTL_SET_VERSION to select a specific version of the API. If the
+requested major isn't equal to the driver major, or the requested minor
+is larger than the driver minor, the DRM_IOCTL_SET_VERSION call will
+return an error. Otherwise the driver's set_version() method will be
+called with the requested version.
+
+Name, Description and Date
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+char \*name; char \*desc; char \*date;
+The driver name is printed to the kernel log at initialization time,
+used for IRQ registration and passed to userspace through
+DRM_IOCTL_VERSION.
+
+The driver description is a purely informative string passed to
+userspace through the DRM_IOCTL_VERSION ioctl and otherwise unused by
+the kernel.
+
+The driver date, formatted as YYYYMMDD, is meant to identify the date of
+the latest modification to the driver. However, as most drivers fail to
+update it, its value is mostly useless. The DRM core prints it to the
+kernel log at initialization time and passes it to userspace through the
+DRM_IOCTL_VERSION ioctl.
+
+Device Instance and Driver Handling
+-----------------------------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_drv.c
+   :doc: driver instance overview
+
+.. kernel-doc:: include/drm/drm_device.h
+   :internal:
+
+.. kernel-doc:: include/drm/drm_drv.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_drv.c
+   :export:
+
+Driver Load
+-----------
+
+Component Helper Usage
+~~~~~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/gpu/drm/drm_drv.c
+   :doc: component helper usage recommendations
+
+IRQ Helper Library
+~~~~~~~~~~~~~~~~~~
+
+.. kernel-doc:: drivers/gpu/drm/drm_irq.c
+   :doc: irq helpers
+
+.. kernel-doc:: drivers/gpu/drm/drm_irq.c
+   :export:
+
+Memory Manager Initialization
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Every DRM driver requires a memory manager which must be initialized at
+load time. DRM currently contains two memory managers, the Translation
+Table Manager (TTM) and the Graphics Execution Manager (GEM). This
+document describes the use of the GEM memory manager only. See ? for
+details.
+
+Miscellaneous Device Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Another task that may be necessary for PCI devices 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 behaviour like
+hangs or memory corruption.
+
+Managed Resources
+-----------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_managed.c
+   :doc: managed resources
+
+.. kernel-doc:: drivers/gpu/drm/drm_managed.c
+   :export:
+
+.. kernel-doc:: include/drm/drm_managed.h
+   :internal:
+
+Bus-specific Device Registration and PCI Support
+------------------------------------------------
+
+A number of functions are provided to help with device registration. The
+functions deal with PCI and platform devices respectively and are only
+provided for historical reasons. These are all deprecated and shouldn't
+be used in new drivers. Besides that there's a few helpers for pci
+drivers.
+
+.. kernel-doc:: drivers/gpu/drm/drm_pci.c
+   :export:
+
+Open/Close, File Operations and IOCTLs
+======================================
+
+.. _drm_driver_fops:
+
+File Operations
+---------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_file.c
+   :doc: file operations
+
+.. kernel-doc:: include/drm/drm_file.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_file.c
+   :export:
+
+Misc Utilities
+==============
+
+Printer
+-------
+
+.. kernel-doc:: include/drm/drm_print.h
+   :doc: print
+
+.. kernel-doc:: include/drm/drm_print.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/drm_print.c
+   :export:
+
+Utilities
+---------
+
+.. kernel-doc:: include/drm/drm_util.h
+   :doc: drm utils
+
+.. kernel-doc:: include/drm/drm_util.h
+   :internal:
+
+
+Legacy Support Code
+===================
+
+The section very briefly covers some of the old legacy support code
+which is only used by old DRM drivers which have done a so-called
+shadow-attach to the underlying device instead of registering as a real
+driver. This also includes some of the old generic buffer management and
+command submission code. Do not use any of this in new and modern
+drivers.
+
+Legacy Suspend/Resume
+---------------------
+
+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.
+
+int (\*suspend) (struct drm_device \*, pm_message_t state); int
+(\*resume) (struct drm_device \*);
+Those are legacy suspend and resume methods which *only* work with the
+legacy shadow-attach driver registration functions. New driver should
+use the power management interface provided by their bus type (usually
+through the :c:type:`struct device_driver <device_driver>`
+dev_pm_ops) and set these methods to NULL.
+
+Legacy DMA Services
+-------------------
+
+This should cover how DMA mapping etc. is supported by the core. These
+functions are deprecated and should not be used.