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Commit f0bb8dd9 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab
Browse files

[media] doc-rst: add pxa_camera documentation 



Convert pxa_camera to ReST format and add it to the
media/v4l-drivers book.

Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
parent 1bb6f32a

Documentation/media/v4l-drivers/index.rst

+1 −0
Original line number Diff line number Diff line
@@ -31,4 +31,5 @@ License". 
	omap3isp

	omap4_camera

	pvrusb2

	pxa_camera

	zr364xx

Documentation/media/v4l-drivers/pxa_camera.rst

+121 −103
Original line number Diff line number Diff line 
PXA-Camera Host Driver

======================



Author: Robert Jarzmik <robert.jarzmik@free.fr>



Constraints

-----------



a) Image size for YUV422P format

   All YUV422P images are enforced to have width x height % 16 = 0.

   This is due to DMA constraints, which transfers only planes of 8 byte
@@ -11,6 +14,7 @@ Constraints 


Global video workflow

---------------------



a) QCI stopped

   Initialy, the QCI interface is stopped.

   When a buffer is queued (pxa_videobuf_ops->buf_queue), the QCI starts.
@@ -28,6 +32,8 @@ Global video workflow 


c) Capture global finite state machine schema



.. code-block:: none



	+----+                             +---+  +----+

	| DQ |                             | Q |  | DQ |

	|    v                             |   v  |    v
@@ -78,6 +84,7 @@ Global video workflow 


DMA usage

---------



a) DMA flow

     - first buffer queued for capture

       Once a first buffer is queued for capture, the QCI is started, but data
@@ -95,12 +102,15 @@ DMA usage 


b) DMA prepared buffer will have this structure



.. code-block:: none



     +------------+-----+---------------+-----------------+

     | desc-sg[0] | ... | desc-sg[last] | finisher/linker |

     +------------+-----+---------------+-----------------+



This structure is pointed by dma->sg_cpu.

The descriptors are used as follows:



- desc-sg[i]: i-th descriptor, transferring the i-th sg

  element to the video buffer scatter gather

- finisher: has ddadr=DADDR_STOP, dcmd=ENDIRQEN
@@ -110,6 +120,8 @@ DMA usage 
"f" stands for finisher and "l" for linker.

A typical running chain is :



.. code-block:: none



         Videobuffer 1         Videobuffer 2

     +---------+----+---+  +----+----+----+---+

     | d0 | .. | dN | l |  | d0 | .. | dN | f |
@@ -119,6 +131,8 @@ DMA usage 


After the chaining is finished, the chain looks like :



.. code-block:: none



         Videobuffer 1         Videobuffer 2         Videobuffer 3

     +---------+----+---+  +----+----+----+---+  +----+----+----+---+

     | d0 | .. | dN | l |  | d0 | .. | dN | l |  | d0 | .. | dN | f |
@@ -136,6 +150,9 @@ DMA usage 
- DMA chain is Videobuffer1 + Videobuffer2

- pxa_videobuf_queue() is called to queue Videobuffer3

- DMA controller finishes Videobuffer2, and DMA stops



.. code-block:: none



      =>

         Videobuffer 1         Videobuffer 2

     +---------+----+---+  +----+----+----+---+
@@ -150,6 +167,8 @@ DMA usage 
- the DMA irq handler is called, which terminates Videobuffer2

- Videobuffer3 capture is not scheduled on DMA chain (as it stopped !!!)



.. code-block:: none



         Videobuffer 1         Videobuffer 2         Videobuffer 3

     +---------+----+---+  +----+----+----+---+  +----+----+----+---+

     | d0 | .. | dN | l |  | d0 | .. | dN | l |  | d0 | .. | dN | f |
@@ -165,10 +184,9 @@ DMA usage 
  and Videobuffer3 is scheduled on DMA chain.

- the DMA irq handler finishes



     Note: if DMA stops just after pxa_camera_check_link_miss() reads DDADR()

.. note::



     If DMA stops just after pxa_camera_check_link_miss() reads DDADR()

     value, we have the guarantee that the DMA irq handler will be called back

     when the DMA will finish the buffer, and pxa_camera_check_link_miss() will

     be called again, to reschedule Videobuffer3.
 


--

Author: Robert Jarzmik <robert.jarzmik@free.fr>