On 11/21/2015 11:20 PM, Ran Shalit wrote:
> Hello,
>
> I am trying to understand the interrupt handler responsibility in
> v4l2, also with respect to dma usage. I see that it is not defined as
> part of the videobuf2 API.
>
> This is what I understand this far:
> 1. start_streaming is responsible for getting into "streaming" state.
> dma start should be trigggered at this point.
Right.
> 2. interrupt handler: is responsible for passing back the buffer to
> user using vb2_buffer_done() call.
Right.
>
> But what is the exact reponsibility of interrupt handler with respect
> to dma usage ?
Typically when the DMA has finished DMAing a frame it will generate an
interrupt.
The interrupt handler will then call vb2_buffer_done() handing the buffer back
to the vb2 framework. Think of it as who owns the buffer: when buf_queue is
called
the buffer is handed from vb2 to the driver, and the driver calls
vb2_buffer_done()
when it is finished with the buffer (i.e. the data is DMAed into the buffer) and
it hands it back to vb2.
> In some of the drivers I see that the interrupt start/stop dma, but in
> v4l2-pci-skeleton.c I don't see any usage of dma in the interrupt
> handler, so I'm not sure.
The interrupt handler is called in response of a DMA interrupt. How that
interrupt
is generated is hardware specific, so that's why you don't see it in the
skeleton
driver.
Regards,
Hans
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