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Commit f0bb8dd9 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab
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[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
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Documentation/media/v4l-drivers/index.rst
View file @ f0bb8dd9
......@@ -31,4 +31,5 @@ License".
omap3isp
omap4_camera
pvrusb2
pxa_camera
zr364xx
Documentation/media/v4l-drivers/pxa_camera.rst
View file @ f0bb8dd9
PXA-Camera Host Driver
======================
PXA-Camera Host Driver
======================
Author: Robert Jarzmik <robert.jarzmik@free.fr>
Constraints
-----------
a) Image size for YUV422P format
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
multiples.
......@@ -11,11 +14,12 @@ Constraints
Global video workflow
---------------------
a) QCI stopped
a) QCI stopped
Initialy, the QCI interface is stopped.
When a buffer is queued (pxa_videobuf_ops->buf_queue), the QCI starts.
b) QCI started
b) QCI started
More buffers can be queued while the QCI is started without halting the
capture. The new buffers are "appended" at the tail of the DMA chain, and
smoothly captured one frame after the other.
......@@ -26,7 +30,9 @@ Global video workflow
Once the last buffer is filled in, the QCI interface stops.
c) Capture global finite state machine schema
c) Capture global finite state machine schema
.. code-block:: none
+----+ +---+ +----+
| DQ | | Q | | DQ |
......@@ -34,27 +40,27 @@ Global video workflow
+-----------+ +------------------------+
| STOP | | Wait for capture start |
+-----------+ Q +------------------------+
+-> | QCI: stop | ------------------> | QCI: run | <------------+
| | DMA: stop | | DMA: stop | |
| +-----------+ +-----> +------------------------+ |
| / | |
| / +---+ +----+ | |
|capture list empty / | Q | | DQ | | QCI Irq EOF |
| / | v | v v |
| +--------------------+ +----------------------+ |
| | DMA hotlink missed | | Capture running | |
| +--------------------+ +----------------------+ |
| | QCI: run | +-----> | QCI: run | <-+ |
| | DMA: stop | / | DMA: run | | |
| +--------------------+ / +----------------------+ | Other |
| ^ /DMA still | | channels |
| | capture list / running | DMA Irq End | not |
| | not empty / | | finished |
| | / v | yet |
| +----------------------+ +----------------------+ | |
| | Videobuf released | | Channel completed | | |
| +----------------------+ +----------------------+ | |
+-- | QCI: run | | QCI: run | --+ |
+-> | QCI: stop | ------------------> | QCI: run | <------------+
| | DMA: stop | | DMA: stop | |
| +-----------+ +-----> +------------------------+ |
| / | |
| / +---+ +----+ | |
|capture list empty / | Q | | DQ | | QCI Irq EOF |
| / | v | v v |
| +--------------------+ +----------------------+ |
| | DMA hotlink missed | | Capture running | |
| +--------------------+ +----------------------+ |
| | QCI: run | +-----> | QCI: run | <-+ |
| | DMA: stop | / | DMA: run | | |
| +--------------------+ / +----------------------+ | Other |
| ^ /DMA still | | channels |
| | capture list / running | DMA Irq End | not |
| | not empty / | | finished |
| | / v | yet |
| +----------------------+ +----------------------+ | |
| | Videobuf released | | Channel completed | | |
| +----------------------+ +----------------------+ | |
+-- | QCI: run | | QCI: run | --+ |
| DMA: run | | DMA: run | |
+----------------------+ +----------------------+ |
^ / | |
......@@ -78,7 +84,8 @@ Global video workflow
DMA usage
---------
a) DMA flow
a) DMA flow
- first buffer queued for capture
Once a first buffer is queued for capture, the QCI is started, but data
transfer is not started. On "End Of Frame" interrupt, the irq handler
......@@ -93,22 +100,27 @@ DMA usage
- finishing the last videobuffer
On the DMA irq of the last videobuffer, the QCI is stopped.
b) DMA prepared buffer will have this structure
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
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
- linker: has ddadr= desc-sg[0] of next video buffer, dcmd=0
- finisher: has ddadr=DADDR_STOP, dcmd=ENDIRQEN
- linker: has ddadr= desc-sg[0] of next video buffer, dcmd=0
For the next schema, let's assume d0=desc-sg[0] .. dN=desc-sg[N],
"f" stands for finisher and "l" for linker.
A typical running chain is :
For the next schema, let's assume d0=desc-sg[0] .. dN=desc-sg[N],
"f" stands for finisher and "l" for linker.
A typical running chain is :
.. code-block:: none
Videobuffer 1 Videobuffer 2
+---------+----+---+ +----+----+----+---+
......@@ -117,7 +129,9 @@ DMA usage
| |
+----+
After the chaining is finished, the chain looks like :
After the chaining is finished, the chain looks like :
.. code-block:: none
Videobuffer 1 Videobuffer 2 Videobuffer 3
+---------+----+---+ +----+----+----+---+ +----+----+----+---+
......@@ -127,15 +141,18 @@ DMA usage
+----+ +----+
new_link
c) DMA hot chaining timeslice issue
c) DMA hot chaining timeslice issue
As DMA chaining is done while DMA _is_ running, the linking may be done
while the DMA jumps from one Videobuffer to another. On the schema, that
would be a problem if the following sequence is encountered :
- DMA chain is Videobuffer1 + Videobuffer2
- pxa_videobuf_queue() is called to queue Videobuffer3
- DMA controller finishes Videobuffer2, and DMA stops
As DMA chaining is done while DMA _is_ running, the linking may be done
while the DMA jumps from one Videobuffer to another. On the schema, that
would be a problem if the following sequence is encountered :
.. code-block:: none
- DMA chain is Videobuffer1 + Videobuffer2
- pxa_videobuf_queue() is called to queue Videobuffer3
- DMA controller finishes Videobuffer2, and DMA stops
=>
Videobuffer 1 Videobuffer 2
+---------+----+---+ +----+----+----+---+
......@@ -144,11 +161,13 @@ DMA usage
| | |
+----+ +-- DMA DDADR loads DDADR_STOP
- pxa_dma_add_tail_buf() is called, the Videobuffer2 "finisher" is
- pxa_dma_add_tail_buf() is called, the Videobuffer2 "finisher" is
replaced by a "linker" to Videobuffer3 (creation of new_link)
- pxa_videobuf_queue() finishes
- the DMA irq handler is called, which terminates Videobuffer2
- Videobuffer3 capture is not scheduled on DMA chain (as it stopped !!!)
- pxa_videobuf_queue() finishes
- 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
+---------+----+---+ +----+----+----+---+ +----+----+----+---+
......@@ -159,16 +178,15 @@ DMA usage
new_link
DMA DDADR still is DDADR_STOP
- pxa_camera_check_link_miss() is called
- pxa_camera_check_link_miss() is called
This checks if the DMA is finished and a buffer is still on the
pcdev->capture list. If that's the case, the capture will be restarted,
and Videobuffer3 is scheduled on DMA chain.
- the DMA irq handler finishes
- the DMA irq handler finishes
.. note::
Note: if DMA stops just after pxa_camera_check_link_miss() reads DDADR()
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>
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