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2 commits

Author SHA1 Message Date
Robert Jarzmik
5660009364 V4L/DVB (11613): pxa_camera: Documentation of the FSM
After DMA redesign, the pxa_camera dynamic behaviour should
be documented so that future contributors understand how it
works, and improve it.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
2009-06-16 18:20:44 -03:00
Robert Jarzmik
256b02332a V4L/DVB (11321): pxa_camera: Redesign DMA handling
The DMA transfers in pxa_camera showed some weaknesses in
multiple queued buffers context :
 - poll/select problem
   The bug shows up with capture_example tool from v4l2 hg
   tree. The process just "stalls" on a "select timeout".

 - multiple buffers DMA starting
   When multiple buffers were queued, the DMA channels were
   always started right away. This is not optimal, as a
   special case appears when the first EOF was not yet
   reached, and the DMA channels were prematurely started.

 - Maintainability
   DMA code was a bit obfuscated. Rationalize the code to be
   easily maintainable by anyone.

 - DMA hot chaining
   DMA is not stopped anymore to queue a buffer, the buffer
   is queued with DMA running. As a tribute, a corner case
   exists where chaining happens while DMA finishes the
   chain, and the capture is restarted to deal with the
   missed link buffer.

This patch attemps to address these issues / improvements.

 create mode 100644 Documentation/video4linux/pxa_camera.txt

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
2009-04-06 21:43:45 -03:00