Hello,
I'm working with an OMAP3530 based custom board. The board has 4
cameras attached to it, using the drivers/media/video/omap34xxcam.c and
.../ov3640.c and .../isp/isp*.c drivers. We've modified these drivers
slightly so we can mux an I2C bus to talk to each different camera.
When we want to use a specific camera, we tri-state all the other
cameras and enable the one we want. This works well, and we can get
images from all 4 cameras.
Now we'd like to take all 4 cameras and collage their images together to
produce a single stream showing all 4 images in each frame. I've
allocated a global frame buffer using kmalloc( ...,GFP_DMA). There's
just one of those, and we create it at the beginning of time and keep it
around forever. We also dma_map_single() it so we can DMA to it. The
idea being that, as each frame comes by, we want to use SDMA to copy it
at a reduced resolution into the correct quadrant of the global buffer,
then SDMA back from the global buffer into our frame.
So far in testing I think I have a good handle on the SDMA part. If I
kmalloc() a second buffer, I can SDMA back and forth, and I've got all
the SDMA settings correct to do what I want (verified by putting known
values in buffers and checking before vs after). Now I just need a
pointer suitable for SDMA I can use for the real frames when they come
by. In other words, I need to know the value to fill in an
omap_dma_channel_params.src_start for my first call to
omap_set_dma_params().
So how do I do this? I've hooked my new code in right before the call
to isp_buf->complete so I can do my thing there. So I have access to an
isp_buf and the videobuf_buffer contained therein.
The problem I'm running into (I think) is that omap34xxcam.c uses
videobuf-dma-sg to do its allocation and the videobuf_buffer I get is
using a scatterlist, and the pages in the scatterlist are
noncontiguous. In other words, if I use videobuf_to_dma(vb), the
videobuf_dmabuf I get back has a vmalloc of null and a bus_addr of null;
only the scatterlist and pages fields have valid values. There's no
contiguous memory pointer I can grab onto there.
How do I get a pointer suitable for SDMA? Will anything map this
scatterlist so it looks contiguous for SDMA?
I've tried changing omap34xxcam.c to use videobuf-dma-contig but that
didn't "just work" so I abandoned that line of investigation.
I've tried using dma_map_single on vb->map->start as well as
ispbuf->isp_addr, and several variations on that theme, without success.
I feel like I'm missing some fundamental piece of understanding, and I'm
hoping there's a magic call or two that will cure all my woes.
The only alternative I can come up with is to double my global buffer
size and take my nice two step process and break it into three phases,
(1) walk the scatterlist to SDMA from each page into the first half of
the global buffer, (2) SDMA from the first half of the global buffer
into the second half and finally (3) walk the scatterlist again, SDMAing
from the second half of the global buffer into each page in the
scatterlist. This seems ugly and messy and I feel there must be some
other way!
Any help is appreciated.
--Adam
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