Merge tag 'media/v6.7-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media

Pull media updates from Mauro Carvalho Chehab:

 - the old V4L2 core videobuf kAPI was finally removed. All media
   drivers should now be using VB2 kAPI

 - new automotive driver: mgb4

 - new platform video driver: npcm-video

 - new sensor driver: mt9m114

 - new TI driver used in conjunction with Cadence CSI2RX IP to bridge
   TI-specific parts

 - ir-rx51 was removed and the N900 DT binding was moved to the
   pwm-ir-tx generic driver

 - drop atomisp-specific ov5693, using the upstream driver instead

 - the camss driver has gained RDI3 support for VFE 17x

 - the atomisp driver now detects ISP2400 or ISP2401 at run time. No
   need to set it up at build time anymore

 - lots of driver fixes, cleanups and improvements

* tag 'media/v6.7-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (377 commits)
  media: nuvoton: VIDEO_NPCM_VCD_ECE should depend on ARCH_NPCM
  media: venus: Fix firmware path for resources
  media: venus: hfi_cmds: Replace one-element array with flex-array member and use __counted_by
  media: venus: hfi_parser: Add check to keep the number of codecs within range
  media: venus: hfi: add checks to handle capabilities from firmware
  media: venus: hfi: fix the check to handle session buffer requirement
  media: venus: hfi: add checks to perform sanity on queue pointers
  media: platform: cadence: select MIPI_DPHY dependency
  media: MAINTAINERS: Fix path for J721E CSI2RX bindings
  media: cec: meson: always include meson sub-directory in Makefile
  media: videobuf2: Fix IS_ERR checking in vb2_dc_put_userptr()
  media: platform: mtk-mdp3: fix uninitialized variable in mdp_path_config()
  media: mediatek: vcodec: using encoder device to alloc/free encoder memory
  media: imx-jpeg: notify source chagne event when the first picture parsed
  media: cx231xx: Use EP5_BUF_SIZE macro
  media: siano: Drop unnecessary error check for debugfs_create_dir/file()
  media: mediatek: vcodec: Handle invalid encoder vsi
  media: aspeed: Drop unnecessary error check for debugfs_create_file()
  Documentation: media: buffer.rst: fix V4L2_BUF_FLAG_PREPARED
  Documentation: media: gen-errors.rst: fix confusing ENOTTY description
  ...

5 files changed, 91 insertions, 523 deletions

diff --git a/Documentation/driver-api/media/camera-sensor.rst b/Documentation/driver-api/media/camera-sensor.rst
index 93f4f2536c250..6456145f96ed0 100644
--- a/Documentation/driver-api/media/camera-sensor.rst
+++ b/Documentation/driver-api/media/camera-sensor.rst
@@ -1,8 +1,14 @@
 .. SPDX-License-Identifier: GPL-2.0
 
+.. _media_writing_camera_sensor_drivers:
+
 Writing camera sensor drivers
 =============================
 
+This document covers the in-kernel APIs only. For the best practices on
+userspace API implementation in camera sensor drivers, please see
+:ref:`media_using_camera_sensor_drivers`.
+
 CSI-2 and parallel (BT.601 and BT.656) busses
 ---------------------------------------------
 
@@ -13,7 +19,7 @@ Handling clocks
 
 Camera sensors have an internal clock tree including a PLL and a number of
 divisors. The clock tree is generally configured by the driver based on a few
-input parameters that are specific to the hardware:: the external clock frequency
+input parameters that are specific to the hardware: the external clock frequency
 and the link frequency. The two parameters generally are obtained from system
 firmware. **No other frequencies should be used in any circumstances.**
 
@@ -32,110 +38,61 @@ can rely on this frequency being used.
 Devicetree
 ~~~~~~~~~~
 
-The currently preferred way to achieve this is using ``assigned-clocks``,
-``assigned-clock-parents`` and ``assigned-clock-rates`` properties. See
-``Documentation/devicetree/bindings/clock/clock-bindings.txt`` for more
-information. The driver then gets the frequency using ``clk_get_rate()``.
+The preferred way to achieve this is using ``assigned-clocks``,
+``assigned-clock-parents`` and ``assigned-clock-rates`` properties. See the
+`clock device tree bindings
+<https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/clock/clock.yaml>`_
+for more information. The driver then gets the frequency using
+``clk_get_rate()``.
 
 This approach has the drawback that there's no guarantee that the frequency
 hasn't been modified directly or indirectly by another driver, or supported by
 the board's clock tree to begin with. Changes to the Common Clock Framework API
 are required to ensure reliability.
 
-Frame size
-----------
-
-There are two distinct ways to configure the frame size produced by camera
-sensors.
-
-Freely configurable camera sensor drivers
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Freely configurable camera sensor drivers expose the device's internal
-processing pipeline as one or more sub-devices with different cropping and
-scaling configurations. The output size of the device is the result of a series
-of cropping and scaling operations from the device's pixel array's size.
-
-An example of such a driver is the CCS driver (see ``drivers/media/i2c/ccs``).
-
-Register list based drivers
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-Register list based drivers generally, instead of able to configure the device
-they control based on user requests, are limited to a number of preset
-configurations that combine a number of different parameters that on hardware
-level are independent. How a driver picks such configuration is based on the
-format set on a source pad at the end of the device's internal pipeline.
-
-Most sensor drivers are implemented this way, see e.g.
-``drivers/media/i2c/imx319.c`` for an example.
-
-Frame interval configuration
-----------------------------
-
-There are two different methods for obtaining possibilities for different frame
-intervals as well as configuring the frame interval. Which one to implement
-depends on the type of the device.
-
-Raw camera sensors
-~~~~~~~~~~~~~~~~~~
-
-Instead of a high level parameter such as frame interval, the frame interval is
-a result of the configuration of a number of camera sensor implementation
-specific parameters. Luckily, these parameters tend to be the same for more or
-less all modern raw camera sensors.
-
-The frame interval is calculated using the following equation::
-
-	frame interval = (analogue crop width + horizontal blanking) *
-			 (analogue crop height + vertical blanking) / pixel rate
-
-The formula is bus independent and is applicable for raw timing parameters on
-large variety of devices beyond camera sensors. Devices that have no analogue
-crop, use the full source image size, i.e. pixel array size.
-
-Horizontal and vertical blanking are specified by ``V4L2_CID_HBLANK`` and
-``V4L2_CID_VBLANK``, respectively. The unit of the ``V4L2_CID_HBLANK`` control
-is pixels and the unit of the ``V4L2_CID_VBLANK`` is lines. The pixel rate in
-the sensor's **pixel array** is specified by ``V4L2_CID_PIXEL_RATE`` in the same
-sub-device. The unit of that control is pixels per second.
-
-Register list based drivers need to implement read-only sub-device nodes for the
-purpose. Devices that are not register list based need these to configure the
-device's internal processing pipeline.
-
-The first entity in the linear pipeline is the pixel array. The pixel array may
-be followed by other entities that are there to allow configuring binning,
-skipping, scaling or digital crop :ref:`v4l2-subdev-selections`.
-
-USB cameras etc. devices
-~~~~~~~~~~~~~~~~~~~~~~~~
-
-USB video class hardware, as well as many cameras offering a similar higher
-level interface natively, generally use the concept of frame interval (or frame
-rate) on device level in firmware or hardware. This means lower level controls
-implemented by raw cameras may not be used on uAPI (or even kAPI) to control the
-frame interval on these devices.
-
 Power management
 ----------------
 
-Always use runtime PM to manage the power states of your device. Camera sensor
-drivers are in no way special in this respect: they are responsible for
-controlling the power state of the device they otherwise control as well. In
-general, the device must be powered on at least when its registers are being
-accessed and when it is streaming.
-
-Existing camera sensor drivers may rely on the old
-struct v4l2_subdev_core_ops->s_power() callback for bridge or ISP drivers to
-manage their power state. This is however **deprecated**. If you feel you need
-to begin calling an s_power from an ISP or a bridge driver, instead please add
-runtime PM support to the sensor driver you are using. Likewise, new drivers
-should not use s_power.
-
-Please see examples in e.g. ``drivers/media/i2c/ov8856.c`` and
-``drivers/media/i2c/ccs/ccs-core.c``. The two drivers work in both ACPI
-and DT based systems.
+Camera sensors are used in conjunction with other devices to form a camera
+pipeline. They must obey the rules listed herein to ensure coherent power
+management over the pipeline.
+
+Camera sensor drivers are responsible for controlling the power state of the
+device they otherwise control as well. They shall use runtime PM to manage
+power states. Runtime PM shall be enabled at probe time and disabled at remove
+time. Drivers should enable runtime PM autosuspend.
+
+The runtime PM handlers shall handle clocks, regulators, GPIOs, and other
+system resources required to power the sensor up and down. For drivers that
+don't use any of those resources (such as drivers that support ACPI systems
+only), the runtime PM handlers may be left unimplemented.
+
+In general, the device shall be powered on at least when its registers are
+being accessed and when it is streaming. Drivers should use
+``pm_runtime_resume_and_get()`` when starting streaming and
+``pm_runtime_put()`` or ``pm_runtime_put_autosuspend()`` when stopping
+streaming. They may power the device up at probe time (for example to read
+identification registers), but should not keep it powered unconditionally after
+probe.
+
+At system suspend time, the whole camera pipeline must stop streaming, and
+restart when the system is resumed. This requires coordination between the
+camera sensor and the rest of the camera pipeline. Bridge drivers are
+responsible for this coordination, and instruct camera sensors to stop and
+restart streaming by calling the appropriate subdev operations
+(``.s_stream()``, ``.enable_streams()`` or ``.disable_streams()``). Camera
+sensor drivers shall therefore **not** keep track of the streaming state to
+stop streaming in the PM suspend handler and restart it in the resume handler.
+Drivers should in general not implement the system PM handlers.
+
+Camera sensor drivers shall **not** implement the subdev ``.s_power()``
+operation, as it is deprecated. While this operation is implemented in some
+existing drivers as they predate the deprecation, new drivers shall use runtime
+PM instead. If you feel you need to begin calling ``.s_power()`` from an ISP or
+a bridge driver, instead add runtime PM support to the sensor driver you are
+using and drop its ``.s_power()`` handler.
+
+Please also see :ref:`examples <media-camera-sensor-examples>`.
 
 Control framework
 ~~~~~~~~~~~~~~~~~
@@ -155,21 +112,36 @@ access the device.
 Rotation, orientation and flipping
 ----------------------------------
 
-Some systems have the camera sensor mounted upside down compared to its natural
-mounting rotation. In such cases, drivers shall expose the information to
-userspace with the :ref:`V4L2_CID_CAMERA_SENSOR_ROTATION
-<v4l2-camera-sensor-rotation>` control.
-
-Sensor drivers shall also report the sensor's mounting orientation with the
-:ref:`V4L2_CID_CAMERA_SENSOR_ORIENTATION <v4l2-camera-sensor-orientation>`.
-
 Use ``v4l2_fwnode_device_parse()`` to obtain rotation and orientation
 information from system firmware and ``v4l2_ctrl_new_fwnode_properties()`` to
 register the appropriate controls.
 
-Sensor drivers that have any vertical or horizontal flips embedded in the
-register programming sequences shall initialize the V4L2_CID_HFLIP and
-V4L2_CID_VFLIP controls with the values programmed by the register sequences.
-The default values of these controls shall be 0 (disabled). Especially these
-controls shall not be inverted, independently of the sensor's mounting
-rotation.
+.. _media-camera-sensor-examples:
+
+Example drivers
+---------------
+
+Features implemented by sensor drivers vary, and depending on the set of
+supported features and other qualities, particular sensor drivers better serve
+the purpose of an example. The following drivers are known to be good examples:
+
+.. flat-table:: Example sensor drivers
+    :header-rows: 0
+    :widths:      1 1 1 2
+
+    * - Driver name
+      - File(s)
+      - Driver type
+      - Example topic
+    * - CCS
+      - ``drivers/media/i2c/ccs/``
+      - Freely configurable
+      - Power management (ACPI and DT), UAPI
+    * - imx219
+      - ``drivers/media/i2c/imx219.c``
+      - Register list based
+      - Power management (DT), UAPI, mode selection
+    * - imx319
+      - ``drivers/media/i2c/imx319.c``
+      - Register list based
+      - Power management (ACPI and DT)
diff --git a/Documentation/driver-api/media/drivers/ccs/ccs.rst b/Documentation/driver-api/media/drivers/ccs/ccs.rst
index 7389204afcb82..776eec72bc80a 100644
--- a/Documentation/driver-api/media/drivers/ccs/ccs.rst
+++ b/Documentation/driver-api/media/drivers/ccs/ccs.rst
@@ -30,7 +30,7 @@ that purpose, selection target ``V4L2_SEL_TGT_COMPOSE`` is supported on the
 sink pad (0).
 
 Additionally, if a device has no scaler or digital crop functionality, the
-source pad (1) expses another digital crop selection rectangle that can only
+source pad (1) exposes another digital crop selection rectangle that can only
 crop at the end of the lines and frames.
 
 Scaler
@@ -78,6 +78,14 @@ For SMIA (non-++) compliant devices the static data file name is
 vvvv or vv denotes MIPI and SMIA manufacturer IDs respectively, mmmm model ID
 and rrrr or rr revision number.
 
+CCS tools
+~~~~~~~~~
+
+`CCS tools <https://github.com/MIPI-Alliance/ccs-tools/>`_ is a set of
+tools for working with CCS static data files. CCS tools includes a
+definition of the human-readable CCS static data YAML format and includes a
+program to convert it to a binary.
+
 Register definition generator
 -----------------------------
 
diff --git a/Documentation/driver-api/media/v4l2-core.rst b/Documentation/driver-api/media/v4l2-core.rst
index 239045ecc8f42..58cba831ade5a 100644
--- a/Documentation/driver-api/media/v4l2-core.rst
+++ b/Documentation/driver-api/media/v4l2-core.rst
@@ -13,7 +13,6 @@ Video4Linux devices
     v4l2-subdev
     v4l2-event
     v4l2-controls
-    v4l2-videobuf
     v4l2-videobuf2
     v4l2-dv-timings
     v4l2-flash-led-class
diff --git a/Documentation/driver-api/media/v4l2-dev.rst b/Documentation/driver-api/media/v4l2-dev.rst
index 99e3b5fa74447..d5cb19b21a9f7 100644
--- a/Documentation/driver-api/media/v4l2-dev.rst
+++ b/Documentation/driver-api/media/v4l2-dev.rst
@@ -157,14 +157,6 @@ changing the e.g. exposure of the webcam.
 Of course, you can always do all the locking yourself by leaving both lock
 pointers at ``NULL``.
 
-If you use the old :ref:`videobuf framework <vb_framework>` then you must
-pass the :c:type:`video_device`->lock to the videobuf queue initialize
-function: if videobuf has to wait for a frame to arrive, then it will
-temporarily unlock the lock and relock it afterwards. If your driver also
-waits in the code, then you should do the same to allow other
-processes to access the device node while the first process is waiting for
-something.
-
 In the case of :ref:`videobuf2 <vb2_framework>` you will need to implement the
 ``wait_prepare()`` and ``wait_finish()`` callbacks to unlock/lock if applicable.
 If you use the ``queue->lock`` pointer, then you can use the helper functions
diff --git a/Documentation/driver-api/media/v4l2-videobuf.rst b/Documentation/driver-api/media/v4l2-videobuf.rst
deleted file mode 100644
index 4b1d84eefeb8b..0000000000000
--- a/Documentation/driver-api/media/v4l2-videobuf.rst
+++ /dev/null
@@ -1,403 +0,0 @@
-.. SPDX-License-Identifier: GPL-2.0
-
-.. _vb_framework:
-
-Videobuf Framework
-==================
-
-Author: Jonathan Corbet <corbet@lwn.net>
-
-Current as of 2.6.33
-
-.. note::
-
-   The videobuf framework was deprecated in favor of videobuf2. Shouldn't
-   be used on new drivers.
-
-Introduction
-------------
-
-The videobuf layer functions as a sort of glue layer between a V4L2 driver
-and user space.  It handles the allocation and management of buffers for
-the storage of video frames.  There is a set of functions which can be used
-to implement many of the standard POSIX I/O system calls, including read(),
-poll(), and, happily, mmap().  Another set of functions can be used to
-implement the bulk of the V4L2 ioctl() calls related to streaming I/O,
-including buffer allocation, queueing and dequeueing, and streaming
-control.  Using videobuf imposes a few design decisions on the driver
-author, but the payback comes in the form of reduced code in the driver and
-a consistent implementation of the V4L2 user-space API.
-
-Buffer types
-------------
-
-Not all video devices use the same kind of buffers.  In fact, there are (at
-least) three common variations:
-
- - Buffers which are scattered in both the physical and (kernel) virtual
-   address spaces.  (Almost) all user-space buffers are like this, but it
-   makes great sense to allocate kernel-space buffers this way as well when
-   it is possible.  Unfortunately, it is not always possible; working with
-   this kind of buffer normally requires hardware which can do
-   scatter/gather DMA operations.
-
- - Buffers which are physically scattered, but which are virtually
-   contiguous; buffers allocated with vmalloc(), in other words.  These
-   buffers are just as hard to use for DMA operations, but they can be
-   useful in situations where DMA is not available but virtually-contiguous
-   buffers are convenient.
-
- - Buffers which are physically contiguous.  Allocation of this kind of
-   buffer can be unreliable on fragmented systems, but simpler DMA
-   controllers cannot deal with anything else.
-
-Videobuf can work with all three types of buffers, but the driver author
-must pick one at the outset and design the driver around that decision.
-
-[It's worth noting that there's a fourth kind of buffer: "overlay" buffers
-which are located within the system's video memory.  The overlay
-functionality is considered to be deprecated for most use, but it still
-shows up occasionally in system-on-chip drivers where the performance
-benefits merit the use of this technique.  Overlay buffers can be handled
-as a form of scattered buffer, but there are very few implementations in
-the kernel and a description of this technique is currently beyond the
-scope of this document.]
-
-Data structures, callbacks, and initialization
-----------------------------------------------
-
-Depending on which type of buffers are being used, the driver should
-include one of the following files:
-
-.. code-block:: none
-
-    <media/videobuf-dma-sg.h>		/* Physically scattered */
-    <media/videobuf-vmalloc.h>		/* vmalloc() buffers	*/
-    <media/videobuf-dma-contig.h>	/* Physically contiguous */
-
-The driver's data structure describing a V4L2 device should include a
-struct videobuf_queue instance for the management of the buffer queue,
-along with a list_head for the queue of available buffers.  There will also
-need to be an interrupt-safe spinlock which is used to protect (at least)
-the queue.
-
-The next step is to write four simple callbacks to help videobuf deal with
-the management of buffers:
-
-.. code-block:: none
-
-    struct videobuf_queue_ops {
-	int (*buf_setup)(struct videobuf_queue *q,
-			 unsigned int *count, unsigned int *size);
-	int (*buf_prepare)(struct videobuf_queue *q,
-			   struct videobuf_buffer *vb,
-			   enum v4l2_field field);
-	void (*buf_queue)(struct videobuf_queue *q,
-			  struct videobuf_buffer *vb);
-	void (*buf_release)(struct videobuf_queue *q,
-			    struct videobuf_buffer *vb);
-    };
-
-buf_setup() is called early in the I/O process, when streaming is being
-initiated; its purpose is to tell videobuf about the I/O stream.  The count
-parameter will be a suggested number of buffers to use; the driver should
-check it for rationality and adjust it if need be.  As a practical rule, a
-minimum of two buffers are needed for proper streaming, and there is
-usually a maximum (which cannot exceed 32) which makes sense for each
-device.  The size parameter should be set to the expected (maximum) size
-for each frame of data.
-
-Each buffer (in the form of a struct videobuf_buffer pointer) will be
-passed to buf_prepare(), which should set the buffer's size, width, height,
-and field fields properly.  If the buffer's state field is
-VIDEOBUF_NEEDS_INIT, the driver should pass it to:
-
-.. code-block:: none
-
-    int videobuf_iolock(struct videobuf_queue* q, struct videobuf_buffer *vb,
-			struct v4l2_framebuffer *fbuf);
-
-Among other things, this call will usually allocate memory for the buffer.
-Finally, the buf_prepare() function should set the buffer's state to
-VIDEOBUF_PREPARED.
-
-When a buffer is queued for I/O, it is passed to buf_queue(), which should
-put it onto the driver's list of available buffers and set its state to
-VIDEOBUF_QUEUED.  Note that this function is called with the queue spinlock
-held; if it tries to acquire it as well things will come to a screeching
-halt.  Yes, this is the voice of experience.  Note also that videobuf may
-wait on the first buffer in the queue; placing other buffers in front of it
-could again gum up the works.  So use list_add_tail() to enqueue buffers.
-
-Finally, buf_release() is called when a buffer is no longer intended to be
-used.  The driver should ensure that there is no I/O active on the buffer,
-then pass it to the appropriate free routine(s):
-
-.. code-block:: none
-
-    /* Scatter/gather drivers */
-    int videobuf_dma_unmap(struct videobuf_queue *q,
-			   struct videobuf_dmabuf *dma);
-    int videobuf_dma_free(struct videobuf_dmabuf *dma);
-
-    /* vmalloc drivers */
-    void videobuf_vmalloc_free (struct videobuf_buffer *buf);
-
-    /* Contiguous drivers */
-    void videobuf_dma_contig_free(struct videobuf_queue *q,
-				  struct videobuf_buffer *buf);
-
-One way to ensure that a buffer is no longer under I/O is to pass it to:
-
-.. code-block:: none
-
-    int videobuf_waiton(struct videobuf_buffer *vb, int non_blocking, int intr);
-
-Here, vb is the buffer, non_blocking indicates whether non-blocking I/O
-should be used (it should be zero in the buf_release() case), and intr
-controls whether an interruptible wait is used.
-
-File operations
----------------
-
-At this point, much of the work is done; much of the rest is slipping
-videobuf calls into the implementation of the other driver callbacks.  The
-first step is in the open() function, which must initialize the
-videobuf queue.  The function to use depends on the type of buffer used:
-
-.. code-block:: none
-
-    void videobuf_queue_sg_init(struct videobuf_queue *q,
-				struct videobuf_queue_ops *ops,
-				struct device *dev,
-				spinlock_t *irqlock,
-				enum v4l2_buf_type type,
-				enum v4l2_field field,
-				unsigned int msize,
-				void *priv);
-
-    void videobuf_queue_vmalloc_init(struct videobuf_queue *q,
-				struct videobuf_queue_ops *ops,
-				struct device *dev,
-				spinlock_t *irqlock,
-				enum v4l2_buf_type type,
-				enum v4l2_field field,
-				unsigned int msize,
-				void *priv);
-
-    void videobuf_queue_dma_contig_init(struct videobuf_queue *q,
-				       struct videobuf_queue_ops *ops,
-				       struct device *dev,
-				       spinlock_t *irqlock,
-				       enum v4l2_buf_type type,
-				       enum v4l2_field field,
-				       unsigned int msize,
-				       void *priv);
-
-In each case, the parameters are the same: q is the queue structure for the
-device, ops is the set of callbacks as described above, dev is the device
-structure for this video device, irqlock is an interrupt-safe spinlock to
-protect access to the data structures, type is the buffer type used by the
-device (cameras will use V4L2_BUF_TYPE_VIDEO_CAPTURE, for example), field
-describes which field is being captured (often V4L2_FIELD_NONE for
-progressive devices), msize is the size of any containing structure used
-around struct videobuf_buffer, and priv is a private data pointer which
-shows up in the priv_data field of struct videobuf_queue.  Note that these
-are void functions which, evidently, are immune to failure.
-
-V4L2 capture drivers can be written to support either of two APIs: the
-read() system call and the rather more complicated streaming mechanism.  As
-a general rule, it is necessary to support both to ensure that all
-applications have a chance of working with the device.  Videobuf makes it
-easy to do that with the same code.  To implement read(), the driver need
-only make a call to one of:
-
-.. code-block:: none
-
-    ssize_t videobuf_read_one(struct videobuf_queue *q,
-			      char __user *data, size_t count,
-			      loff_t *ppos, int nonblocking);
-
-    ssize_t videobuf_read_stream(struct videobuf_queue *q,
-				 char __user *data, size_t count,
-				 loff_t *ppos, int vbihack, int nonblocking);
-
-Either one of these functions will read frame data into data, returning the
-amount actually read; the difference is that videobuf_read_one() will only
-read a single frame, while videobuf_read_stream() will read multiple frames
-if they are needed to satisfy the count requested by the application.  A
-typical driver read() implementation will start the capture engine, call
-one of the above functions, then stop the engine before returning (though a
-smarter implementation might leave the engine running for a little while in
-anticipation of another read() call happening in the near future).
-
-The poll() function can usually be implemented with a direct call to:
-
-.. code-block:: none
-
-    unsigned int videobuf_poll_stream(struct file *file,
-				      struct videobuf_queue *q,
-				      poll_table *wait);
-
-Note that the actual wait queue eventually used will be the one associated
-with the first available buffer.
-
-When streaming I/O is done to kernel-space buffers, the driver must support
-the mmap() system call to enable user space to access the data.  In many
-V4L2 drivers, the often-complex mmap() implementation simplifies to a
-single call to:
-
-.. code-block:: none
-
-    int videobuf_mmap_mapper(struct videobuf_queue *q,
-			     struct vm_area_struct *vma);
-
-Everything else is handled by the videobuf code.
-
-The release() function requires two separate videobuf calls:
-
-.. code-block:: none
-
-    void videobuf_stop(struct videobuf_queue *q);
-    int videobuf_mmap_free(struct videobuf_queue *q);
-
-The call to videobuf_stop() terminates any I/O in progress - though it is
-still up to the driver to stop the capture engine.  The call to
-videobuf_mmap_free() will ensure that all buffers have been unmapped; if
-so, they will all be passed to the buf_release() callback.  If buffers
-remain mapped, videobuf_mmap_free() returns an error code instead.  The
-purpose is clearly to cause the closing of the file descriptor to fail if
-buffers are still mapped, but every driver in the 2.6.32 kernel cheerfully
-ignores its return value.
-
-ioctl() operations
-------------------
-
-The V4L2 API includes a very long list of driver callbacks to respond to
-the many ioctl() commands made available to user space.  A number of these
-- those associated with streaming I/O - turn almost directly into videobuf
-calls.  The relevant helper functions are:
-
-.. code-block:: none
-
-    int videobuf_reqbufs(struct videobuf_queue *q,
-			 struct v4l2_requestbuffers *req);
-    int videobuf_querybuf(struct videobuf_queue *q, struct v4l2_buffer *b);
-    int videobuf_qbuf(struct videobuf_queue *q, struct v4l2_buffer *b);
-    int videobuf_dqbuf(struct videobuf_queue *q, struct v4l2_buffer *b,
-		       int nonblocking);
-    int videobuf_streamon(struct videobuf_queue *q);
-    int videobuf_streamoff(struct videobuf_queue *q);
-
-So, for example, a VIDIOC_REQBUFS call turns into a call to the driver's
-vidioc_reqbufs() callback which, in turn, usually only needs to locate the
-proper struct videobuf_queue pointer and pass it to videobuf_reqbufs().
-These support functions can replace a great deal of buffer management
-boilerplate in a lot of V4L2 drivers.
-
-The vidioc_streamon() and vidioc_streamoff() functions will be a bit more
-complex, of course, since they will also need to deal with starting and
-stopping the capture engine.
-
-Buffer allocation
------------------
-
-Thus far, we have talked about buffers, but have not looked at how they are
-allocated.  The scatter/gather case is the most complex on this front.  For
-allocation, the driver can leave buffer allocation entirely up to the
-videobuf layer; in this case, buffers will be allocated as anonymous
-user-space pages and will be very scattered indeed.  If the application is
-using user-space buffers, no allocation is needed; the videobuf layer will
-take care of calling get_user_pages() and filling in the scatterlist array.
-
-If the driver needs to do its own memory allocation, it should be done in
-the vidioc_reqbufs() function, *after* calling videobuf_reqbufs().  The
-first step is a call to:
-
-.. code-block:: none
-
-    struct videobuf_dmabuf *videobuf_to_dma(struct videobuf_buffer *buf);
-
-The returned videobuf_dmabuf structure (defined in
-<media/videobuf-dma-sg.h>) includes a couple of relevant fields:
-
-.. code-block:: none
-
-    struct scatterlist  *sglist;
-    int                 sglen;
-
-The driver must allocate an appropriately-sized scatterlist array and
-populate it with pointers to the pieces of the allocated buffer; sglen
-should be set to the length of the array.
-
-Drivers using the vmalloc() method need not (and cannot) concern themselves
-with buffer allocation at all; videobuf will handle those details.  The
-same is normally true of contiguous-DMA drivers as well; videobuf will
-allocate the buffers (with dma_alloc_coherent()) when it sees fit.  That
-means that these drivers may be trying to do high-order allocations at any
-time, an operation which is not always guaranteed to work.  Some drivers
-play tricks by allocating DMA space at system boot time; videobuf does not
-currently play well with those drivers.
-
-As of 2.6.31, contiguous-DMA drivers can work with a user-supplied buffer,
-as long as that buffer is physically contiguous.  Normal user-space
-allocations will not meet that criterion, but buffers obtained from other
-kernel drivers, or those contained within huge pages, will work with these
-drivers.
-
-Filling the buffers
--------------------
-
-The final part of a videobuf implementation has no direct callback - it's
-the portion of the code which actually puts frame data into the buffers,
-usually in response to interrupts from the device.  For all types of
-drivers, this process works approximately as follows:
-
- - Obtain the next available buffer and make sure that somebody is actually
-   waiting for it.
-
- - Get a pointer to the memory and put video data there.
-
- - Mark the buffer as done and wake up the process waiting for it.
-
-Step (1) above is done by looking at the driver-managed list_head structure
-- the one which is filled in the buf_queue() callback.  Because starting
-the engine and enqueueing buffers are done in separate steps, it's possible
-for the engine to be running without any buffers available - in the
-vmalloc() case especially.  So the driver should be prepared for the list
-to be empty.  It is equally possible that nobody is yet interested in the
-buffer; the driver should not remove it from the list or fill it until a
-process is waiting on it.  That test can be done by examining the buffer's
-done field (a wait_queue_head_t structure) with waitqueue_active().
-
-A buffer's state should be set to VIDEOBUF_ACTIVE before being mapped for
-DMA; that ensures that the videobuf layer will not try to do anything with
-it while the device is transferring data.
-
-For scatter/gather drivers, the needed memory pointers will be found in the
-scatterlist structure described above.  Drivers using the vmalloc() method
-can get a memory pointer with:
-
-.. code-block:: none
-
-    void *videobuf_to_vmalloc(struct videobuf_buffer *buf);
-
-For contiguous DMA drivers, the function to use is:
-
-.. code-block:: none
-
-    dma_addr_t videobuf_to_dma_contig(struct videobuf_buffer *buf);
-
-The contiguous DMA API goes out of its way to hide the kernel-space address
-of the DMA buffer from drivers.
-
-The final step is to set the size field of the relevant videobuf_buffer
-structure to the actual size of the captured image, set state to
-VIDEOBUF_DONE, then call wake_up() on the done queue.  At this point, the
-buffer is owned by the videobuf layer and the driver should not touch it
-again.
-
-Developers who are interested in more information can go into the relevant
-header files; there are a few low-level functions declared there which have
-not been talked about here.  Note also that all of these calls are exported
-GPL-only, so they will not be available to non-GPL kernel modules.