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cafe_ccic.rst

cafe_ccic.rst 2.5 KB
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  1. .. SPDX-License-Identifier: GPL-2.0
    2. 

  2. 

  3. The cafe_ccic driver
    4. 

  4. ====================
    5. 

  5. 

  6. Author: Jonathan Corbet <corbet@lwn.net>
    7. 

  7. 

  8. Introduction
    9. 

  9. ------------
    10. 

  10. 

  11. "cafe_ccic" is a driver for the Marvell 88ALP01 "cafe" CMOS camera
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  12. controller.  This is the controller found in first-generation OLPC systems,
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  13. and this driver was written with support from the OLPC project.
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  14. 

  15. Current status: the core driver works.  It can generate data in YUV422,
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  16. RGB565, and RGB444 formats.  (Anybody looking at the code will see RGB32 as
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  17. well, but that is a debugging aid which will be removed shortly).  VGA and
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  18. QVGA modes work; CIF is there but the colors remain funky.  Only the OV7670
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  19. sensor is known to work with this controller at this time.
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  20. 

  21. To try it out: either of these commands will work:
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  22. 

  23. .. code-block:: none
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  24. 

  25.      $ mplayer tv:// -tv driver=v4l2:width=640:height=480 -nosound
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  26.      $ mplayer tv:// -tv driver=v4l2:width=640:height=480:outfmt=bgr16 -nosound
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  27. 

  28. The "xawtv" utility also works; gqcam does not, for unknown reasons.
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  29. 

  30. Load time options
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  31. -----------------
    32. 

  32. 

  33. There are a few load-time options, most of which can be changed after
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  34. loading via sysfs as well:
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  35. 

  36.  - alloc_bufs_at_load:  Normally, the driver will not allocate any DMA
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  37.    buffers until the time comes to transfer data.  If this option is set,
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  38.    then worst-case-sized buffers will be allocated at module load time.
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  39.    This option nails down the memory for the life of the module, but
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  40.    perhaps decreases the chances of an allocation failure later on.
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  41. 

  42.  - dma_buf_size: The size of DMA buffers to allocate.  Note that this
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  43.    option is only consulted for load-time allocation; when buffers are
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  44.    allocated at run time, they will be sized appropriately for the current
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  45.    camera settings.
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  46. 

  47.  - n_dma_bufs: The controller can cycle through either two or three DMA
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  48.    buffers.  Normally, the driver tries to use three buffers; on faster
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  49.    systems, however, it will work well with only two.
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  50. 

  51.  - min_buffers: The minimum number of streaming I/O buffers that the driver
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  52.    will consent to work with.  Default is one, but, on slower systems,
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  53.    better behavior with mplayer can be achieved by setting to a higher
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  54.    value (like six).
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  55. 

  56.  - max_buffers: The maximum number of streaming I/O buffers; default is
    57. 

  57.    ten.  That number was carefully picked out of a hat and should not be
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  58.    assumed to actually mean much of anything.
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  59. 

  60.  - flip: If this boolean parameter is set, the sensor will be instructed to
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  61.    invert the video image.  Whether it makes sense is determined by how
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  62.    your particular camera is mounted.
    63.