Re: [PATCH 2/4] pxa_camera: Redesign DMA handling

[Robert Jarzmik <robert.jarzmik@free.fr>]

Robert Jarzmik <robert.jarzmik@free.fr> writes:

> Guennadi Liakhovetski <g.liakhovetski@gmx.de> writes:
>
>>> +	for (i = 0; i < pcdev->channels; i++) {
>>> +		pcdev->sg_tail[i] = buf->dmas[i].sg_cpu + buf->dmas[i].sglen;
>>> +		pcdev->sg_tail[i]->ddadr = DDADR_STOP;
>
>> This function is now called "live" with running DMA, and you first append 
>> the chain, and only then terminate it... It should be ok because it is 
>> done with switched off IRQs, and DMA must be still at tail - 1 to 
>> automatically continue onto the appended chain, so, you should have enough 
>> time in 100% of cases, still it would look better to first terminate the 
>> chain and then append it.

> Correct. I'll invert the 2 assignments.

At second thought, I think I'll change this. The first assignment doesn't append
the chain, it just moves where sg_tail points at. The "chain append" was
previously done in "pxa_dma_add_tail_buf".

So the correct thing to do is to displace the "DDADR_STOP" assignment into
"pxa_dma_add_tail_buf", to make the "STOP" on the last descriptor of the newest
tail buffer. This "STOP" should be set up _before_ the buffer is queued.

I'll amend that.

Cheers.

--
Robert