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authorJonathan Corbet <corbet-v4l@lwn.net>2006-11-04 09:25:53 -0300
committerMauro Carvalho Chehab <mchehab@infradead.org>2006-12-10 08:51:13 -0200
commitd905b382d797a213e15868cbf3204f50ed52e30b (patch)
tree9e328aa8e273bcc0656cd0bb4a51020ea10ef008 /Documentation
parent9c4dfadbde3cfa78b92c28597125b8c41d36ffd0 (diff)
V4L/DVB (4797): Marvell 88ALP01 "cafe" driver
A driver for the Marvell M88ALP01 "CAFE" CMOS integrated camera controller. This driver has been renamed "cafe_ccic" since my previous patch set. Signed-off-by: Jonathan Corbet <corbet@lwn.net> Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
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+"cafe_ccic" is a driver for the Marvell 88ALP01 "cafe" CMOS camera
+controller. This is the controller found in first-generation OLPC systems,
+and this driver was written with support from the OLPC project.
+
+Current status: the core driver works. It can generate data in YUV422,
+RGB565, and RGB444 formats. (Anybody looking at the code will see RGB32 as
+well, but that is a debugging aid which will be removed shortly). VGA and
+QVGA modes work; CIF is there but the colors remain funky. Only the OV7670
+sensor is known to work with this controller at this time.
+
+To try it out: either of these commands will work:
+
+ mplayer tv:// -tv driver=v4l2:width=640:height=480 -nosound
+ mplayer tv:// -tv driver=v4l2:width=640:height=480:outfmt=bgr16 -nosound
+
+The "xawtv" utility also works; gqcam does not, for unknown reasons.
+
+There are a few load-time options, most of which can be changed after
+loading via sysfs as well:
+
+ - alloc_bufs_at_load: Normally, the driver will not allocate any DMA
+ buffers until the time comes to transfer data. If this option is set,
+ then worst-case-sized buffers will be allocated at module load time.
+ This option nails down the memory for the life of the module, but
+ perhaps decreases the chances of an allocation failure later on.
+
+ - dma_buf_size: The size of DMA buffers to allocate. Note that this
+ option is only consulted for load-time allocation; when buffers are
+ allocated at run time, they will be sized appropriately for the current
+ camera settings.
+
+ - n_dma_bufs: The controller can cycle through either two or three DMA
+ buffers. Normally, the driver tries to use three buffers; on faster
+ systems, however, it will work well with only two.
+
+ - min_buffers: The minimum number of streaming I/O buffers that the driver
+ will consent to work with. Default is one, but, on slower systems,
+ better behavior with mplayer can be achieved by setting to a higher
+ value (like six).
+
+ - max_buffers: The maximum number of streaming I/O buffers; default is
+ ten. That number was carefully picked out of a hat and should not be
+ assumed to actually mean much of anything.
+
+ - flip: If this boolean parameter is set, the sensor will be instructed to
+ invert the video image. Whether it makes sense is determined by how
+ your particular camera is mounted.
+
+Work is ongoing with this driver, stay tuned.
+
+jon
+
+Jonathan Corbet
+corbet@lwn.net