7 files changed, 438 insertions, 103 deletions

diff --git a/Documentation/video4linux/CARDLIST.cx23885 b/Documentation/video4linux/CARDLIST.cx23885
index 7539e8fa1ffd..16ca030e1185 100644
--- a/Documentation/video4linux/CARDLIST.cx23885
+++ b/Documentation/video4linux/CARDLIST.cx23885
@@ -26,3 +26,4 @@
  25 -> Compro VideoMate E800                               [1858:e800]
  26 -> Hauppauge WinTV-HVR1290                             [0070:8551]
  27 -> Mygica X8558 PRO DMB-TH                             [14f1:8578]
+ 28 -> LEADTEK WinFast PxTV1200                            [107d:6f22]
diff --git a/Documentation/video4linux/CARDLIST.saa7134 b/Documentation/video4linux/CARDLIST.saa7134
index fce1e7eb0474..b4a767060ed7 100644
--- a/Documentation/video4linux/CARDLIST.saa7134
+++ b/Documentation/video4linux/CARDLIST.saa7134
@@ -174,3 +174,4 @@
 173 -> Zolid Hybrid TV Tuner PCI                [1131:2004]
 174 -> Asus Europa Hybrid OEM                   [1043:4847]
 175 -> Leadtek Winfast DTV1000S                 [107d:6655]
+176 -> Beholder BeholdTV 505 RDS                [0000:5051]
diff --git a/Documentation/video4linux/CARDLIST.tuner b/Documentation/video4linux/CARDLIST.tuner
index e0d298fe8830..9b2e0dd6017e 100644
--- a/Documentation/video4linux/CARDLIST.tuner
+++ b/Documentation/video4linux/CARDLIST.tuner
@@ -81,3 +81,4 @@ tuner=80 - Philips FQ1216LME MK3 PAL/SECAM w/active loopthrough
 tuner=81 - Partsnic (Daewoo) PTI-5NF05
 tuner=82 - Philips CU1216L
 tuner=83 - NXP TDA18271
+tuner=84 - Sony BTF-Pxn01Z
diff --git a/Documentation/video4linux/README.tlg2300 b/Documentation/video4linux/README.tlg2300
new file mode 100644
index 000000000000..416ccb93d8c9
--- /dev/null
+++ b/Documentation/video4linux/README.tlg2300
@@ -0,0 +1,47 @@
+tlg2300 release notes
+====================
+
+This is a v4l2/dvb device driver for the tlg2300 chip.
+
+
+current status
+==============
+
+video
+        - support mmap and read().(no overlay)
+
+audio
+        - The driver will register a ALSA card for the audio input.
+
+vbi
+        - Works for almost TV norms.
+
+dvb-t
+        - works for DVB-T
+
+FM
+        - Works for radio.
+
+---------------------------------------------------------------------------
+TESTED APPLICATIONS:
+
+-VLC1.0.4 test the video and dvb. The GUI is friendly to use.
+
+-Mplayer test the video.
+
+-Mplayer test the FM. The mplayer should be compiled with --enable-radio and
+         --enable-radio-capture.
+        The command runs as this(The alsa audio registers to card 1):
+        #mplayer radio://103.7/capture/ -radio adevice=hw=1,0:arate=48000 \
+                -rawaudio rate=48000:channels=2
+
+---------------------------------------------------------------------------
+KNOWN PROBLEMS:
+about preemphasis:
+        You can set the preemphasis for radio by the following command:
+        #v4l2-ctl -d /dev/radio0 --set-ctrl=pre_emphasis_settings=1
+
+        "pre_emphasis_settings=1" means that you select the 50us. If you want
+        to select the 75us, please use "pre_emphasis_settings=2"
+
+
diff --git a/Documentation/video4linux/gspca.txt b/Documentation/video4linux/gspca.txt
index 1800a62cf135..181b9e6fd984 100644
--- a/Documentation/video4linux/gspca.txt
+++ b/Documentation/video4linux/gspca.txt
@@ -42,6 +42,7 @@ ov519		041e:4064	Creative Live! VISTA VF0420
 ov519           041e:4067       Creative Live! Cam Video IM (VF0350)
 ov519           041e:4068       Creative Live! VISTA VF0470
 spca561         0458:7004       Genius VideoCAM Express V2
+sn9c2028        0458:7005       Genius Smart 300, version 2
 sunplus         0458:7006       Genius Dsc 1.3 Smart
 zc3xx           0458:7007       Genius VideoCam V2
 zc3xx           0458:700c       Genius VideoCam V3
@@ -109,6 +110,7 @@ sunplus		04a5:3003	Benq DC 1300
 sunplus         04a5:3008       Benq DC 1500
 sunplus         04a5:300a       Benq DC 3410
 spca500         04a5:300c       Benq DC 1016
+benq            04a5:3035       Benq DC E300
 finepix         04cb:0104       Fujifilm FinePix 4800
 finepix         04cb:0109       Fujifilm FinePix A202
 finepix         04cb:010b       Fujifilm FinePix A203
@@ -142,6 +144,7 @@ sunplus		04fc:5360	Sunplus Generic
 spca500         04fc:7333       PalmPixDC85
 sunplus         04fc:ffff       Pure DigitalDakota
 spca501         0506:00df       3Com HomeConnect Lite
+sunplus         052b:1507       Megapixel 5 Pretec DC-1007
 sunplus         052b:1513       Megapix V4
 sunplus         052b:1803       MegaImage VI
 tv8532          0545:808b       Veo Stingray
@@ -151,6 +154,7 @@ sunplus		0546:3191	Polaroid Ion 80
 sunplus         0546:3273       Polaroid PDC2030
 ov519           054c:0154       Sonny toy4
 ov519           054c:0155       Sonny toy5
+cpia1           0553:0002       CPIA CPiA (version1) based cameras
 zc3xx           055f:c005       Mustek Wcam300A
 spca500         055f:c200       Mustek Gsmart 300
 sunplus         055f:c211       Kowa Bs888e Microcamera
@@ -188,8 +192,7 @@ spca500		06bd:0404	Agfa CL20
 spca500         06be:0800       Optimedia
 sunplus         06d6:0031       Trust 610 LCD PowerC@m Zoom
 spca506         06e1:a190       ADS Instant VCD
-ov534           06f8:3002       Hercules Blog Webcam
-ov534           06f8:3003       Hercules Dualpix HD Weblog
+ov534_9         06f8:3003       Hercules Dualpix HD Weblog
 sonixj          06f8:3004       Hercules Classic Silver
 sonixj          06f8:3008       Hercules Deluxe Optical Glass
 pac7302         06f8:3009       Hercules Classic Link
@@ -204,6 +207,7 @@ sunplus		0733:2221	Mercury Digital Pro 3.1p
 sunplus         0733:3261       Concord 3045 spca536a
 sunplus         0733:3281       Cyberpix S550V
 spca506         0734:043b       3DeMon USB Capture aka
+cpia1           0813:0001       QX3 camera
 ov519           0813:0002       Dual Mode USB Camera Plus
 spca500         084d:0003       D-Link DSC-350
 spca500         08ca:0103       Aiptek PocketDV
@@ -225,7 +229,8 @@ sunplus		08ca:2050	Medion MD 41437
 sunplus         08ca:2060       Aiptek PocketDV5300
 tv8532          0923:010f       ICM532 cams
 mars            093a:050f       Mars-Semi Pc-Camera
-mr97310a        093a:010f       Sakar Digital no. 77379
+mr97310a        093a:010e       All known CIF cams with this ID
+mr97310a        093a:010f       All known VGA cams with this ID
 pac207          093a:2460       Qtec Webcam 100
 pac207          093a:2461       HP Webcam
 pac207          093a:2463       Philips SPC 220 NC
@@ -302,6 +307,7 @@ sonixj		0c45:613b	Surfer SN-206
 sonixj          0c45:613c       Sonix Pccam168
 sonixj          0c45:6143       Sonix Pccam168
 sonixj          0c45:6148       Digitus DA-70811/ZSMC USB PC Camera ZS211/Microdia
+sonixj          0c45:614a       Frontech E-Ccam (JIL-2225)
 sn9c20x         0c45:6240       PC Camera (SN9C201 + MT9M001)
 sn9c20x         0c45:6242       PC Camera (SN9C201 + MT9M111)
 sn9c20x         0c45:6248       PC Camera (SN9C201 + OV9655)
@@ -324,6 +330,10 @@ sn9c20x		0c45:62b0	PC Camera (SN9C202 + MT9V011/MT9V111/MT9V112)
 sn9c20x         0c45:62b3       PC Camera (SN9C202 + OV9655)
 sn9c20x         0c45:62bb       PC Camera (SN9C202 + OV7660)
 sn9c20x         0c45:62bc       PC Camera (SN9C202 + HV7131R)
+sn9c2028        0c45:8001       Wild Planet Digital Spy Camera
+sn9c2028        0c45:8003       Sakar #11199, #6637x, #67480 keychain cams
+sn9c2028        0c45:8008       Mini-Shotz ms-350
+sn9c2028        0c45:800a       Vivitar Vivicam 3350B
 sunplus         0d64:0303       Sunplus FashionCam DXG
 ov519           0e96:c001       TRUST 380 USB2 SPACEC@M
 etoms           102c:6151       Qcam Sangha CIF
@@ -341,10 +351,11 @@ spca501		1776:501c	Arowana 300K CMOS Camera
 t613            17a1:0128       TASCORP JPEG Webcam, NGS Cyclops
 vc032x          17ef:4802       Lenovo Vc0323+MI1310_SOC
 pac207          2001:f115       D-Link DSB-C120
-sq905c          2770:9050       sq905c
-sq905c          2770:905c       DualCamera
-sq905           2770:9120       Argus Digital Camera DC1512
-sq905c          2770:913d       sq905c
+sq905c          2770:9050       Disney pix micro (CIF)
+sq905c          2770:9052       Disney pix micro 2 (VGA)
+sq905c          2770:905c       All 11 known cameras with this ID
+sq905           2770:9120       All 24 known cameras with this ID
+sq905c          2770:913d       All 4 known cameras with this ID
 spca500         2899:012c       Toptro Industrial
 ov519           8020:ef04       ov519
 spca508         8086:0110       Intel Easy PC Camera
diff --git a/Documentation/video4linux/v4l2-framework.txt b/Documentation/video4linux/v4l2-framework.txt
index 74d677c8b036..5155700c206b 100644
--- a/Documentation/video4linux/v4l2-framework.txt
+++ b/Documentation/video4linux/v4l2-framework.txt
@@ -599,99 +599,13 @@ video_device::minor fields.
 video buffer helper functions
 -----------------------------
 
-The v4l2 core API provides a standard method for dealing with video
-buffers. Those methods allow a driver to implement read(), mmap() and
-overlay() on a consistent way.
-
-There are currently methods for using video buffers on devices that
-supports DMA with scatter/gather method (videobuf-dma-sg), DMA with
-linear access (videobuf-dma-contig), and vmalloced buffers, mostly
-used on USB drivers (videobuf-vmalloc).
-
-Any driver using videobuf should provide operations (callbacks) for
-four handlers:
-
-ops->buf_setup   - calculates the size of the video buffers and avoid they
-                   to waste more than some maximum limit of RAM;
-ops->buf_prepare - fills the video buffer structs and calls
-                   videobuf_iolock() to alloc and prepare mmaped memory;
-ops->buf_queue   - advices the driver that another buffer were
-                   requested (by read() or by QBUF);
-ops->buf_release - frees any buffer that were allocated.
-
-In order to use it, the driver need to have a code (generally called at
-interrupt context) that will properly handle the buffer request lists,
-announcing that a new buffer were filled.
-
-The irq handling code should handle the videobuf task lists, in order
-to advice videobuf that a new frame were filled, in order to honor to a
-request. The code is generally like this one:
-        if (list_empty(&dma_q->active))
-                return;
-
-        buf = list_entry(dma_q->active.next, struct vbuffer, vb.queue);
-
-        if (!waitqueue_active(&buf->vb.done))
-                return;
-
-        /* Some logic to handle the buf may be needed here */
-
-        list_del(&buf->vb.queue);
-        do_gettimeofday(&buf->vb.ts);
-        wake_up(&buf->vb.done);
-
-Those are the videobuffer functions used on drivers, implemented on
-videobuf-core:
-
-- Videobuf init functions
-  videobuf_queue_sg_init()
-      Initializes the videobuf infrastructure. This function should be
-      called before any other videobuf function on drivers that uses DMA
-      Scatter/Gather buffers.
-
-  videobuf_queue_dma_contig_init
-      Initializes the videobuf infrastructure. This function should be
-      called before any other videobuf function on drivers that need DMA
-      contiguous buffers.
-
-  videobuf_queue_vmalloc_init()
-      Initializes the videobuf infrastructure. This function should be
-      called before any other videobuf function on USB (and other drivers)
-      that need a vmalloced type of videobuf.
-
-- videobuf_iolock()
-  Prepares the videobuf memory for the proper method (read, mmap, overlay).
-
-- videobuf_queue_is_busy()
-  Checks if a videobuf is streaming.
-
-- videobuf_queue_cancel()
-  Stops video handling.
-
-- videobuf_mmap_free()
-  frees mmap buffers.
-
-- videobuf_stop()
-  Stops video handling, ends mmap and frees mmap and other buffers.
-
-- V4L2 api functions. Those functions correspond to VIDIOC_foo ioctls:
-   videobuf_reqbufs(), videobuf_querybuf(), videobuf_qbuf(),
-   videobuf_dqbuf(), videobuf_streamon(), videobuf_streamoff().
-
-- V4L1 api function (corresponds to VIDIOCMBUF ioctl):
-   videobuf_cgmbuf()
-      This function is used to provide backward compatibility with V4L1
-      API.
-
-- Some help functions for read()/poll() operations:
-   videobuf_read_stream()
-      For continuous stream read()
-   videobuf_read_one()
-      For snapshot read()
-   videobuf_poll_stream()
-      polling help function
-
-The better way to understand it is to take a look at vivi driver. One
-of the main reasons for vivi is to be a videobuf usage example. the
-vivi_thread_tick() does the task that the IRQ callback would do on PCI
-drivers (or the irq callback on USB).
+The v4l2 core API provides a set of standard methods (called "videobuf")
+for dealing with video buffers. Those methods allow a driver to implement
+read(), mmap() and overlay() in a consistent way.  There are currently
+methods for using video buffers on devices that supports DMA with
+scatter/gather method (videobuf-dma-sg), DMA with linear access
+(videobuf-dma-contig), and vmalloced buffers, mostly used on USB drivers
+(videobuf-vmalloc).
+
+Please see Documentation/video4linux/videobuf for more information on how
+to use the videobuf layer.
diff --git a/Documentation/video4linux/videobuf b/Documentation/video4linux/videobuf
new file mode 100644
index 000000000000..17a1f9abf260
--- /dev/null
+++ b/Documentation/video4linux/videobuf
@@ -0,0 +1,360 @@
+An introduction to the videobuf layer
+Jonathan Corbet <corbet@lwn.net>
+Current as of 2.6.33
+
+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:
+
+    <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:
+
+    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:
+
+    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):
+
+    /* 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:
+
+    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:
+
+    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:
+
+    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:
+
+    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:
+
+    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:
+
+    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:
+
+    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);
+    int videobuf_cgmbuf(struct videobuf_queue *q, struct video_mbuf *mbuf,
+                        int count);
+
+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.  videobuf_cgmbuf(), called from the driver's
+vidiocgmbuf() function, only exists if the V4L1 compatibility module has
+been selected with CONFIG_VIDEO_V4L1_COMPAT, so its use must be surrounded
+with #ifdef directives.
+
+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:
+
+    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:
+
+    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:
+
+    void *videobuf_to_vmalloc(struct videobuf_buffer *buf);
+
+For contiguous DMA drivers, the function to use is:
+
+    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.  Also worthwhile is the vivi driver
+(drivers/media/video/vivi.c), which is maintained as an example of how V4L2
+drivers should be written.  Vivi only uses the vmalloc() API, but it's good
+enough to get started with.  Note also that all of these calls are exported
+GPL-only, so they will not be available to non-GPL kernel modules.