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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
+:c:func:`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 :c:func:`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
+------------------
+
+Driver Features
+~~~~~~~~~~~~~~~
+
+Drivers inform the DRM core about their requirements and supported
+features by setting appropriate flags in the driver_features field.
+Since those flags influence the DRM core behaviour since registration
+time, most of them must be set to registering the :c:type:`struct
+drm_driver <drm_driver>` instance.
+
+u32 driver_features;
+
+DRIVER_USE_AGP
+ Driver uses AGP interface, the DRM core will manage AGP resources.
+
+DRIVER_REQUIRE_AGP
+ Driver needs AGP interface to function. AGP initialization failure
+ will become a fatal error.
+
+DRIVER_PCI_DMA
+ Driver is capable of PCI DMA, mapping of PCI DMA buffers to
+ userspace will be enabled. Deprecated.
+
+DRIVER_SG
+ Driver can perform scatter/gather DMA, allocation and mapping of
+ scatter/gather buffers will be enabled. Deprecated.
+
+DRIVER_HAVE_DMA
+ Driver supports DMA, the userspace DMA API will be supported.
+ Deprecated.
+
+DRIVER_HAVE_IRQ; DRIVER_IRQ_SHARED
+ DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler
+ managed by the DRM Core. The core will support simple IRQ handler
+ installation when the flag is set. The installation process is
+ described in ?.
+
+ DRIVER_IRQ_SHARED indicates whether the device & handler support
+ shared IRQs (note that this is required of PCI drivers).
+
+DRIVER_GEM
+ Driver use the GEM memory manager.
+
+DRIVER_MODESET
+ Driver supports mode setting interfaces (KMS).
+
+DRIVER_PRIME
+ Driver implements DRM PRIME buffer sharing.
+
+DRIVER_RENDER
+ Driver supports dedicated render nodes.
+
+DRIVER_ATOMIC
+ Driver supports atomic properties. In this case the driver must
+ implement appropriate obj->atomic_get_property() vfuncs for any
+ modeset objects with driver specific properties.
+
+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:: drivers/gpu/drm/drm_drv.c
+ :export:
+
+Driver Load
+-----------
+
+IRQ Registration
+~~~~~~~~~~~~~~~~
+
+The DRM core tries to facilitate IRQ handler registration and
+unregistration by providing :c:func:`drm_irq_install()` and
+:c:func:`drm_irq_uninstall()` functions. Those functions only
+support a single interrupt per device, devices that use more than one
+IRQs need to be handled manually.
+
+Managed IRQ Registration
+''''''''''''''''''''''''
+
+:c:func:`drm_irq_install()` starts by calling the irq_preinstall
+driver operation. The operation is optional and must make sure that the
+interrupt will not get fired by clearing all pending interrupt flags or
+disabling the interrupt.
+
+The passed-in IRQ will then be requested by a call to
+:c:func:`request_irq()`. If the DRIVER_IRQ_SHARED driver feature
+flag is set, a shared (IRQF_SHARED) IRQ handler will be requested.
+
+The IRQ handler function must be provided as the mandatory irq_handler
+driver operation. It will get passed directly to
+:c:func:`request_irq()` and thus has the same prototype as all IRQ
+handlers. It will get called with a pointer to the DRM device as the
+second argument.
+
+Finally the function calls the optional irq_postinstall driver
+operation. The operation usually enables interrupts (excluding the
+vblank interrupt, which is enabled separately), but drivers may choose
+to enable/disable interrupts at a different time.
+
+:c:func:`drm_irq_uninstall()` is similarly used to uninstall an
+IRQ handler. It starts by waking up all processes waiting on a vblank
+interrupt to make sure they don't hang, and then calls the optional
+irq_uninstall driver operation. The operation must disable all hardware
+interrupts. Finally the function frees the IRQ by calling
+:c:func:`free_irq()`.
+
+Manual IRQ Registration
+'''''''''''''''''''''''
+
+Drivers that require multiple interrupt handlers can't use the managed
+IRQ registration functions. In that case IRQs must be registered and
+unregistered manually (usually with the :c:func:`request_irq()` and
+:c:func:`free_irq()` functions, or their :c:func:`devm_request_irq()` and
+:c:func:`devm_free_irq()` equivalents).
+
+When manually registering IRQs, drivers must not set the
+DRIVER_HAVE_IRQ driver feature flag, and must not provide the
+irq_handler driver operation. They must set the :c:type:`struct
+drm_device <drm_device>` irq_enabled field to 1 upon
+registration of the IRQs, and clear it to 0 after unregistering the
+IRQs.
+
+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.
+
+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:
+
+.. kernel-doc:: drivers/gpu/drm/drm_platform.c
+ :export:
+
+Open/Close, File Operations and IOCTLs
+======================================
+
+Open and Close
+--------------
+
+Open and close handlers. None of those methods are mandatory::
+
+ int (*firstopen) (struct drm_device *);
+ void (*lastclose) (struct drm_device *);
+ int (*open) (struct drm_device *, struct drm_file *);
+ void (*preclose) (struct drm_device *, struct drm_file *);
+ void (*postclose) (struct drm_device *, struct drm_file *);
+
+The firstopen method is called by the DRM core for legacy UMS (User Mode
+Setting) drivers only when an application opens a device that has no
+other opened file handle. UMS drivers can implement it to acquire device
+resources. KMS drivers can't use the method and must acquire resources
+in the load method instead.
+
+Similarly the lastclose method is called when the last application
+holding a file handle opened on the device closes it, for both UMS and
+KMS drivers. Additionally, the method is also called at module unload
+time or, for hot-pluggable devices, when the device is unplugged. The
+firstopen and lastclose calls can thus be unbalanced.
+
+The open method is called every time the device is opened by an
+application. Drivers can allocate per-file private data in this method
+and store them in the struct :c:type:`struct drm_file
+<drm_file>` driver_priv field. Note that the open method is
+called before firstopen.
+
+The close operation is split into preclose and postclose methods.
+Drivers must stop and cleanup all per-file operations in the preclose
+method. For instance pending vertical blanking and page flip events must
+be cancelled. No per-file operation is allowed on the file handle after
+returning from the preclose method.
+
+Finally the postclose method is called as the last step of the close
+operation, right before calling the lastclose method if no other open
+file handle exists for the device. Drivers that have allocated per-file
+private data in the open method should free it here.
+
+The lastclose method should restore CRTC and plane properties to default
+value, so that a subsequent open of the device will not inherit state
+from the previous user. It can also be used to execute delayed power
+switching state changes, e.g. in conjunction with the :ref:`vga_switcheroo`
+infrastructure. Beyond that KMS drivers should not do any
+further cleanup. Only legacy UMS drivers might need to clean up device
+state so that the vga console or an independent fbdev driver could take
+over.
+
+File Operations
+---------------
+
+.. kernel-doc:: drivers/gpu/drm/drm_fops.c
+ :doc: file operations
+
+.. kernel-doc:: drivers/gpu/drm/drm_fops.c
+ :export:
+
+IOCTLs
+------
+
+struct drm_ioctl_desc \*ioctls; int num_ioctls;
+ Driver-specific ioctls descriptors table.
+
+Driver-specific ioctls numbers start at DRM_COMMAND_BASE. The ioctls
+descriptors table is indexed by the ioctl number offset from the base
+value. Drivers can use the DRM_IOCTL_DEF_DRV() macro to initialize
+the table entries.
+
+::
+
+ DRM_IOCTL_DEF_DRV(ioctl, func, flags)
+
+``ioctl`` is the ioctl name. Drivers must define the DRM_##ioctl and
+DRM_IOCTL_##ioctl macros to the ioctl number offset from
+DRM_COMMAND_BASE and the ioctl number respectively. The first macro is
+private to the device while the second must be exposed to userspace in a
+public header.
+
+``func`` is a pointer to the ioctl handler function compatible with the
+``drm_ioctl_t`` type.
+
+::
+
+ typedef int drm_ioctl_t(struct drm_device *dev, void *data,
+ struct drm_file *file_priv);
+
+``flags`` is a bitmask combination of the following values. It restricts
+how the ioctl is allowed to be called.
+
+- DRM_AUTH - Only authenticated callers allowed
+
+- DRM_MASTER - The ioctl can only be called on the master file handle
+
+- DRM_ROOT_ONLY - Only callers with the SYSADMIN capability allowed
+
+- DRM_CONTROL_ALLOW - The ioctl can only be called on a control
+ device
+
+- DRM_UNLOCKED - The ioctl handler will be called without locking the
+ DRM global mutex. This is the enforced default for kms drivers (i.e.
+ using the DRIVER_MODESET flag) and hence shouldn't be used any more
+ for new drivers.
+
+.. kernel-doc:: drivers/gpu/drm/drm_ioctl.c
+ :export:
+
+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.