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>
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>
