63 lines
2.5 KiB
ReStructuredText
63 lines
2.5 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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The cafe_ccic driver
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====================
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Author: Jonathan Corbet <corbet@lwn.net>
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Introduction
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------------
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"cafe_ccic" is a driver for the Marvell 88ALP01 "cafe" CMOS camera
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controller. This is the controller found in first-generation OLPC systems,
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and this driver was written with support from the OLPC project.
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Current status: the core driver works. It can generate data in YUV422,
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RGB565, and RGB444 formats. (Anybody looking at the code will see RGB32 as
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well, but that is a debugging aid which will be removed shortly). VGA and
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QVGA modes work; CIF is there but the colors remain funky. Only the OV7670
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sensor is known to work with this controller at this time.
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To try it out: either of these commands will work:
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.. code-block:: none
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$ mplayer tv:// -tv driver=v4l2:width=640:height=480 -nosound
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$ mplayer tv:// -tv driver=v4l2:width=640:height=480:outfmt=bgr16 -nosound
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The "xawtv" utility also works; gqcam does not, for unknown reasons.
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Load time options
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-----------------
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There are a few load-time options, most of which can be changed after
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loading via sysfs as well:
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- alloc_bufs_at_load: Normally, the driver will not allocate any DMA
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buffers until the time comes to transfer data. If this option is set,
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then worst-case-sized buffers will be allocated at module load time.
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This option nails down the memory for the life of the module, but
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perhaps decreases the chances of an allocation failure later on.
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- dma_buf_size: The size of DMA buffers to allocate. Note that this
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option is only consulted for load-time allocation; when buffers are
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allocated at run time, they will be sized appropriately for the current
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camera settings.
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- n_dma_bufs: The controller can cycle through either two or three DMA
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buffers. Normally, the driver tries to use three buffers; on faster
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systems, however, it will work well with only two.
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- min_buffers: The minimum number of streaming I/O buffers that the driver
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will consent to work with. Default is one, but, on slower systems,
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better behavior with mplayer can be achieved by setting to a higher
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value (like six).
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- max_buffers: The maximum number of streaming I/O buffers; default is
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ten. That number was carefully picked out of a hat and should not be
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assumed to actually mean much of anything.
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- flip: If this boolean parameter is set, the sensor will be instructed to
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invert the video image. Whether it makes sense is determined by how
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your particular camera is mounted.
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