diff options
| -rw-r--r-- | Documentation/media/v4l-drivers/index.rst | 1 | ||||
| -rw-r--r-- | Documentation/media/v4l-drivers/pxa_camera.rst | 224 |
2 files changed, 122 insertions, 103 deletions
diff --git a/Documentation/media/v4l-drivers/index.rst b/Documentation/media/v4l-drivers/index.rst index e88ce12074ae..eb0ed669545e 100644 --- a/Documentation/media/v4l-drivers/index.rst +++ b/Documentation/media/v4l-drivers/index.rst @@ -31,4 +31,5 @@ License". omap3isp omap4_camera pvrusb2 + pxa_camera zr364xx diff --git a/Documentation/media/v4l-drivers/pxa_camera.rst b/Documentation/media/v4l-drivers/pxa_camera.rst index 51ed1578b0e8..554f91b04e70 100644 --- a/Documentation/media/v4l-drivers/pxa_camera.rst +++ b/Documentation/media/v4l-drivers/pxa_camera.rst @@ -1,84 +1,91 @@ - PXA-Camera Host Driver - ====================== +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 - multiples. + +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. 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. - - 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. - - Once a buffer is filled in the QCI interface, it is marked as "DONE" and - removed from the active buffers list. It can be then requeud or dequeued by - userland application. - - Once the last buffer is filled in, the QCI interface stops. - - c) Capture global finite state machine schema - - +----+ +---+ +----+ - | DQ | | Q | | DQ | - | v | v | v - +-----------+ +------------------------+ - | 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 | --+ | - | DMA: run | | DMA: run | | - +----------------------+ +----------------------+ | - ^ / | | - | no overrun / | overrun | - | / v | - +--------------------+ / +----------------------+ | - | Frame completed | / | Frame overran | | - +--------------------+ <-----+ +----------------------+ restart frame | - | QCI: run | | QCI: stop | --------------+ - | DMA: run | | DMA: stop | - +--------------------+ +----------------------+ - - Legend: - each box is a FSM state - - each arrow is the condition to transition to another state - - an arrow with a comment is a mandatory transition (no condition) - - arrow "Q" means : a buffer was enqueued - - arrow "DQ" means : a buffer was dequeued - - "QCI: stop" means the QCI interface is not enabled - - "DMA: stop" means all 3 DMA channels are stopped - - "DMA: run" means at least 1 DMA channel is still running + +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 + 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. + + Once a buffer is filled in the QCI interface, it is marked as "DONE" and + removed from the active buffers list. It can be then requeud or dequeued by + userland application. + + Once the last buffer is filled in, the QCI interface stops. + +c) Capture global finite state machine schema + +.. code-block:: none + + +----+ +---+ +----+ + | DQ | | Q | | DQ | + | v | v | v + +-----------+ +------------------------+ + | 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 | --+ | + | DMA: run | | DMA: run | | + +----------------------+ +----------------------+ | + ^ / | | + | no overrun / | overrun | + | / v | + +--------------------+ / +----------------------+ | + | Frame completed | / | Frame overran | | + +--------------------+ <-----+ +----------------------+ restart frame | + | QCI: run | | QCI: stop | --------------+ + | DMA: run | | DMA: stop | + +--------------------+ +----------------------+ + + Legend: - each box is a FSM state + - each arrow is the condition to transition to another state + - an arrow with a comment is a mandatory transition (no condition) + - arrow "Q" means : a buffer was enqueued + - arrow "DQ" means : a buffer was dequeued + - "QCI: stop" means the QCI interface is not enabled + - "DMA: stop" means all 3 DMA channels are stopped + - "DMA: run" means at least 1 DMA channel is still running 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 - 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 +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 + +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 : - 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 + +.. 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 - 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_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 !!!) + +.. 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 - 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 +- 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 - 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> |